EVALUATION OF EROSION AND SEDIMENT CONTROL BEST MANAGEMENT 
 
 PRACTICES: USE OF SILT FENCE TIEBACK SYSTEMS AND ANIONIC 
 
POLYACRYLAMIDE ON HIGHWAY CONSTRUCTION SITES 
 
 
 
 
Except where reference is made to the work of others, the work described in this thesis is 
my own or was done in collaboration with my advisory committee.  This thesis does not 
include propriety or classified information. 
 
 
 
 
 
 
 
___________________________________ 
Justin Scott McDonald 
 
 
 
 
 
Certificate of Approval: 
 
 
______________________________  ______________________________ 
T. Prabhakar Clement, Co-Chair   Wesley C. Zech, Co-Chair  
Associate Professor     Assistant Professor 
Civil Engineering     Civil Engineering 
 
 
 
______________________________  ______________________________ 
Puneet Srivastava     Joe F. Pittman 
Assistant Professor     Interim Dean 
Biosystems Engineering    Graduate School
 
  
EVALUATION OF EROSION AND SEDIMENT CONTROL BEST MANAGEMENT 
 
 PRACTICES: USE OF SILT FENCE TIEBACK SYSTEMS AND ANIONIC 
 
POLYACRYLAMIDE ON HIGHWAY CONSTRUCTION SITES 
 
 
 
 
 
Justin Scott McDonald 
 
 
 
 
 
 
 
A Thesis 
 
Submitted to 
 
the Graduate Faculty of 
 
Auburn University 
 
in Partial Fulfillment of the 
 
Requirements for the 
 
Degree of 
 
Master of Science 
 
 
 
 
 
Auburn, Alabama 
August 4, 2007
 iii
EVALUATION OF EROSION AND SEDIMENT CONTROL BEST MANAGEMENT 
 
 PRACTICES: USE OF SILT FENCE TIEBACK SYSTEMS AND ANIONIC 
 
POLYACRYLAMIDE ON HIGHWAY CONSTRUCTION SITES 
 
 
 
 
Justin Scott McDonald 
 
 
 
 
Permission is granted to Auburn University to make copies of this thesis at its discretion, 
upon request of individuals or institutions and at their expense.  The author reserves all 
publication rights. 
 
 
 
 
______________________________ 
       Signature of Author 
 
 
       ______________________________ 
       Date of Graduation 
 iv
VITA 
 
Justin Scott McDonald, son of Ronald J. McDonald and Debra B. Bradshaw, was 
born on October 25, 1982, in Mobile, AL.  He graduated high school from Mobile 
Christian School in Mobile, AL in 2000.  After graduating, he attended Auburn 
University in Auburn, AL and graduated with a Bachelor of Civil Engineering degree in 
December of 2005.  In January 2006, he entered the Graduate School at Auburn 
University to pursue a Master of Science in Civil Engineering.  He was married to 
Kimberly R. Price on June 3, 2006.   
 v
THESIS ABSTRACT 
EVALUATION OF EROSION AND SEDIMENT CONTROL BEST MANAGEMENT 
 
 PRACTICES: USE OF SILT FENCE TIEBACK SYSTEMS AND ANIONIC 
 
POLYACRYLAMIDE ON HIGHWAY CONSTRUCTION SITES 
 
Justin Scott McDonald 
 
Master of Science in Civil Engineering, August 4, 2007 
(B.C.E, Auburn University, 2005) 
 
 
141 Typed Pages 
 
Directed by Wesley C. Zech and T. Prabhakar Clement 
 
 Every year the construction process exposes millions of acres of earth to the 
elements of wind, rain, and snow.  This greatly increases the potential for erosion; 
therefore, the need for efficient erosion and sediment control practices is a high priority.  
In this research, silt fence tieback (a.k.a. ?j-hook?) systems and anionic polyacrylamide 
(PAM) were investigated to determine their effectiveness as erosion and sediment control 
technologies.  In the first phase of this research effort, a computational design procedure 
used to determine the storage capacity of silt fence tieback systems was outlined and a 
Visual Basic (VBA) coded spreadsheet design tool was developed to assist practitioners 
in the proper design of silt fence tieback systems.  This tool was then used to design a silt 
fence tieback system on an Alabama Department of Transportation (ALDOT) job site and 
 vi
the performance was monitored over multiple rainfall events.  The results from this phase 
of the study show that the silt fence tiebacks were very effective at containing transported 
sediment from their contributing drainage areas and preventing erosion from occurring 
along the toe of the fence.   
In the second phase of the research effort, intermediate-scale experiments were 
performed to determine the effectiveness of dry granular anionic polyacrylamide (PAM) 
as an erosion control BMP.  Three experimental scenarios were evaluated which included 
a bare untreated soil (control experiment) and PAM treated soil at application rates of 20 
and 40 lb/ac.  We also investigated whether PAM, when used as an erosion control BMP, 
provided sediment control benefits by decreasing the settling time of suspended solids in 
the surface runoff.  The results from this phase of the research show that PAM applied at 
40 lb/ac effectively reduced erosion and the settling time of suspended solids in the 
surface runoff.  PAM applied at 20 lb/ac, on the other hand, provided little erosion 
control benefits but did reduce the settling time of suspended solids in most instances.   
 
 
 
 
 
 
 vii
ACKNOWLEDGEMENTS 
 
 The author would like to extend a special thanks to Dr. Wesley C. Zech and Dr. T 
Prabhakar Clement for their time and guidance throughout this research effort.  The 
author would also like to thank the Alabama Department of Transportation (ALDOT) for 
funding the project, the Auburn University Civil Engineering Department for their 
financial support, Mr. Steven Iwinski of Applied Polymer Systems, Inc. for supplying the 
polymers used in the research, and Mr. Joel Horton, Mr. David Graham, Mr. Elliot Smith, 
and Mr. John Gunter for their help in preparing and performing multiple experiments 
during this research.  Finally, the author would like to especially thank his wife, 
Kimberly P. McDonald, for her love and support throughout the entire graduate school 
process.   
 viii
Style manual or journal used Auburn University Graduate School Guide to Preparation of 
Master?s Thesis   
 
Computer software used Microsoft Word 2003, Microsoft Excel 2003, Microsoft 
PowerPoint 2003 and MicroStation v8
 ix
TABLE OF CONTENTS 
 
LIST OF TABLES ??????????????????????????..... xi 
 
LIST OF FIGURES ??????????????????????????.. xii 
 
 
CHAPTER ONE 
INTRODUCTION  
1.1 BACKGROUND ................................................................................................ 1 
1.2 THE EROSION PROCESS ................................................................................ 2 
1.3 BEST MANAGEMENT PRACTICES (BMPs)................................................. 3 
1.4 RESEARCH OBJECTIVES ............................................................................... 5 
1.5 ORGANIZATION OF THESIS ......................................................................... 6
 
CHAPTER TWO 
DESIGN OF SILT FENCE TIEBACK SYSTEMS  
2.1 INTRODUCTION .............................................................................................. 8 
2.2 STORAGE CAPACITIES OF SILT FENCE TIEBACK SYSTEMS ............. 10 
2.2.1 Maximum Storage Capacity Calculation Procedure................................. 12 
2.2.2 Storage Capacities for More Frequent Tieback Configurations ............... 18 
2.2.3 Sensitivity Analysis .................................................................................. 22 
2.3 SILT FENCE TIEBACK CONFIGURATION DESIGN TOOL..................... 25 
2.3.1 Stormwater Runoff Volume Component.................................................. 26 
2.3.2 Silt Fence Storage Capacity Computation ................................................ 28 
2.3.3 Case Study: Application of the Silt Fence Tieback Design Tool ............. 30 
2.4 CONCLUSION................................................................................................. 45
 
CHAPTER THREE 
LITERATURE REVIEW: USE OF PAM AS AN EROSION AND SEDIMENT 
CONTROL BMP  
3.1 INTRODUCTION ............................................................................................ 46 
3.2 POLYMERS USED FOR EROSION AND SEDIMENT CONTROL............ 47 
3.2.1 Variables to Consider when Selecting a Polymer..................................... 47 
3.2.2 Applying Polymers ................................................................................... 50 
3.2.3 Previous Research on the Effectiveness of Polymers............................... 51 
3.3 SUMMARY...................................................................................................... 60
 x
CHAPTER FOUR 
INTERMEDIATE-SCALE EROSION CONTROL EXPERIMENTS USING PAM 
4.1 INTRODUCTION ............................................................................................ 62 
4.2 INTERMEDIATE-SCALE MODEL................................................................ 62 
4.2.1 Soil Plot Design ........................................................................................ 65 
4.2.2 Rainfall Simulator Design......................................................................... 68 
4.3 EXPERIMENTAL DESIGN ............................................................................ 69 
4.3.1 Polymer Selection ..................................................................................... 69 
4.3.2 Soil Plot Preparation ................................................................................. 70 
4.3.3 Rainfall Regimen Used for Testing .......................................................... 71 
4.3.4 Data Collection Procedure ........................................................................ 72 
4.4 RESULTS AND DISCUSSION....................................................................... 73 
4.4.1 Cumulative Volume versus Time ............................................................. 74 
4.4.2 Cumulative Surface Runoff Volume versus Time.................................... 77 
4.4.3 Cumulative Soil Loss versus Time ........................................................... 80 
4.4.4 Turbidity Results....................................................................................... 87 
4.5 CONCLUSION................................................................................................. 97 
 
CHAPTER FIVE 
CONCLUSIONS AND RECOMMENDATIONS 
5.1 INTRODUCTION .......................................................................................... 100 
5.2 SILT FENCE TIEBACK SYSTEMS ............................................................. 101 
5.3 INTERMEDIATE-SCALE EROSION CONTROL EXPERIMENTS USING 
PAM................................................................................................................ 103 
5.4 RECOMMENDED FURTHER RESEARCH ................................................ 105 
5.4.1 Silt Fence Tieback Systems .................................................................... 105 
5.4.2 PAM as an Erosion Control Technology................................................ 105 
 
REFERENCES ???????????????????????????... 107 
APPENDICES ???????????????????????????? 110 
 APPENDIX A ????????????????????????? 111 
 APPENDIX B ????????????????????????? 114 
 APPENDIX C ????????????????????????? 117 
 APPENDIX D ????????????????????????? 119 
 APPENDIX E ?????????????????????????  121 
 APPENDIX F ????????????????????????? 124
 xi
LIST OF TABLES 
 
Table 2.1  Test Site Characteristics................................................................................... 31 
Table 2.2  Rainfall at Test Site.......................................................................................... 36 
Table 4.1  Water Balance: Left Section............................................................................ 76 
Table 4.2  Water Balance: Center Section........................................................................ 76 
Table 4.3  Water Balance: Right Section.......................................................................... 77 
Table 4.4  Surface Runoff Statistics: Three Soil Plots Combined.................................... 80 
Table 4.5  Soil Loss Reduction for PAM Applied at 20 lb/ac. ......................................... 86 
Table 4.6  Soil Loss Reduction for PAM Applied at 40 lb/ac. ......................................... 86 
Table 4.7  Initial Turbidity................................................................................................ 97 
Table 4.8  Turbidity After 15 Minutes of Settling Time................................................... 97 
 xii
LIST OF FIGURES 
 
Figure 2.1  Silt Fence Tieback System ............................................................................... 9 
Figure 2.2  Typical Silt Fence Tieback Section................................................................ 11 
Figure 2.3  Total Storage Volume..................................................................................... 13 
Figure 2.4  Volume Stored on Fill Slope (V
1
). ................................................................. 13 
Figure 2.5  Projection of V
1
 in the x-y Plane.................................................................... 15 
Figure 2.6  Maximum Storage Volume on Existing Ground (V
2
).................................... 16 
Figure 2.7  Storage Volume for Scenario 1. ..................................................................... 19 
Figure 2.8  Storage Volume for Scenario 2. ..................................................................... 19 
Figure 2.9  Modified Storage Volume on Existing Ground (V
2modified
)............................ 20 
Figure 2.10  Projection of Maximum and Modified Storage Volumes on Existing Ground 
(V
2
).............................................................................................................. 20 
Figure 2.11  Constant S
1
, S
2 
and S
3
; Varying L
1
............................................................... 23 
Figure 2.12  Constant L
1, 
S
2 
and S
3
; Varying S
1
. .............................................................. 24 
Figure 2.13  Constant L
1, 
S
1 
and S
3
; Varying S
2
. .............................................................. 24 
Figure 2.14  Constant L
1, 
S
1 
and S
2
; Varying S
3
. .............................................................. 25 
Figure 2.15  Silt Fence Storage Capacity for Various Tieback Configurations. .............. 29 
Figure 2.16  Experimental Test Site. ................................................................................ 31 
Figure 2.17  Cross-Section of Field Test Site Roadway................................................... 32
 xiii
Figure 2.18  Silt Fence Design Tool Used for Test Site. .................................................. 33 
Figure 2.19  Six Tieback Sections After First Three Rainfall Events. ............................. 37 
Figure 2.20  Sedimentation Profile Along the Fence of the Tieback System................... 38 
Figure 2.21  Six Tieback Sections After the Fourth Rainfall Event. ................................ 40 
Figure 2.22  Upslope End of Linear Silt Fence w/ Little Sedimentation.......................... 41 
Figure 2.23  Downslope End of Linear............................................................................. 41 
Figure 2.24  Exposed Toe of Fence #1. ............................................................................ 42 
Figure 2.25  Exposed Toe of Fence #2. ............................................................................ 42 
Figure 2.26  Sedimentation Profile Along the Fence of the Linear System. .................... 42 
Figure 2.27  Before Scour Hole at Downslope End of Linear Fence. .............................. 43 
Figure 2.28  Scour Hole at Downslope End of Linear Fence. .......................................... 43 
Figure 2.29  Upslope End of Linear Fence w/ Little Sedimentation After Fourth Storm. 44 
Figure 2.30  Downslope End of Linear Fence w/ Heavy Sedimentation After Fourth 
Storm. .......................................................................................................... 44 
Figure 2.31  Exposed Toe of Fence After Fourth Storm. ................................................. 44 
Figure 2.32  Exposed Toe of Fence After Fourth Storm. ................................................. 44 
Figure 3.1  Polymer Structures ......................................................................................... 49 
Figure 4.1  Intermediate-Scale Model Designed by Halverson (2006). ........................... 63 
Figure 4.2  Modified Intermediate-Scale Erosion Model. ................................................ 64 
Figure 4.3  Intermediate-Scale Model After Installation of EPS Material. ...................... 66 
Figure 4.4  Intermediate-Scale Model After Installation of Geotextile Filter Fabric. ...... 66 
Figure 4.5  Intermediate-Scale Model After Installation of Silty Sand Material.............. 67 
Figure 4.6  Cross-Section of Soil Plots............................................................................. 67 
 xiv
Figure 4.7  Rainfall Simulator Configuration................................................................... 68 
Figure 4.8  1/8HH-3.6SQ Fulljet Spray      Nozzle........................................................... 69 
Figure 4.9  F-405 Series In-Line Flow Meter................................................................... 69 
Figure 4.10  705 Silt Stop Powder.................................................................................... 70 
Figure 4.11  Collection Buckets for Surface Runoff. ....................................................... 72 
Figure 4.12  Hayward Single-Length 1 Micron Filter Bags. ............................................ 72 
Figure 4.13  Cumulative Volume vs. Time: Left Soil Plot............................................... 74 
Figure 4.14  Cumulative Volume vs. Time: Center Soil Plot........................................... 75 
Figure 4.15  Cumulative Volume vs. Time: Right Soil Plot............................................. 75 
Figure 4.16  Cumulative Surface Runoff Volume vs. Time: Left Soil Plot. .................... 78 
Figure 4.17  Cumulative Surface Runoff Volume vs. Time: Center Soil Plot. ................ 78 
Figure 4.18  Cumulative Surface Runoff Volume vs. Time: Right Soil Plot. .................. 79 
Figure 4.19  Cumulative Soil Loss vs. Time: Left Soil Plot............................................. 81 
Figure 4.20  Cumulative Soil Loss vs. Time: Center Soil Plot......................................... 81 
Figure 4.21  Cumulative Soil Loss vs. Time: Right Soil Plot........................................... 82 
Figure 4.22  Average Cumulative Soil Loss vs. Time for all Three Soil Plots ................ 82 
Figure 4.23  Soil Plots After Run 1................................................................................... 84 
Figure 4.24  Soil Plots After Run 2................................................................................... 85 
Figure 4.25  Soil Plots After Run 3................................................................................... 86 
Figure 4.26  Turbidity of Surface Runoff vs. Time: Left Soil Plot. ................................. 87 
Figure 4.27  Turbidity of Surface Runoff vs. Time: Center Soil Plot. ............................. 88 
Figure 4.28  Turbidity of Surface Runoff vs. Time: Right Soil Plot. ............................... 88 
Figure 4.29  Turbidity vs. Settling Time for Run 1 (1 min). ............................................ 90 
 xv
Figure 4.30  Turbidity vs. Settling Time for Run 1 (5 min). ............................................ 90 
Figure 4.31  Turbidity vs. Settling Time for Run 1 (10 min). .......................................... 91 
Figure 4.32  Turbidity vs. Settling Time for Run 1 (15 min). .......................................... 91 
Figure 4.33  Turbidity vs. Settling Time for Run 2 (1 min). ............................................ 92 
Figure 4.34  Turbidity vs. Settling Time for Run 2 (5 min). ............................................ 92 
Figure 4.35  Turbidity vs. Settling Time for Run 2 (10 min). .......................................... 93 
Figure 4.36  Turbidity vs. Settling Time for Run 2 (15 min). .......................................... 93 
Figure 4.37  Turbidity vs. Settling Time for Run 3 (1 min). ............................................ 94 
Figure 4.38  Turbidity vs. Settling Time for Run 3 (5 min). ............................................ 94 
Figure 4.39  Turbidity vs. Settling Time for Run 3 (10 min). .......................................... 95 
Figure 4.40  Turbidity vs. Settling Time for Run 3 (15 min). .......................................... 95 
 1
CHAPTER ONE 
INTRODUCTION 
1  
1.1 BACKGROUND 
Nonpoint source pollution is a very important environmental issue facing our 
society today.  Nonpoint source pollution can be defined as pollution that comes from a 
diffuse source and is driven by rainfall or snowmelt moving over or through the land.  
Some sources of nonpoint source pollution include sediment from improperly managed 
construction sites, oil, grease, and toxic chemicals from urban runoff, bacteria and 
nutrients from livestock, and faulty septic systems.  In many U.S. states, nonpoint source 
pollution is the leading cause of water quality problems which affect drinking water, 
recreation, fisheries, and wildlife (U.S. EPA, 1994).   
 One of the most widely recognized causes of nonpoint source pollution is the 
sediment load discharged from poorly managed construction sites.  The construction 
process exposes bare earth to the elements of wind, rain, and snow which greatly increase 
the potential for erosion.  If proper nonpoint source pollution abatement methods are not 
followed, eroded material from construction sites can end up in streams and other water 
bodies.  It is estimated that in the U.S. alone, over 80 million tons of sediment are washed 
from construction sites into surface water bodies each year (Novotny, 2003).  This 
 2
process can be devastating to the chemical, physical, and biological integrity of streams, 
rivers, lakes, and estuaries.  Some of the environmental effects of erosion and 
sedimentation include loss of storage capacity of reservoirs, deterioration of fish 
spawning areas and habitat for other stream organisms, and increased nutrient loadings 
within streams (Novotny, 2003).  With increasing growth and development throughout 
the world, the need to develop better methods for preventing erosion and controlling 
sediment on construction sites is a high priority.   
1.2 THE EROSION PROCESS 
In order to establish a good understanding of the role that erosion plays in nonpoint 
source pollution, the basics of the erosion process will be outlined in this section.  The 
erosion process can be defined as the wearing down the earth?s surface by the elements of 
wind, rain, and snow where sediment is detached, transported, and deposited downslope.  
This is a natural process but is often increased due to the high rate of construction 
occurring around the world.  Factors influencing erosion include climate, topography, soil 
type, and vegetative cover (Alabama Soil and Water Conservation Committee, 2003a).  
Therefore, when construction processes expose bare earth by eliminating vegetative 
cover, soils become much more vulnerable to erosion than in their natural state.  The 
erosion process is then greatly accelerated when a rainfall event occurs.  According to the 
Alabama Soil and Water Conservation Committee, ?erosion accelerated by the 
disturbances of humans, through agricultural and non-agricultural uses of the land, has 
caused several inches of erosion over the last 100 to 150 years, a comparatively short 
period? (Alabama Soil and Water Conservation Committee, 2003a).   
 3
Though wind and snow induced erosion is an important consideration, water-
related erosion from rainfall events is the largest problem in developing areas of Alabama 
(Alabama Soil and Water Conservation Committee, 2003a).  During a rainfall event, 
erosion is caused by the detachment of soil particles due to the impact of rain droplets 
and the shear stress of surface runoff.  Once the sediment is detached, it is transported 
downslope by overland flow and deposited into downstream water bodies.  This 
sediment, which will eventually settle out of suspension as the velocity of the water 
decreases, greatly impairs the natural aquatic habitat of the receiving water bodies.  
Therefore, the need for good erosion and sediment control alternatives is critical for 
maintaining the health of the aquatic environment. 
1.3  BEST MANAGEMENT PRACTICES (BMPs) 
Several types of best management practices (BMPs) are currently being used to 
minimize environmental damages caused by eroded sediment from construction sites.  
These BMPs include structural and nonstructural measures and can be classified by two 
basic categories.  The first category of BMPs is used for surface stabilization to prevent 
the erosion process from occurring and the second category is used for sediment control 
to minimize the eroded sediment from leaving the construction site.  Examples of surface 
stabilization BMPs listed by the Alabama Soil and Water Conservation Committee 
(2003a) include: i.) chemical stabilization, ii.) erosion control blankets (ECBs), iii.) 
groundskeeping, iv.) mulching, v.) permanent seeding, vi.) preservation of vegetation, 
vii.) retaining walls, viii.) shrub, vine, and groundcover plantings, ix.) sodding, x.) 
temporary seeding, and xi.) tree planting on disturbed areas.  Examples of sediment 
 4
control BMPs listed by the Alabama Soil and Water Conservation Committee (2003a) 
include: i.) block and gravel inlet protection, ii.) brush/fabric barriers, iii.) excavated drop 
inlet protection, iv.) fabric drop inlet protection, v.) filter strips, vi.) floating turbidity 
barriers, vii.) rock filter dams, viii) sediment barriers / silt fence systems, ix.) sediment 
basins, x.) straw bale sediment traps, and xi.) temporary sediment traps.  The BMPs listed 
above can be very effective in controlling nonpoint source pollution if designed and 
installed correctly and maintained regularly. 
In this research two of the abovementioned BMPs were evaluated to determine 
their effectiveness as erosion and sediment control technologies.  The first BMP 
investigated was the sediment control measure known as a silt fence tieback (a.k.a. ?j-
hook?) system.  A silt fence tieback system is created by turning the downslope end of 
the linear silt fence back into the fill slope and extending the fence up the slope to an 
elevation higher than the top of the fence at the toe of the slope.  This creates temporary 
detention basins that impound stormwater runoff during a rainfall event allowing 
suspended sediment to settle out of suspension.  These systems were previously studied 
on an intermediate-scale model by Halverson (2006) and the results showed that a well 
designed silt fence tieback system can remove up to approximately 90% of the total 
suspended solids (TSS) transported in the surface runoff.   
The second BMP investigated in this research was the use of anionic 
polyacrylamide (PAM).  PAM, which is considered a chemical stabilization BMP, is a 
negatively charged polymer chain that is applied to the soil surface to maintain the soil 
structure and prevent erosion.  PAM also serves as a binding agent for soil particles that 
are detached during erosion.  The flocculation of fine particles caused by the PAM allows 
 5
suspended sediment to settle out of suspension rapidly due to their increased particle size.  
This process suggests that PAM can not only serve as an erosion control BMP but also as 
a sediment control alternative if used in conjunction with other sediment control BMPs 
that impound surface runoff. 
1.4 RESEARCH OBJECTIVES 
This research was divided into two components to evaluate and test two potential 
erosion and sediment control BMPs that are used in the highway construction industry.  
The first component developed a method to quantify the effectiveness of silt fence 
tieback (a.k.a. ?j-hook?) systems as a sediment control BMP.  The second component 
focused primarily on the use of anionic PAM as a surface stabilization BMP to prevent 
erosion on highway construction sites.  The effect of PAM as a sediment control BMP 
was also briefly investigated.  The specific objectives of these two components are 
described in the following sections: 
Component 1: Silt Fence Tieback Systems 
1. Develop a computational method to determine the storage capacity of a silt fence 
tieback system. 
2. Develop a Visual Basic (VBA) coded spreadsheet design tool for practitioners to 
use in the construction industry that predicts the volume of stormwater runoff 
generated from a user specified rainfall event and provides design guidance for a 
tieback configuration to accommodate the generated stormwater runoff. 
3. Use the tool to design a tieback system on a local construction project and 
evaluate its performance over time during a case study. 
 6
Component 2: Anionic Polyacrylamide (PAM)   
1. Perform intermediate-scale physical experiments to determine the effectiveness of 
dry granular PAM applied to a typical 3H:1V slope for erosion control. 
2. Determine whether PAM, when used for erosion control, can also provide 
sediment control benefits by decreasing the settling time of suspended solids in 
the surface runoff. 
3. Provide recommendations for future erosion and/or sediment control testing using 
PAM. 
1.5 ORGANIZATION OF THESIS 
This thesis is divided into five chapters which document the efforts taken to 
complete the objectives of this research.  Following this chapter, Chapter 2:  Design of 
Silt Fence Tieback Systems, is a continuation of the work performed by Halverson 
(2006).  This chapter outlines the importance of determining the storage capacity of a silt 
fence tieback system and summarizes a computational procedure to do so.  The chapter 
also describes the procedures used to develop a Visual Basic (VBA) coded spreadsheet 
design tool that can be used by practitioners to design silt fence tieback systems to 
accommodate a user specified rainfall event.  Chapter 2 concludes by providing an actual 
case study where the design tool was used to determine a tieback configuration for an 
Alabama Department of Transportation (ALDOT) construction site.  A linear silt fence 
system was also installed at this site and the performance of the two systems were 
compared over four rainfall events.  Chapter 3: Literature Review: Use of PAM as an 
Erosion and Sediment Control BMP, introduces the application of anionic 
 7
polyacrylamide (PAM) as an erosion and sediment control alternative.  Also discussed in 
this chapter are the important variables to consider when selecting a PAM product and 
previous research on PAM as an erosion and sediment control technology.  Chapter 4: 
Intermediate-Scale Erosion Control Experiments Using PAM, outlines the development 
details of an intermediate-scale experimental model used for evaluating PAM as an 
erosion and sediment control technology, the experimental design used for the research, 
the data collection procedure, and the results from the experiments.   Chapter 5: 
Conclusions and Recommendations, provides some insights on the use of PAM as an 
erosion and sediment control technology and recommendations for future research using 
PAM.   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 8
CHAPTER TWO 
DESIGN OF SILT FENCE TIEBACK SYSTEMS 
2  
2.1 INTRODUCTION 
The pollution of water bodies due to sediment transported from poorly managed 
construction sites is an important environmental problem.  This transported sediment can 
dramatically alter or even destroy the aquatic habitat of the water bodies in which it is 
deposited.  To address this issue, a common practice in the construction industry is the 
installation of silt fence systems.  Silt fence systems are composed of a geotextile filter 
fabric that is sometimes supported by wire mesh and is fastened to either wooden or steel 
posts for structural support.   Their primary purpose is to serve as a sediment barrier 
where sheet flow can be detained allowing sediment to settle out of suspension.  These 
fences are usually installed around the perimeter of a construction site and often serve as 
the final barrier to capture sediment before leaving the site.     
 Traditionally, silt fence systems are installed as long, linear sections, but recent 
research suggests that tying the fence back into the contour at intermittent intervals and 
creating small detention basins is actually a much more effective design (Barrett et. al., 
1995; Robichaud et. al., 2001; Stevens et. al., 2004; Zech et. al., 2006).  This silt fence 
tieback design, commonly referred to as ?j-hooks?, can be an effective solution to 
controlling nonpoint source pollution on highway construction sites if designed and 
installed correctly.  A silt fence tieback system is created by turning the downslope end of 
the linear silt fence back into the fill slope and extending the fence up the slope to an 
elevation higher than the top of the fence at the toe of the slope.  This prevents 
stormwater runoff from passing around the toe of the fence and forces it to flow through 
the fence at the bottom of the fill slope.   These systems should only be used when there 
is runoff flow both down the fill slope and longitudinally in the direction of the road as 
shown in Figure 2.1.  The figure illustrates a properly designed silt fence tieback system 
on a highway construction site.  Halverson (2006) provided experimental data to describe 
the efficiency of this design. 
 
 
Figure 2.1  Silt Fence Tieback System 
 
 9
 10
In this effort, we will outline an analytical method for determining the storage 
capacity of a silt fence tieback system and provide design guidance to practitioners in the 
proper design of a tieback system using a spreadsheet design tool.  By using the 
computational procedures presented in this chapter, practitioners will be able to design 
silt fence tieback systems that will more effectively reduce sediment and other 
stormwater pollutant loads leaving highway construction sites.  
2.2 STORAGE CAPACITIES OF SILT FENCE TIEBACK SYSTEMS 
 When designing silt fence tiebacks, one of the most important factors to consider 
is the storage capacity of the system.  This storage capacity is critical in determining an 
effective tieback design that can accommodate a design rainfall event.  Important 
parameters that determine the storage capacity of a tieback system include the height of 
the fence above the existing ground (H
1
), existing ground width (L
1
), existing ground 
slope (S
1
), road fill slope (S
2
), ditch slope (S
3
), and the linear length of fence between 
tiebacks (L
FENCE
).    Figure 2.2 shows one typical silt fence tieback section incorporating 
the parameters that are considered when designing a tieback system.  During a rainfall 
event, the tieback section shown in Figure 2.2 serves as a temporary storage area to 
detain stormwater runoff.  The temporary detention of stormwater runoff allows sediment 
and other transported pollutants to be retained on site due to particles settling out of 
suspension.  This deposition process will lead to higher quality of water leaving the 
construction site since it contains less suspended sediment.   
 
 
Figure 2.2  Typical Silt Fence Tieback Section. 
 
 11
 As illustrated in the figure, the storage capacity of the silt fence is a critical 
component that needs to be considered while designing an effective system.  For a heavy 
rainfall event where the runoff volume exceeds the storage capacity behind the fence, the 
tieback system will experience an overtopping condition.  This scenario can be result of 
improper tieback spacing, poor silt fence installation practices, or an unforeseen rainfall 
event exceeding the design storm.  Therefore, the procedure for calculating the storage 
capacity of silt fence tieback systems is a critical design consideration and will be 
discussed in the following sections.  First, the discussion will focus on the mathematical 
procedures used to determine the maximum storage capacity required for a specified 
rainfall event along with the associated tieback spacing for a silt fence tieback system to 
satisfy the stormwater demand.  Next, the discussion will focus on an alternative design 
procedure developed to determine tieback storage capacities if the designer opts to install 
and configure the tiebacks more frequently where only a portion of the maximum storage 
 12
capacity is utilized.  The goal of this research is to develop a comprehensive 
understanding of the design and performance of a silt fence tieback system. 
2.2.1 Maximum Storage Capacity Calculation Procedure 
 The maximum storage capacity and associated intermittent tieback spacing are 
critical parameters in the design of effective silt fence tieback systems.  An ideal, cost 
effective system is one that uses the least amount of tiebacks required while still being 
capable of accommodating the stormwater runoff generated by the design rainfall event.  
The reasoning behind the ideal system is that it is assumed that the cost and work 
required for the installation of a silt fence tieback system increases as tieback frequency 
increases.  Figure 2.1, mentioned previously, illustrates a silt fence tieback system 
configuration where the maximum storage capacity is utilized by each tieback.  
 To determine the maximum storage capacity for a silt fence tieback, the available 
storage volume behind the fence was solved analytically.  The available storage volume 
behind the fence was divided into two components consisting of:  (1) the fill slope 
storage volume (V
1
), and (2) the existing ground storage volume (V
2
) as shown in Figure 
2.3.  The total available storage volume was then calculated by evaluating the two 
components separately and combining the results.   The origin (0, 0, 0) was set at the 
existing ground on the downslope end of the silt fence installation as shown in Figure 2.3. 
 
 
 
 
 
Figure 2.3  Total Storage Volume. 
2.2.1.1 Fill Slope Storage Volume (V
1
) 
 The first step in computing the volume stored on the fill slope (V
1
) was to 
determine the equations for the four boundary planes (Planes 1-4) that define V
1
.  The 
establishment of the defined coordinate system allowed Planes 1 through 3 to be easily 
determined.  The volume V
1
 along with points A, B, C, and D which define Planes 1 
through 4 are shown in Figure 2.4.   
 
Figure 2.4  Volume Stored on Fill Slope (V
1
). 
 
 
 13
The equations for Planes 1 through 3 are shown below as: 
? Plane 1:  x = 0; 
? Plane 2:  y = L
1
; 
? Plane 3:  z = H
1
. 
 The equation for the fourth plane of the system (Plane 4), which represents the fill 
slope, was not easy to define.  The first step in determining the equation for Plane 4 was 
to determine the coordinates of nodes B, C, and D as shown below: 
? B = (0, L
1
, L
1
S
1
); 
? C = (0, (H
1
 ? L
1
S
1
) / S
3
 + L
1
, H
1
); 
? D = ([(H
1
 ? L
1
S
1
) / S
3
], L
1
, H
1
). 
The normal vector (n) to Plane 4 was then determined from the established points by 
taking the cross product of vectors BC
JJJG
 and BD
JJJG
.  The equation for the normal vector (n) 
is shown in equation 2.1 below. 
 ckbjaiBDBCn ++=?=   (2.1)  
  
where, 
()
111
111
2
HLS
aH
S
???
=?
??
??
LS 
()
111
111
3
HLS
bH
S
???
=?
??
??
LS 
   
111 111
32
HLS HLS
c
SS
??????
=?
????
????
 
 14
Using the normal vector (n) and point B, the scalar equation for Plane 4 was determined 
and is shown in equation 2.2. 
 0)()()0(
111
=?+?+? SLzcLybxa  (2.2) 
Equation 2.2 was rewritten in terms of elevation (z) and is shown in equation 2.3. 
 
c
cSLbLbyax
z
111
++??
=  (2.3) 
 With all of the boundary planes defined, the volume V
1 
of the tetrahedron shown 
in Figure 2.4 was computed using triple integration.  The limits of integration in the z-
direction were defined by Plane 3 (z = H
1
) and Plane 4 (z = (-ax ? by + L
1
b + L
1
S
1
c) / c) 
while the limits of integration for the x and y directions were determined from the 
projection of the tetrahedron on the x-y plane shown in Figure 2.5.   
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?=
3
111
2
111
S
SLH
S
SLH
m
y 
L
1 
x 
(H
1
-L
1
S
1
)/S
2
 + L
1 
(H
1
-L
1
S
1
)/S
3
0
 
1
2
111
L
S
SLH
mxy +
?
+=
where,
 
 
Figure 2.5  Projection of V
1
 in the x-y Plane. 
 
 As shown in Figure 2.5, the limits of integration in the y-direction were y = mx + 
(H
1
 ? L
1
S
1
)/S
2
 + L
1
 and y = L
1
.  The limits of integration in the x-direction were x = (H
1
 ? 
 15
L
1
S
1
)/S
3
 and x = 0.  The triple integral used to compute V
1
 is shown in equation 2.4 and 
the solution is shown in equation 2.5. 
 
?? ?
?
+
?
+
++??
=
3
111
1
2
11
1
1
111
0
1
S
SLH
L
S
SLH
mx
L
H
c
cSLbLbyax
dzdydxV
 (2.4) 
 
()
?
?
?
?
?
?
?
? ?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
? ?
+?
?
+
?
?
?
?
?
?
?
? ?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
? +
?
++
?
?
?
?
?
?
?
? ?
?
?
?
?
?
?
?
? +
=
3
111
2
2
111
111
2
111
2
3
11111
2
1111
3
3
111
2
1
2
2226
2
S
SLH
S
SLH
c
b
SLH
S
SLH
S
SLHmSL
c
bma
S
SLHmH
S
SLH
c
bmam
V
 (2.5) 
2.2.1.2 Existing Ground Storage Volume 
 The volume stored on the existing ground (V
2
) is shown in Figure 2.6 below.   
 
 
Figure 2.6  Maximum Storage Volume on Existing Ground (V
2
). 
 
In order to determine V
2
, a relationship of how the cross-sectional area (A) in the x-z 
plane changes with respect to y was determined.  This relationship was easily defined 
since the cross-section is triangular in shape.  Using Figure 2.6 as a reference, an equation 
for the cross-sectional area (A) with respect to the y-direction was written as the 
following: 
 16
 ()
?
?
?
?
?
?
?
? ?
?=
3
11
11
2
1
)(
S
ySH
ySHyA  (2.6) 
 The volume V
2
 was then determined by simply integrating equation 2.6 for the 
entire existing ground length of y = 0 to y = L
1
.  This integral is shown in equation 2.7 
below as: 
 ()
? ?
?
?
?
?
?
?
? ?
?=
1
0
3
11
112
2
1
L
dy
S
ySH
ySHV  (2.7) 
The solution to the integration of equation 2.7 is shown below in equation 2.8 as: 
 
?
?
?
?
?
?
?
?
+?=
3
3
1
2
1
3
2
111
3
1
2
1
2
32
1
S
LS
S
LSH
S
LH
V  (2.8) 
2.2.1.3 Maximum Storage Capacity (V
T
) and Associated Tieback Spacing 
 The maximum storage capacity of a silt fence tieback was found by combining 
equation 2.5 and equation 2.8.  The expression for the maximum storage capacity (V
T
) is 
shown in equation 2.9.   
 
()
?
?
?
?
?
?
?
?
+?+
?
?
?
?
?
?
?
? ?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
? ?
+?
?
+
?
?
?
?
?
?
?
? ?
?
?
?
?
?
?
?
?
??
?
?
?
?
? +
?
++
?
?
?
?
?
?
?
? ?
?
?
?
?
?
?
?
? +
=
3
3
1
2
1
3
2
111
3
1
2
1
3
111
2
2
111
111
2
111
2
3
11111
2
1111
3
3
111
2
32
1
2
2226
2
S
LS
S
LSH
S
LH
S
SLH
S
SLH
c
b
SLH
S
SLH
S
SLHmSL
c
bma
S
SLHmH
S
SLH
c
bmam
V
T
 
  (2.9) 
The equation for the tieback spacing that will provide the maximum storage capacity is 
shown in equation 2.10.  This relationship, which was determined from the geometric 
properties of the total storage volume shown in Figure 2.3, is strictly a function of the 
height of the silt fence above ground (H
1
) and the ditch slope (S
3
).  
 17
 
1
3
FENCE
H
L
S
=   (2.10) 
By using equations 2.9 and 2.10 during design, practitioners will have a better 
understanding of the required tieback frequency and the maximum available storage 
capacity associated with the system on their project site.    
2.2.2 Storage Capacities for More Frequent Tieback Configurations 
 There are instances when a practitioner may decide to use a tieback spacing less 
than the spacing that provides the maximum storage capacity.  Therefore, the equations 
for the maximum storage capacity outlined in the previous sections were modified to 
determine the storage capacities of more frequent tieback configurations.  There are two 
possible situations that can occur if a shorter length of linear fence between tiebacks is 
utilized.  The first situation occurs when the linear length of fence between tiebacks is 
long enough to utilize the entire available storage capacity on the fill slope but only a 
portion of the available storage capacity on the existing ground.  The second situation is 
where the linear length of fence between tiebacks only uses a portion of both the storage 
capacity on the fill slope and the existing ground.  These two situations are shown in 
Figure 2.7 and Figure 2.8 and can be described mathematically as: 
(1)
3
1
3
111
S
H
L
S
SLH
FENCE
<?
?
, and (2)
3
111
S
SLH
L
FENCE
?
< .  The procedure for determining 
the storage capacities for scenarios (1) and (2) are outlined in the following sections. 
 18
 
Figure 2.7  Storage Volume for Scenario 1. 
 
 
Figure 2.8  Storage Volume for Scenario 2. 
 
2.2.2.1 Computational Procedure for Scenario 1 
 The volumes V
1
 and V
2
 for scenario 1, where
3
1
3
111
S
H
L
S
SLH
FENCE
<?
?
, were 
found by modifying the previously defined maximum storage capacity equations.  Under 
the first scenario, the total available storage capacity on the fill slope is still utilized; 
therefore, the equation for V
1
 is exactly the same as shown in equation 2.5.  V
2
, on the 
other hand, was found from analyzing Figure 2.6 through Figure 2.10.  Figure 2.6 and 
Figure 2.9 show the maximum and modified V
2
 while Figure 2.10 shows a cross-
sectional view of the maximum and modified V
2
.   
 19
x
z
y
(0,0,0)
L
1
H
1
S
3
S
1
D
A
B
V
2mod
 
 
Figure 2.9  Modified Storage Volume on Existing Ground (V
2modified
).
  
L
FENCE(modified)
H
1
S
3
L
FENCE(max)
= H
1
/S
3
 
 
Figure 2.10  Projection of Maximum and Modified Storage Volumes on Existing 
Ground (V
2
). 
  
 The modified equation for V
2
 was determined using Figure 2.9 as a reference.  
The integral and solution for the modified V
2
 in scenario 1 are shown in equation 2.11 
and equation 2.12.   
 () ()dyL
S
ySH
SLySHdy
S
ySH
ySHV
FENCE
xL
FENCE
L
?
?
?
?
?
?
?
?
?
?
???
?
?
?
?
?
?
?
? ?
?=
??
3
11
0
311
0
3
11
112
11
2
1
2
1
  
  (2.11) 
 
 20
 
?
?
?
?
?
?
?
?
?
?
?
?
?
?
+++
??
?
?
?
?
?
?
?
?
?
+?=
1
2
3
3
1
32
12
1
2
1
11
2
1
2
3
1
11
3
2
1
3
3
1
2
1
3
2
111
3
1
2
1
2
3
2
2
1
32
1
xLL
S
LxS
LxSL
xLLHLx
S
S
HxL
S
H
S
LS
S
LSH
S
LH
V
FENCEFENCE
FENCE
  
  (2.12) 
where, 
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
=
3
111
3
1
3
1
S
SLH
S
H
L
S
H
x
FENCE
. 
The total storage capacity for a silt fence tieback section in scenario 1 is shown in 
equation 2.13. 
 
()
3 2
2
111 1 111 11 111
32
2
22
1 11 1 11 1 11 1 1 111 1 1
111
2233
2
1
11
3
2
6222
1
22
1
2
T
am bm H L S H m H L S a bm L S m H L S
V
cS c
3
23
H LS b H LS H LS H L HSL S L
HLS
ScSSS
H
xL H
S
?? ?????+? ?+ ?
??
=++?
?? ????? ??
??
?? ???? ?
???????
+?+ +?+
?????
?????
??
?
?
?
?
?
?
233
22 22 2
11 1 11 1
33
2
3
FENCE FENCE FENCE
SSx
xL HL xL L SxL L xL?+++
  
  (2.13) 
2.2.2.2 Computational Procedure for Scenario 2 
 The equations for V
1
 and V
2
 in scenario 2, where
3
111
S
SLH
L
FENCE
?
< , are very 
similar to the equations developed in scenario 1.  The equation for V
1
 was found by 
simply changing the upper limit of integration in the x-direction to the length of fence 
(L
FENCE
) or tieback spacing of interest.  The modified integral and solution for V
1
 are 
shown in equation 2.14 and equation 2.15. 
 21
 
111
11
2
111
1
1
0
FENCE
HLS
Lmx LH
S
ax by L b L S c
L
c
Vd
?
++
??+ +
=
?? ?
zdx
 (2.14) 
 
()
FENCE
FENCEFENCE
L
S
SLH
c
b
SLH
S
SLH
L
mSL
c
bma
S
SLHmH
L
c
bmam
V
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
? ?
+?
?
+
?
?
?
?
?
?
?
?
?
?
?
?
?
?
? +
?
++
?
?
?
?
?
?
?
? +
=
2
2
111
111
2
111
211
2
11113
2
1
2
2226
2
  (2.15) 
 The equation for V2 in scenario 2 was almost identical to the previous scenario 
except for one small difference.  The difference in scenario 2 was that x = 1 in the V
2
 
equation.  The equation for V
2
 is shown in equation 2.16.     
 ()
13
22
11112
2
2
1
LSLLSLLLHV
FENCEFENCEFENCE
??=   (2.16) 
The total storage capacity for a silt fence tieback section in scenario 2 is shown in 
equation 2.17 
 
()
13
22
1111
2
2
111
111
2
111
211
2
11113
2
2
2
1
2
2226
2
LSLLSLLLH
L
S
SLH
c
b
SLH
S
SLH
L
mSL
c
bma
S
SLHmH
L
c
bmam
V
FENCEFENCEFENCE
FENCE
FENCEFENCET
??+
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
? ?
+?
?
+
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
+?
++
?
?
?
?
?
?
?
? +
=
(2.17) 
2.2.3 Sensitivity Analysis 
A sensitivity analysis was performed to determine effects of the existing ground 
width (L
1
), existing ground slope (S
1
), road fill slope (S
2
), and ditch slope (S
3
) on the 
maximum storage capacity and associated tieback spacing of silt fence tieback systems.  
To determine the sensitivity of each of the parameters, the parameter of interest was 
 22
varied while all of the other parameters remained constant.  These results are shown in 
Figure 2.11 through Figure 2.14 below.  The silt fence height (H
1
) remained constant for 
the analysis.  
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
0 50 100 150 200 250 300 350
Silt Fence Length (ft)
Storage C
a
pacit
y
 
(gal)
6 ft. Existing Ground Width
3 ft. Existing Ground Width
No Existing Ground Width
 
Figure 2.11  Constant S
1
, S
2 
and S
3
; Varying L
1
. 
 
 
 23
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
0 50 100 150 200 250 300 350
Silt Fence Length (ft)
Storage C
a
pacit
y
 
(gal)
1% Existing Ground Slope
3% Existing Ground Slope
5% Existing Ground Slope
 
Figure 2.12  Constant L
1, 
S
2 
and S
3
; Varying S
1
. 
 
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
0 50 100 150 200 250 300 350
Silt Fence Length (ft)
Storage C
a
pacit
y
 
(gal)
3H:1V Fill Slope
4H:1V Fill Slope
5H:1V Fill Slope
 
Figure 2.13  Constant L
1, 
S
1 
and S
3
; Varying S
2
. 
 
 24
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
0 50 100 150 200 250 300 350
Silt Fence Length (ft)
Storage C
a
pacit
y
 
(gal)
1% Ditch Slope
3% Ditch Slope
5% Ditch Slope
 
Figure 2.14  Constant L
1, 
S
1 
and S
2
; Varying S
3
. 
 
As can be seen from Figure 2.11 through Figure 2.14, the most critical parameter 
affecting the maximum storage capacity and associated silt fence length between tiebacks 
is the ditch slope (S
3
).  As the value for S
3
 increases, the maximum storage capacity and 
associated tieback spacing decrease.  When any of the other parameters are varied, the 
maximum storage capacity changes but the silt fence length associated with the 
maximum storage capacity remains constant.  This proves that the silt fence length 
between tiebacks associated with the maximum storage capacity is purely a function of 
the height of the silt fence (H
1
) and the ditch slope (S
3
) as shown in equation 2.10.   
2.3 SILT FENCE TIEBACK CONFIGURATION DESIGN TOOL 
 25
 A Visual Basic (VBA) coded spreadsheet design tool was developed to assist 
practitioners in the proper design of silt fence tieback systems to be used on highway 
 26
construction sites.  The tool uses the mathematical concepts outlined previously in this 
chapter along with the Soil Conservation Service (SCS) Curve Number (CN) method to 
determine an adequate tieback spacing that will accommodate a user specified rainfall 
event.  The tool is composed of two components which are (1) the stormwater runoff 
component and (2) the silt fence storage capacity component.  The details of these two 
components are outlined in the following sections along with an actual field example 
where the design tool was used to determine an appropriate tieback configuration on an 
Alabama Department of Transportation (ALDOT) job site.  
2.3.1 Stormwater Runoff Volume Component 
The first component of the silt fence tieback design tool is the stormwater runoff 
volume component.  The stormwater runoff volume is computed in the design tool by 
multiplying the rainfall excess determined from the SCS Curve Number method by the 
drainage area of the roadway section.  Inputs of this component include a single storm 
precipitation depth over a 24-hour period, SCS Curve Numbers (CNs) for the roadway, 
shoulder, and fill slope, the length and width of the roadway, the roadway shoulder width, 
and the width from the shoulder to the right of way (ROW).  The single storm 
precipitation depth can be determined from the Technical Paper No. 40 Rainfall 
Frequency Atlas maps while the CNs, which are a function of the area?s hydrologic soil 
group, land use, and impervious area, are shown in Appendix A.  The length and width of 
the roadway, roadway shoulder width, and width from the shoulder to the ROW can be 
determined from either field measurements or construction plans.  The details of how the 
design tool computes the stormwater runoff volume by the SCS Curve Number method 
are outlined in the following paragraphs. 
The first step in the computation of the stormwater runoff volume using the SCS 
CN method is the determination of the total rainfall depth (P) and a weighted CN 
(CN
weighted
) for the entire roadway section.  P is specified in the design tool by the user 
and CN
weighted
 is computed using the CNs of the roadway, shoulder, and fill slope which 
are also specified by the user.  The computation for CN
weighted
 is shown in equation 2.18. 
 
?
=
=
n
i
watershed
ii
weighted
A
ACN
CN
1
 (2.18) 
where, 
 CN
i            
= Curve Number for each individual section (e.g. roadway, shoulder, fill        
       slope) 
A
i
           = drainage area of each section  
 A
watershed
 = total drainage area  
 
 Once P and CN
weighted
 have been determined for the roadway section, the rainfall 
excess (Q) is calculated from equation 2.19   
 
( )
()SIP
IP
Q
a
a
+?
?
=
2
  (2.19) 
where,  
 Q  = rainfall excess (in) 
 P = total rainfall depth (in) 
 I
a
  = initial abstraction (surface storage, interception, and infiltration prior to  
                     runoff; assumed to be 0.2S) 
 S  = storage parameter given by equation 2.20 
 
 10
000,1
?=
weighted
CN
S    (2.20) 
 27
Q is then multiplied by the drainage area of the roadway section to produce the total 
stormwater volume V
total
 that needs to be accommodated by the silt fence tieback system.  
The equation for V
total
 is shown in equation 2.21. 
 
*
12
watershed
total
QA
V =   (2.21) 
where,  
 V
total   
= total stormwater runoff volume (ft
3
) 
 Q  = accumulated runoff (in) 
 A
watershed
 = drainage area of the roadway section (ft
2
) 
 
2.3.2 Silt Fence Storage Capacity Computation 
 An adequate silt fence tieback configuration that can handle the total stormwater 
runoff volume given by equation 2.21 can be determined using the silt fence storage 
capacity component.  The inputs of this component include height of the silt fence above 
the existing ground (H
1
), existing ground width (L
1
), existing ground slope (S
1
), road fill 
slope (S
2
), and the ditch slope (S
3
).  These parameters are illustrated in Figure 2.2 shown 
previously.  Using these parameters along with the equations outlined in section 2.2, the 
storage capacity component can compute the total storage capacity for various tieback 
configurations at a specific ditch slope.  Figure 2.15 shows an example of the results as 
computed by the storage capacity component. 
 28
0
5,000
10,000
15,000
20,000
25,000
30,000
0 50 100 150 200 250 300 350
Silt Fence Length (ft)
To
tal Storag
e Volume (ga
l)
1% Ditch Slope
 
 
Figure 2.15  Silt Fence Storage Capacity for Various Tieback Configurations.
  
The data shown in Figure 2.15 illustrates the relationship between the linear 
length of silt fence between tiebacks and the total storage volume per tieback at a 
specified ditch slope.  As shown in the figure, the total storage volume increases as the 
silt fence length between tiebacks increases to a certain point.  The point at which the 
curve flattens out corresponds to the maximum storage capacity of the silt fence tieback.  
In the example output shown in Figure 2.15, the maximum storage capacity is at a silt 
fence length between tiebacks of 300 feet.  This means that any tieback spacing greater 
than 300 feet will have the same storage capacity as a tieback spacing of 300 feet at a 
ditch slope of 1%.   
Practitioners can use the output of the storage capacity component like the one 
shown in Figure 2.15 to design to a tieback configuration that can handle the runoff 
volume generated from equation 2.21.  For cost effectiveness and ease of installation, an 
 29
 30
ideal system is one that uses the least number of uniformly spaced tiebacks. To meet this 
criterion, designers should first consider using the tieback spacing given by equation 
2.10.  If the storage provided by this tieback spacing is not enough, the designer should 
then consider a more frequent tieback configuration. 
2.3.3 Case Study: Application of the Silt Fence Tieback Design Tool 
The silt fence tieback design tool discussed in this chapter was used to design a 
tieback system for a 2 in. design storm on an ALDOT highway construction site located 
in Auburn, AL.  The field test site was developed to illustrate the proper application of 
the design tool and test the effectiveness of a silt fence tieback design versus a traditional 
linear silt fence system.  The field test site was monitored over several rainfall events and 
the performance results were documented.     
2.3.3.1 Site Description 
 The field test site used for this research was located on an ALDOT highway 
construction site at Exit 57 off of I-85 in Auburn, AL.  This site contained an 
approximately 600 ft. symmetrical vertical curve section of road with a 3H:1V fill slope.  
For testing purposes, the road was divided into two sections using the crest of the curve 
as the division point.  Linear silt fence was installed on half of the roadway section and 
tiebacks were installed on the other half.  Figure 2.16 shows the field test site after 
installation of the two silt fence scenarios and the characteristics of the site are listed in 
Table 2.1. 
 
 
(a) View from South Side of Test Site (b) View from North Side of Test Site 
(c) Silt Fence Tieback Section (d) Linear Silt Fence Section 
 
Figure 2.16  Experimental Test Site. 
 
Table 2.1  Test Site Characteristics. 
Variable Value
Roadway Length (ft): 600 
Roadway Width (ft): 50 
Roadway CN: 82 
Fill Slope Gradient (%): 33.3 
Fill Slope CN: 82 
Distance from Road to ROW (ft): 50 
Riprap Ditch Slope (%): 5 
  
As can be seen from Table 2.1, the roadway length and width at the field test site 
were approximately 600 ft. and 50 ft. respectively.  The fill slope of the site was 3H:1V 
 31
and the riprap ditch at the bottom of the fill slope had approximately 5% gradient.  The 
distance from the edge of the road to the ROW was 50 ft. at the crest of the curve. The 
roadway was not paved at the time; therefore, a single CN value of 82 was used for the 
roadway and fill slope.   This CN value is representative of a dirt road with a Natural 
Resources Conservation Service (NRCS) Hydrologic Soil Group (HSG) classification of 
B.  The HSG B classification corresponds to a soil with a final infiltration rate ranging 
from 0.15 to 0.3 in/h.  Figure 2.17 shows a cross-section of the roadway at the crest of the 
curve.   
 
Figure 2.17  Cross-Section of Field Test Site Roadway. 
 
2.3.3.2 Tieback Design 
 In order to determine the tieback configuration for the field test site, the 
characteristics shown in Table 2.1 were entered into the design tool.  A roadway length of 
300 ft. was used instead of the entire roadway length of 600 ft. since a tieback design was 
used on only half of the site and a linear silt fence system was used on the remaining half.  
Figure 2.18 shows a screen capture of the design tool and results for this field test site.  
Further details on how to use the design tool are shown in Appendix B. 
 32
 
 
Figure 2.18  Silt Fence Design Tool Used for Test Site. 
 33
 34
 As shown in Figure 2.18, the design tool computed a total stormwater runoff 
volume of 12,131 gallons for the 2 in. design rainfall event.  To accommodate this runoff 
volume, three tieback configurations were considered.  The first tieback configuration 
was determined from equation 2.10 and consisted of five tiebacks spaced at 60 ft. 
intervals.  This scenario only provided 10,100 gallons of storage which was much less 
than the computed stormwater runoff volume.  The second tieback configuration 
consisted of six tiebacks spaced at 50 ft. intervals.  This scenario provided 12,060 gallons 
of storage.  Finally, the third scenario consisted of ten tiebacks spaced at 30 ft. intervals.  
The total storage volume for this scenario was 17,670 gallons.  For ease of application 
and cost effectiveness, the research team decided to use the second scenario consisting of 
six tiebacks spaced every 50 ft. even though the storage volume provided by this scenario 
was slightly less than the total stormwater runoff volume.  The reasoning behind this 
decision was that the benefit provided by the third scenario was not worth the extra time 
and money that it would take to install it.     
2.3.3.3 Tieback System Performance 
As highlighted previously in this chapter, the purpose of a silt fence tieback 
system is to create small detention basins using tiebacks that will impound stormwater 
runoff and allow suspended sediment to settle out of suspension.  If designed and 
installed correctly, the tieback sections will capture and contain sediment transported 
from their contributing drainage areas which will reduce the likelihood of a failure due to 
excessive sediment loading at a single location commonly seen in linear silt fence 
systems.   Failures of linear silt fence systems typically occur due to one of five failure 
 35
modes.  These failure modes were outlined by Halverson (2006) and include the 
following: 
1. The stormwater runoff is greater than the storage capacity of the silt fence 
which creates an overtopping condition. 
2. The toe of the fence is undercut due to erosion caused by stormwater runoff 
accumulating and flowing along the toe of the fence.   
3. The fence is not properly tied into the contour which allows sediment to pass 
around the fence onto adjacent property. 
4. A large amount of sediment accumulates on the face of the fence at a single 
location and causes a structural failure. 
5. Failure due to improper installation. 
To evaluate the performance of the tieback and linear silt fence systems at the test 
site shown in Figure 2.16, erosion pins were installed to measure sedimentation and the 
site was monitored over four rainfall events.  The erosion pins used at the site were two 
feet long and they were driven into the ground one foot.  Three rows of pins were 
installed with the first row was being placed along the fence at 10 ft intervals.  The 
second row was placed 5 ft. up the fill slope and the third row was placed 3 ft. upslope 
from the second row.  After each rainfall event, the distance from the top of each erosion 
pin to the ground was measured to determine the approximate amount of sedimentation 
and the site was investigated to determine if any of the five failure modes listed 
previously had occurred.  Multiple pictures were also taken to qualitatively compare the 
performance of the two systems.  The dates and corresponding rainfall depths for the four 
rain events used in the study are shown in Table 2.2. 
 36
Table 2.2  Rainfall at Test Site. 
 
Date Rainfall Depth
(in) 
2/13/2007 1.0 
2/21/2007 0.5 
2/25/2007 0.4 
3/1/2007 2.5 
 
 Due to wide spacing of the erosion pins, measurable sedimentation for both 
systems could only be obtained along the fence; however, the pictures taken provided 
valuable insight to the effectiveness of the tieback design.  After the first three rainfall 
events, the pictures of the tieback system show that the tiebacks performed as expected 
by impounding stormwater runoff from their contributing drainage areas which allowed 
suspended sediment to settle out of suspension.  This is evident from the visible mud line 
along the fence at the downslope end of the tieback sections 3, 4, and 5 shown in Figure 
2.19.  The temporary detention basins created by the tieback system also distributed the 
total sediment load throughout the system and prevented erosion along the toe of the 
fence by not allowing concentrated flow to travel in long distances along the fence.  This 
is illustrated by the sedimentation profile along the fence shown in Figure 2.20.  There 
was not a single location where ground profile along the fence after the first three rainfall 
events eroded below the ground profile before installation of the tieback system.  The six 
tieback sections after the first three rainfall events are shown in Figure 2.19 and a profile 
of the ground along the fence is shown in Figure 2.20. 
 
 
 
(a) Section #1 (b) Section #2 
 
(c) Section #3 (d) Section #4 
 
(e) Section #5 (f) Section #6 
 
Figure 2.19  Six Tieback Sections After First Three Rainfall Events. 
 
 
 
 37
-5
0
5
10
0 50 100 150 200 250 300
Distance (ft)
Se
dime
nta
t
io
n (in
)
Ground Profile Before Installation of Tiebacks
Ground Profile After First Three Rain Events
Ground Profile After Fourth Rain Event
Tieback #1 Tieback #2 Tieback #3 Tieback #4 Tieback #5 Tieback #6
 
Figure 2.20  Sedimentation Profile Along the Fence of the Tieback System. 
 
The fourth rainfall event that occurred during the research effort was much larger 
than the first three with a total rainfall depth of 2.5 in.  This exceeded the design rainfall 
event for the tieback system by half an inch, but overall, the tieback system still 
performed as expected.  Four of the six tieback sections were in good shape but the fence 
in two of the sections experienced partial structural failure due to excessive loads caused 
by heavy sedimentation and impounded water during the rainfall event.  These near 
structural failures would not have occurred if the steel support posts of the silt fence 
system were closer together at the downslope end of the tieback sections.  Even though 
these sections nearly failed structurally due to excessive loads, they still captured the 
eroded sediment from their contributing drainage areas.  This can be seen from the heavy 
 38
 39
sedimentation shown in Figure 2.21 and from the sediment profile shown in Figure 2.20 
previously.  After this event, extra steel posts were installed at the potential failure 
locations to provide added structural support and prevent future structural failures from 
occurring.  During the very heavy fourth rainfall event, there were still no instances of 
erosion along the toe of the fence.  The six tieback sections after the fourth rainfall event 
are shown in Figure 2.21. 
 
 
 
 
 
 
 
 
 
 
 
 
 
(a) Section #1 (b) Section #2 
(c) Section #3 (d) Section #4 
(e) Section #5 (f) Section #6 
 
Figure 2.21  Six Tieback Sections After the Fourth Rainfall Event. 
 
 The linear system, on the other hand, performed much differently than the 
tieback system.  After the first three events, the linear system had the heaviest 
 40
sedimentation at a single location along the downslope end of the fence and erosion along 
the toe of the fence.  This erosion, which was caused by stormwater runoff accumulating 
and flowing along the fence, exposed the toe of the fence in multiple upslope areas and 
could potentially lead to a system failure in the future.  The concentrated sedimentation, 
though not a problem after the first three events, could also lead to a future failure in an 
event where more sedimentation occurs.  The pictures of the linear system after the first 
three events are shown in Figure 2.22 through Figure 2.25 and the sedimentation profile 
along the fence is shown in Figure 2.26.  
 
Figure 2.22  Upslope End of Linear 
Silt Fence w/ Little Sedimentation. 
 
Figure 2.23  Downslope End of Linear 
 Silt Fence w/ Heaviest Sedimentation. 
 
 
 41
  
Figure 2.24  Exposed Toe of Fence #1. Figure 2.25  Exposed Toe of Fence #2. 
 
-5
0
5
10
0 50 100 150 200 250 300
Distance (ft)
Se
d
i
me
nt
at
ion (i
n)
Ground Profile Before Installation of Linear Silt Fence
Ground Profile After First Three Rain Events
Ground Profile After Fourth Rain Event
Downslope End of Fence
Erosion Along the Toe of the Fence
Scour Hole
 
Figure 2.26  Sedimentation Profile Along the Fence of the Linear System. 
 
The performance of the linear system during the fourth event was similar to its 
performance for the first three events.  There was an obvious migration of sediment 
 42
towards the downslope end of the fence and toe of the fence was exposed even more at 
multiple upslope areas.  One difference during the fourth event, though, was that a scour 
hole developed at the downslope end of the system and undercut the fence.  This was 
probably due to the high velocity concentrated flow that occurred along the fence during 
the storm.  When the high velocity flow reached the lowest point in the system, the shear 
stress caused by flow exceeded that of the underlying soil which resulted in a scouring 
effect.  Pictures of the location of the scour hole before and after the fourth event are 
shown in Figure 2.27 and Figure 2.28 and the scour hole is also illustrated in the 
sedimentation profile shown in Figure 2.26 previously.  Additional pictures of the linear 
system after the fourth storm are shown in Figure 2.29 through Figure 2.32. 
  
Figure 2.27  Before Scour Hole at 
Downslope End of Linear Fence. 
Figure 2.28  Scour Hole at Downslope 
End of Linear Fence. 
 
 
 43
  
Figure 2.29  Upslope End of Linear 
Fence w/ Little Sedimentation After 
Fourth Storm. 
Figure 2.30  Downslope End of Linear 
Fence w/ Heavy Sedimentation After 
Fourth Storm. 
 
  
Figure 2.31  Exposed Toe of Fence After 
Fourth Storm. 
Figure 2.32  Exposed Toe of Fence After 
Fourth Storm. 
 
The sedimentation profiles and pictures shown in this section illustrate that both 
the silt fence tieback and linear systems performed as expected.  The tieback system 
performed as expected by distributing the total sediment load between the six tieback 
sections and preventing erosion from occurring along the toe of the fence.  The linear 
system, on the other hand, experienced concentrated flow along the fence which led to 
heavy sedimentation and scouring at the downslope end of the system and erosion along 
the toe of the fence at many upslope locations.  This system, if not maintained after future 
 44
 45
events, will eventually fail due to one or more of the modes discussed previously by 
Halverson (2006).  The research team will continue to monitor this site during future 
rainfall events to quantitatively and qualitatively show that silt fence tieback designs are 
much more effective in controlling sediment and reducing system failures than traditional 
linear silt fence installations. 
2.4 CONCLUSION 
 Sediment from poorly managed construction sites is a major environmental 
problem facing society today.  This problem, though, can be addressed and prevented if 
the proper abatement procedures are designed and installed correctly.  One such 
abatement method is the use of silt fence tieback systems.  These systems serve as 
temporary sediment basins that promote the impoundment of construction site runoff 
allowing sediment and other suspended solids to settle out of suspension.  By using the 
computational methods presented in this chapter, silt fence tieback systems can be 
designed correctly to effectively impound stormwater runoff, capturing sediment which 
will lead to a decrease in the amount of sediment leaving construction sites in the future.  
This containment of sediment on construction sites will help increase the integrity of our 
nation?s water bodies and lead to a much healthier aquatic environment. 
 
 
 
 
 
 46
CHAPTER THREE 
LITERATURE REVIEW: USE OF PAM AS AN EROSION AND SEDIMENT 
CONTROL BMP   
3  
3.1 INTRODUCTION 
One potential method for preventing erosion on highway construction sites is the 
use of anionic polyacrylamide (PAM).  PAM is a water soluble, negatively charged 
polymer chain that serves as a binding agent for soil particles.  Typically, PAM is used in 
conjunction with ground cover practices such as seeding and mulching to promote soil 
structure and stability.   The ground cover practices serve as the protection against 
detachment due to rain drop impact while the PAM serves as a soil stabilizing agent 
which maintains the soil structure and promotes infiltration.  McLaughlin (2006) suggests 
that PAM should never be applied alone but always in conjunction with ground cover 
practices.  Other studies have shown though that PAM applied to slopes without ground 
cover can serve as an effective erosion control alternative (Flanagan et al., 1997a, b; 
Flanagan et al., 2002a, b; Peterson et al., 2002; Roa-Espinosa et al., 1999).  These 
conflicting results along with the conclusions of many other studies will be reviewed and 
discussed in this chapter.  
 47
The primary goal of this research was to determine from previous studies and our 
own research if PAM without ground cover can be an effective erosion control 
technology for highway construction sites where steep slopes are common.  A secondary 
goal of this research was to determine whether PAM used for erosion control can also 
provide sediment control benefits by decreasing the settling time of suspended solids in 
surface runoff waters.    
3.2 POLYMERS USED FOR EROSION AND SEDIMENT CONTROL 
Some research suggests that PAM can be a viable erosion and sediment control 
alternative on construction sites if used correctly.  This section will give an overview of 
PAM including the important variables to consider when selecting a polymer product, the 
different application methods of polymer products, and previous research addressing the 
effectiveness of polymers as erosion and sediment control alternatives.   
3.2.1 Variables to Consider when Selecting a Polymer 
PAM can be purchased in many forms and each form has its advantages and 
disadvantages.  Four important variables to consider when selecting a polyacrylamide 
product are the i.) ionic strength, ii.) structure of the polymer, iii.) whether the 
polyacrylamide is in solid or liquid form, and iv.) the molecular weight.  These four 
variables will be outlined in the following paragraphs to give a better understanding of 
the various forms of PAM available and how to select the proper PAM product for a 
construction site.     
The first variable that should be considered in the PAM selection process is ionic 
strength or polymer charge.  PAM is available in cationic, anionic, and non-ionic form.  
 48
Cationic PAM is positively charged and has been found to work significantly well as a 
flocculent for clay particles and other negatively charged substances.  Currently, though, 
cationic PAM is proven to be environmentally harmful to aquatic habitat and therefore 
cannot be used in erosion and sediment control applications.  Non-ionic (neutral charge) 
and anionic (negatively charged) PAM, on the other hand, have been approved for 
erosion and sediment control applications and are considered environmentally safe as 
long as they contain less than 0.05 percent free acrylamide.  The non-ionic PAM is rarely 
used for erosion control due to its lack of interaction with charged soil particles, but 
anionic PAM has shown to be fairly effective in the control of sediment and erosion if 
used properly.  For erosion and sediment control, PAM is typically used in conjunction 
with ground cover techniques such as seeding and mulching to provide soil structure 
stability  
The next variable to consider when selecting a PAM product is the polymer 
structure.  PAM is available in linear, fully cross linked, and branched form.  These three 
polymer structures are shown in Figure 3.1.  The linear form has a long snake-like 
structure and is most widely used in stormwater runoff applications.  The fully cross 
linked form, on the other hand, has a net-like structure and is used in products such as 
diapers due to its water retaining capabilities.  Finally, the partly cross linked form has a 
branched structure and is used in municipal sewer sludge applications.  The polymer 
structure plays a very important role in its effectiveness for various applications and 
should be given considerable thought before choosing a PAM product.  For erosion 
control in the construction industry, the linear polymer structure is the most widely used 
and provides the most effective results.   
 
a.) Linear 
 
 
 
 
b.) Branched c.) Fully Cross Linked 
 
Figure 3.1  Polymer Structures 
 
The third variable to consider is if the PAM is in liquid or solid form.  There are 
advantages and disadvantages of both forms which should be considered in the product 
decision selection process.  The solid form of PAM is typically available in powder or 
bead form with a polymer content ranging from 85% to 90% in the powder form and 
about 95% in the bead form.  The powder form is cheaper than the liquid form and can be 
applied either in dry granular form or solution form mixed with water.  When applied in 
solution form, it has to be carefully mixed because the water mixing process can be very 
sensitive and can lead to problems.  When adding the solid granular PAM to water, it is 
important to introduce the granules slowly and under constant agitation.  This will help 
prevent the formation of large globules caused by the granules sticking together which 
are hard to dissolve.  The liquid PAM, on the other hand, is available as an inverse 
emulsion or dispersant with a polymer content ranging from 25% to 40% for emulsions 
and 50% for dispersants.  The remaining contents of the liquid PAM mixture are typically 
oils which can lead to some environmental problems if used in areas of slow moving or 
stagnant water bodies such as ponds and lakes. The liquid form is more costly than the 
powder form but it is easier to handle because the mixing process is not required.  The 
 49
 50
advantages and disadvantages regarding the product form outlined above are very 
important in determining which PAM product to use. 
The final variable that should be considered in the PAM selection process is the 
molecular weight.  The molecular weight of a PAM product is a direct reflection of the 
size of the molecule.  Therefore, as the molecular weight of the polymer increases, the 
size of the molecule also increases which leads to an increase in the number of bonding 
sites that are available along the polymer chain.  An increase in molecular weight also 
leads to an increase in viscosity.  The molecular weight of a PAM product cannot be 
directly measured due to limitations of current testing procedures; therefore, the PAM 
solution viscosity is commonly used for product comparison.  The abovementioned four 
concepts play a major role in the performance of a polymer in the environment and 
should be carefully considered when choosing a PAM product.   
3.2.2 Applying Polymers 
PAM applications come in many different forms and can be applied in a number 
of ways for slope stabilization.  The most common application methods of PAM are 
either applying it in the dry granular form or applying it as liquid solution using the dry 
granular form or liquid emulsion mixed with water.  PAM is usually applied in the dry 
granular form using a spreader or by hand, and it is typically used in conjunction with 
additives such as seed and fertilizer and ground cover practices such as straw and mulch.  
PAM as a liquid solution is also typically mixed with a combination of seeds and 
mulches but is applied using a hydroseeder.  When applying granular PAM using a 
hydroseeder, it is suggested by McLaughlin (2006) that approximately one pound of 
 51
PAM should be mixed per 100 gallons of water.  If used at higher rates, the PAM 
solution may become very viscous leading to problems during the application process.   
McLaughlin (2006) recommends that when applying granular PAM using a 
hydroseeder, the PAM should be added first and mixed for approximately 30 minutes 
with half a tank of clean water.  The seed and mulch should then be added to the mixture 
along with the rest of the water to produce the hydromulch or hydroseed plus PAM 
solution.  This solution can then be applied to the soil surface for erosion prevention.  The 
application rate of PAM per acre can vary greatly depending upon the steepness of the 
land, but it has been recommended that, for steep slopes (? 10%), 20 pounds per acre is a 
minimum dose that can provide effective results (McLaughlin, 2006).   
3.2.3 Previous Research on the Effectiveness of Polymers 
In the construction industry, anionic PAM is typically the only PAM product 
used; therefore, the rest of this research will focus solely on the use of anionic PAM.  
Previous research in this area has provided conflicting results; therefore, more research is 
needed to determine if PAM can be an effective erosion control alternative for the 
highway construction industry.  Most of the past research related to PAM was focused 
towards agricultural applications involving mildly sloped land (i.e. < 10%) (Flanagan et 
al., 1997a, b; Lentz et al., 2002; Bjorneberg et al., 2000; Shainberg et al., 1990).  Results 
from these studies have demonstrated the benefits of using PAM, but the recommended 
application rates may not provide effective results in the highway construction industry 
where slopes are generally steeper.  This was highlighted in research performed by Hayes 
et al. (2005) and McLaughlin and Brown (2006).  Other studies, though, have shown that 
 52
PAM applied to steep slopes (i.e. ? 10%) at higher application rates can serve as an 
effective erosion control alternative even when used without ground cover practices 
(Flanagan et al., 1997a, b; Flanagan et al., 2002a, b).  Results of these studies along with 
other research regarding the use of PAM as an erosion control technology are reviewed in 
the following sections.  
3.2.3.1 PAM Applied to Mild Slopes (i.e. < 10%) 
Flanagan et al. (1997a, b) evaluated the use of PAM as an erosion control 
technology under simulated rainfall conditions with an intensity of 64 mm/h.  The 
experiments were performed near West Lafayette, Indiana on a Russell silt loam soil that 
was disked prior to testing.  The research showed that PAM applied to fairly mild slopes 
of 6% to 9% at an application rate of 20 kg/ha significantly reduced runoff and sediment 
transport for the initial rain event.  For the following rain events, sediment transport was 
still reduced but there was no significant reduction in runoff. 
Shainberg et al. (1990) tested the effectiveness of PAM on a 5% slope using 
simulated rainfall with an intensity of 38 mm/h.  These results showed that infiltration 
rates nearly tripled when PAM was applied at rates of 20 and 40 kg/ha.  Other research 
on mild slopes using much lower application rates than the previous studies also showed 
the benefits of using PAM (Bjornberg et al., 2000; Lentz et al., 2002).  Bjornberg et al. 
(2000) tested the effectiveness of PAM applied to a Roza loam on a 2.4% slope.  The 
PAM was applied through sprinkler irrigation at rates of 2 and 4 kg/ha to bare soil and 
soil with straw cover.  Simulated rainfall with an 80 mm/h intensity and 15 minute 
duration was used for this research. The results show that PAM applied to a 70% straw 
 53
covered surface reduced runoff by 75% to 80% while PAM applied to the bare soil 
reduced runoff by 30% to 50%.  Lentz et al. (2002) applied PAM at a rate of 1.8 kg/ha in 
furrow irrigation water to a Portneuf silt loam at a 1.5% slope and found that sediment 
loss was reduced by an average of 82%.  Each irrigation process used for this research 
applied approximately 68 mm of water over a 12 hour period.  These studies show that 
PAM can be an effective erosion control alternative for mild slopes (i.e. < 10%).  
3.2.3.2 PAM Applied to Steep Slopes (i.e. ? 10%) 
We will now review research studies have evaluated the use of PAM on steeper 
slopes (i.e. ? 10%) commonly encountered on highway and other construction sites.  The 
studies include work completed by Hayes et al. (2005), McLaughlin and Brown (2006), 
Flanagan et al. (2002a, b), Peterson et al. (2002), and Roa-Espinosa et al. (1999).  Hayes 
et al. (2005) performed a study on three North Carolina Department of Transportation 
(NCDOT) job sites in the Piedmont and Coastal Plain areas to determine the effects of 
PAM when used alone and in conjunction with grass seeding and straw mulching 
applications.  They characterized the reduction in runoff volumes, turbidity levels, and 
sediment losses after natural rain events.  Two test sites were developed for the research 
effort in the Piedmont area and one test site was developed in the Coastal Plain area.  The 
Piedmont sites were developed on 20% and 50% slopes while the Coastal Plain site was 
developed on a 20% slope.  The two Piedmont sites received a total of 58 mm and 161 
mm of precipitation respectively over six storm events, and the Coastal Plain site 
received a total of 115 mm of precipitation over seven storm events.  At each of the sites, 
tests were completed with control plots consisting of bare soil (i.e. control), plots with 
 54
PAM only, and plots with PAM plus seed and mulch.  Two different PAM products, 
Solifix from Ciba Specialty Chemicals and Siltstop 705 from Applied Polymer Systems, 
were applied according to the application rates recommended by the manufacturer.  
These products were also applied at half of the recommended rates for comparative 
purposes.  The recommended application rate for Solifix and Siltstop 705 was 1.3 lb per 
acre and 9.3 lb per acre respectively.  
The results from the study show that the application of seed and mulch was 
effective in reducing the turbidity and sediment loss at the three test locations but the 
addition of PAM did not significantly have an effect on the results.  Neither the addition 
of PAM nor seed and mulch had an impact on the runoff volume from the three test 
locations.   The reason why PAM did not reduce the runoff volume, turbidity, and 
sediment loss may be due to the low application rates.    
Another study, performed by McLaughlin and Brown (2006), found similar 
results.  McLaughlin and Brown (2006) evaluated the effects of PAM on erosion control 
when used alone and in conjunction with four different types of ground cover practices 
commonly used in the construction industry.  The ground cover practices evaluated with 
and without PAM were straw, wood fiber, straw erosion control blankets (ECB), and 
mechanically bonded fiber matrix (MBFM).  PAM was applied for testing at a rate of 19 
kg/ha and control tests were also performed using bare soil plots.  These tests were 
performed using natural rainfall events on field plots and simulated rainfall on 1 m wide 
by 2 m long and 9 cm deep wooden boxes filled with soil. The field plots had slopes of 
4% and consisted of a Cecil silt loam material that was tilled prior to testing.  These field 
plots experienced five natural rainfall events totaling 148 mm over a 36 day period.  The 
 55
soil boxes, on the other hand, were sloped at 10% and 20% and three different soil types 
(sandy clay loam, sandy loam, loam) were used.  The soil boxes were loaded with 
approximately 140 kg of soil and leveled by hand with no further compaction.  Two tests 
were run on the soil boxes with the first test consisting of two consecutive rainfall events 
and the second consisting of four.  The simulated rainfall events produced a rainfall 
intensity of 3.4 cm/h and were run for five minutes after the start of surface runoff.   
The results from this study show that the use of ground cover practices 
significantly reduced the runoff volume, sediment loss, and turbidity in both the field 
plots and the soil boxes.  The application of PAM did not provide a significant benefit in 
most cases.  Exceptions were that it did increase vegetative cover overall, and it reduced 
turbidity on the field plots and in some cases on the soil boxes when used in conjunction 
with ground covers.  PAM also worked well in reducing the turbidity for the 20% slope 
for successive rainfall events.  This research concluded that, ?PAM at the 19 kg/ha rate 
does not always provide water quality benefits beyond that of a ground cover alone? 
(McLaughlin and Brown, 2006) and that additional testing needs to be performed.   
Other research was performed by Flanagan et al. (2002a) using higher application 
rates of PAM than used by McLaughlin and Brown (2006).  This research evaluated the 
effects of two soil treatments under simulated rainfall conditions on silt loam topsoil at a 
32% slope.  The two soil treatments included: (1) PAM with a charge density of 32% and 
a molecular mass of 20 Mg/mol applied at a rate of 80 kg/ha and (2) the same PAM 
treatment in conjunction with 5 Mg/ha of gypsum.  The PAM product used for this 
research was Percol 336 which is manufactured by Ciba Specialty Chemicals.  A bare 
soil control was also evaluated for comparative purposes.   
 56
 The three scenarios were tested on 2.96 m wide by 9.14 m long test plots and the 
experiments were replicated three times.  The plots were rototilled prior to testing 
producing a disturbed surface.  Three consecutive simulated rainfall events were used for 
the tests totaling 176 mm over 4.25 hours.  The first event produced a 25 year storm with 
a rainfall intensity of 69 mm/h for one hour duration.  The test plots were allowed to dry 
for an hour and a second event was simulated at the same intensity and duration as the 
first.  Finally, the plots were allowed to dry for thirty more minutes before being rained 
on for an additional 45 minutes.  The final 45 minutes of rain consisted of three 15 
minute events with intensities of 64 mm/h, 28 mm/h, and 100 mm/h respectively.  The 
cumulative rainfall event over the 4.25 hour period corresponds to a return period of 
greater than 100 years.   
 The results from the experiments show that the addition of PAM and PAM-and-
gypsum can be an effective solution for reducing erosion on steep slopes.  Overall, the 
PAM treatment reduced runoff by 40% and sediment yield by 83%, while the PAM-and-
gypsum treatment reduced runoff by 52% and sediment yield by 91%.  The added 
benefits from the addition of gypsum can be attributed to, according to Flanagan et al. 
(2002a), increased multivalent cation levels which reduced clay dispersion and improved 
the effectiveness of PAM.   In conclusion, Flanagan et al. (2002a) suggests that PAM soil 
amendments can provide a viable alternative for erosion control on steep slopes due to 
their effectiveness and cost versus other conventional erosion control techniques.   
 This conclusion was expanded upon in Flanagan et al. (2002b).  Flanagan et al. 
(2002b) studied the effects of PAM and PAM-and-gypsum on runoff, sediment yield, and 
vegetation establishment for steep slopes under natural rainfall conditions.  In this 
 57
research, test plots 2.96 m wide by 9.14 m long were established at two experimental test 
sites.  The first test site was at an Indiana Department of Transportation (INDOT) project 
on a clay loam highway cut slope with a 35% gradient, and  the second site was at a 
Waste Management, Inc. recycle disposal facility (RDF) on a silt loam landfill cap with a 
slope of 45%.  Three test plots were developed at the two sites consisting of a bare soil 
control plot, a plot with PAM only, and a plot with PAM-and-gypsum.  The same PAM 
and PAM-and-gypsum treatments from the previously mentioned study were used and 
the experiments were replicated three times.  The plots were tilled by a hand pick prior to 
testing to a depth of 4 to 5 cm.  Nine natural runoff-producing rainfall events totaling 214 
mm occurred over a two month period on the INDOT site while 17 runoff-producing 
events totaling 688 mm occurred over a five and a half month period on the RDF site.   
 The results from this study show that the use of PAM and PAM-and-gypsum can 
be an effective solution for reducing erosion and promoting vegetative growth on steep 
slopes.  At the INDOT site, sediment yield was reduced 54% from the PAM treatment 
and 45% from the PAM-and-gypsum treatment.  Runoff was also reduced at this site by 
an average of 33% for both treatments though runoff was not significantly reduced for the 
larger events where rainfall exceeded 25 mm.  This could have been due to very wet 
antecedent moisture conditions from previous rain events.  At the RDF site, sediment 
yield was reduced 40% and 53% respectively from the PAM and PAM plus gypsum 
treatments.  Runoff for this site was reduced by 15% for the PAM treatment and 28% for 
the PAM plus gypsum treatment when compared to the control.  The treatments though 
did not seem to have a significant effect for events with greater than 55 mm of rain.  This 
could probably be contributed to the high antecedent moisture conditions from previous 
 58
rain events.  The conclusions of  this research is similar to that found previously by 
Flanagan et al. (2002a) in that PAM can be a good alternative for erosion control on steep 
slopes.   
Other research that has shown PAM to be an effective alternative for erosion 
control was performed by Peterson et al. (2002).  Peterson et al. (2002) performed a field 
study using simulated rainfall to evaluate the effectiveness of the method of application 
of PAM (dry or liquid) and the effectiveness of a multivalent electrolyte (Ca
++
) source 
when used in conjunction with PAM.  According to Peterson et al. (2002), ?the benefits 
of PAM are enhanced by the introduction of an electrolyte source (multivalent cations) 
that helps to create a cation bridge for the polymer to absorb to the soil? (Peterson et al., 
2002).  To test this idea, there were three PAM treatments used in the research plus an 
untreated control.  The treatments included: (1) PAM in liquid solution plus Nutra-Ash, 
(2) granular PAM plus Nutra-Ash, and (3) PAM in solution with SoilerLime.  The PAM 
product used was Percol 336 which has a charge density of 32% and molecular mass of 
20 Mg/mol.  PAM was applied at a rate of 60 kg/ha for all treatments.  The Nutra-Ash 
and SoilerLime were applied at rates that produced the same amount of Ca
++
 as provided 
by the 5 Mg/ha of gypsum used in previous research by Chaudhari (1999).   
  The Peterson et al. (2002) study developed 12 - 3.0 m wide by 9.1 m long test 
plots using silt clay topsoil on a hillslope in West Lafayette, Indiana.  The average slope 
of the plots was 16.6% plus or minus 0.3%.  Each plot contained approximately 12 cubic 
meters of soil that was raked and leveled by hand with no further compaction.   The 
simulated rainfall events used for the experiments consisted of a combination of three 
successive storm events.  The first rainfall event had an intensity of 75 mm/h for a one 
 59
hour period.  The plots were then allowed to dry for an hour before the second rainfall 
event began.  The second event also had an intensity of 75 mm/h and duration of one 
hour followed by a 30 minute break.  The final 45 minutes of rain consisted of three 15 
minute events with intensities of 75 mm/h, 28 mm/h, and 100 mm/h respectively.  The 
cumulative rainfall event over the 4.25 hour period corresponds to a return period of 
greater than 100 years.   
 The results from this study show that PAM applied as a liquid solution in 
conjunction with a Ca
++
 source is much more effective in preventing erosion than PAM 
applied in dry granular form with a Ca
++
 source.  PAM applied in the liquid form reduced 
total runoff by 62% to 76% and sediment yield by 93% to 98% while the PAM applied in 
the dry granular form provided almost no benefit.  This research suggests that PAM can 
be an effective alternative for erosion control if applied in the liquid form with a Ca
++
 
source.  The effectiveness of PAM alone without a Ca
++
 source was not investigated in 
this study.   
The last research that will be discussed was performed by Roa-Espinosa et al. 
(1999).  In this study, four different soil treatments along with a bare soil control were 
tested on 1 m by 1 m plots on a 10% slope using simulated rainfall.  The four soil 
treatments included: (1) liquid PAM solution applied to dry soil, (2) dry granular PAM 
applied to dry soil, (3) liquid PAM solution with seeding and mulching applied to dry 
soil, and (4) liquid PAM solution applied to wet soil.  The PAM was applied at a rate of 
22.5 kg/ha and the soil type used for the tests was a Dodge silt loam.  A rainfall intensity 
of 6.4 cm/h was used, and the experiments were run for 40 to 50 minutes depending on 
the amount of runoff that was produced.    
 60
The results from this study show that all of the soil treatments significantly 
reduced the sediment yield of the test plots.  The worst soil treatment was the liquid PAM 
applied to wet soil, and it still reduced average sediment yield by 77%.  The PAM plus 
seeding and mulching provided the best results by reducing the average sediment yield by 
93%, and the dry PAM mix reduced the sediment yield by 83%.  Roa-Espinosa et al. 
(1999) concludes by stating, ?the ease of application, low maintenance, and relatively 
low cost associated with PAM make it a practical solution to the costly methods being 
implemented today? (Roa-Espinosa et al., 1999).     
3.3 SUMMARY 
Anionic PAM is a negatively charged polymer chain that can potentially serve as 
an effective erosion control abatement technology if properly used.  PAM is typically 
applied for slope stabilization in either a dry granular form using a spreader or as a liquid 
solution using a hydroseeder.  Ground cover practices, such as seeding and mulching, are 
commonly used in conjunction with the application of PAM and serve as protection 
against soil detachment due to rain drop impact.  The PAM product then acts as a soil 
stabilizing agent which maintains soil structure and reduces erosion.   
Previous research suggests, in many cases, that PAM can be an effective erosion 
control technology.  When used in agricultural applications on fairly mild slopes (i.e. < 
10%), PAM has proved to be very effective (Flanagan et al., 1997a, b; Lentz et al., 2002; 
Bjornberg et al., 2000; Shainberg et al., 1990).  When used on steeper slopes that are 
commonly encountered in the construction industry (i.e. ? 10%), there have been mixed 
results.  Hayes et al. (2005) and McLaughlin and Brown (2006) found that there was not 
 61
an added benefit from using PAM when compared to using straw and mulch.  This lack 
of benefits may be contributed to the low application rates (0.76 - 19 kg/ha) used in their 
studies.  Other studies using higher application rates (22.5 ? 80 kg/ha) found PAM to be a 
very effective erosion control technology even when used without ground cover 
techniques (Flanagan et al., 2002a, b; Peterson et al., 2002; Roa-Espinosa et al., 1999).  
 Of all the studies mentioned above, none were conducted with PAM on 
compacted slopes which are typical of highway construction sites.  All of the studies, 
instead, have dealt with uncompacted slopes that were usually tilled prior to PAM 
application.  The fact that uncompacted tilled slopes are not a realistic representation of 
slopes encountered on highway construction sites indicates the need for future research.  
This research should incorporate typical construction procedures and create a more 
realistic testing environment which can be applicable to the highway construction 
industry.  Issues that need to be addressed for compacted steep slopes include: (1) the 
effectiveness of PAM applied alone in the dry granular form, (2) the effectiveness of 
PAM applied alone as a liquid solution (3) the effectiveness of PAM when used in 
conjunction with ground cover practices, (4) the effectiveness of ground cover practices 
alone, and (5) the effectiveness of PAM on various soil types.  This research will attempt 
to address the first of these five issues in order to create a better understanding of the 
possible role of dry granular PAM when applied alone as an erosion control alternative 
on highway construction sites.  It is recommended that future research should address the 
remaining four issues.   
 62
CHAPTER FOUR 
INTERMEDIATE-SCALE EROSION CONTROL EXPERIMENTS USING PAM 
4  
4.1 INTRODUCTION 
Previous research suggests that PAM can be an effective erosion abatement 
technology if used properly.  To test this idea, intermediate-scale physical experiments 
were performed using dry granular PAM on a silty sand material.  Three scenarios were 
modeled including a bare soil control and PAM applied at rates of 20 and 40 lb/ac.  A 
series of three simulated rainfall events were used for the tests and each test was 
replicated three times.  The details of the intermediate-scale model, experimental design, 
and test results will be discussed in the following sections.  The results from this research 
will provide valuable insight on the effectiveness of granular PAM as an erosion control 
technology.  This research will also attempt to determine the effect of PAM on the 
settling time of suspended solids in surface runoff when applied as a surface stabilization 
BMP for erosion control.   
4.2 INTERMEDIATE-SCALE MODEL 
An intermediate-scale physical model of a highway construction site was 
previously developed at Auburn University by Halverson (2006) to study the
effectiveness of silt fence tieback systems as a sediment control technology.  This model 
was modified to meet the objectives of our study concerning PAM as an erosion control 
technology.  The original model developed by Halverson (2006) was a one-sixth scaled 
down version of a 48 ft. by 48 ft. roadway section from the centerline of the road to the 
ROW.  The model had a roadway deck and shoulder with a 2% cross slope, a 3H:1V fill 
slope, and a 2% existing ground section at the bottom of the slope.  A five nozzle rainfall 
simulator was attached to the model and the model was also sloped 2% in the 
longitudinal direction.  Further details of this design can be found in Halverson (2006).  
The original intermediate scale model as designed by Halverson (2006) is shown in 
Figure 4.1. 
 
 
Figure 4.1  Intermediate-Scale Model Designed by Halverson (2006).
 
 63
The model shown in Figure 4.1 was modified slightly to meet our research 
objectives.  We wanted to develop a model where multiple replications of the same 
scenario could be tested simultaneously.  Therefore, the road section was completely 
blocked off and the model was divided into three equal sections.  The modified design 
divided the previously 96 in. wide by 69 in. long by 6 in. deep fill slope section into three 
32 in. wide by 69 in. long by 6 in. deep soil plots.  A new six nozzle rainfall simulator 
was also designed and installed by the research team to replace the old five nozzle 
system.  The modified intermediate-scale model is shown in Figure 4.2 and the details of 
the model components are discussed in the following sections. 
 
Figure 4.2  Modified Intermediate-Scale Erosion Model. 
 64
 65
4.2.1 Soil Plot Design 
 The model shown in Figure 4.2 consisted of three identical soil plot sections.  
Each section had a 57 in. long fill slope with a 33.3% gradient and a 12 in. long existing 
ground section with a 2% gradient at the bottom of the fill slope.  The plots were 6 in. 
deep and had drains to collect both the surface runoff and infiltration.  Prior to testing, the 
plots were loaded with two 3 in. layers of fill materials.  The top 3 in. of the plots 
contained a compacted silty sand material.  A Unified Soils Classification System 
(USCS) classification was conducted on this material by Halverson (2006) and the 
material classified as a poorly graded sand (SP).  The bottom 3 in. consisted of a 
lightweight, porous Expanded Polystyrene (EPS) material that was overlaid with a 
SKAPS W200 Woven Geotextile Fabric.  The EPS material was used for the bottom 3 in. 
of the plots to reduce the overall load on the supporting structure caused by the weight of 
the material in the plots.  The EPS layer also had a very high hydraulic conductivity 
which allowed the research team to measure the amount of water that infiltrated through 
the above soil layer.  The geotextile filter fabric separating the two layers served as a 
barrier to prevent the fine soil particles from entering the EPS layer.  The intermediate 
scale model after installation of the ESP material, geotextile filter fabric, and silty sand 
material is shown in Figure 4.3 through Figure 4.5 and a cross-sectional view of the plots 
is shown in Figure 4.6.  The specifications for the SKAPS W200 Woven Geotextile 
Fabric are shown in Appendix C. 
 
 
Figure 4.3  Intermediate-Scale Model After Installation of EPS Material.
 
 
 
Figure 4.4  Intermediate-Scale Model After Installation of Geotextile Filter Fabric.
 66
 
LEFT 
PLOT
CENTER 
PLOT 
RIGHT 
PLOT 
 
Figure 4.5  Intermediate-Scale Model After Installation of Silty Sand Material. 
 
 
Figure 4.6  Cross-Section of Soil Plots. 
 67
4.2.2 Rainfall Simulator Design 
A new rainfall simulator was designed by the research team to provide uniform 
coverage over the three soil plot sections.  The simulator was made from ? in. schedule 
40 PVC pipe and consisted of six 1/8HH-3.6SQ Fulljet spray nozzles and a F-405 Series 
In-Line Flow meter.  These components were the same as those used in the previous 
simulator designed by Halverson (2006).  The six spray nozzles were configured in a 
rectangular grid and were spaced 32 in. apart in both directions providing each soil plot 
with two spray nozzles.  The spray pattern of these two nozzles provided nearly uniform 
coverage for their corresponding soil plots.  The configuration of the spray nozzles is 
shown in Figure 4.7.  One of the 1/8HH-3.6SQ Fulljet spray nozzles and the F-405 Series 
In-Line Flow meter are shown in Figure 4.8 and Figure 4.9 respectively and the 
specifications are included in Appendix D and E. 
 
 
Figure 4.7  Rainfall Simulator Configuration. 
 68
  
Figure 4.8  1/8HH-3.6SQ Fulljet Spray  
Nozzle. 
Figure 4.9  F-405 Series In-Line Flow 
Meter 
 
4.3 EXPERIMENTAL DESIGN 
Three different experimental scenarios were tested using a silty sand material on 
the intermediate-scale model developed at Auburn University.  These three scenarios 
consisted of a bare soil control and dry granular PAM applied at rates of 20 and 40 lb/ac.  
To yield reproducible results, each soil plot was prepared the same way and the same 
rainfall regimen was used throughout testing.  The details of the polymer selection, soil 
plot preparation, rainfall regimen, and data collection procedure used for the modeling 
effort will be discussed in the following sections.    
4.3.1 Polymer Selection  
Prior to using a PAM product, testing should be performed to determine which 
PAM product provides the best results for a particular type of soil.  A sample of the silty 
sand material being used for this research was sent to Applied Polymer Systems (APS) in 
Woodstock, GA.  APS recommended using the 705 Silt Stop powder applied at an 
 69
application rate of 35 to 45 lb/ac to provide the best results.  Therefore, the 705 Silt Stop 
powder was applied at the recommended rate (40 lb/ac) and half the recommended rate 
(20 lb/ac).  The 705 Silt Stop powder is shown in Figure 4.10 and the Material Safety 
Data Sheet (MSDS) for the product is attached in Appendix F. 
 
 
Figure 4.10  705 Silt Stop Powder. 
4.3.2 Soil Plot Preparation 
Prior to each test, the 6 in. deep soil plots shown in Figure 4.2 were loaded with 3 
in. of EPS material and covered with a SKAPS W200 Woven Geotextile Fabric.  The 
geotextile fabric was then fastened down and the silty sand material was loaded into the 
model in three 1 in. lifts.  Each lift was rolled 20 times for compaction using an 
aluminum weighted hand held roller that was fabricated at Auburn University.  The 
process of compaction by rolling each lift 20 times was determined by Halverson (2006).   
Halverson (2006) performed a standard proctor test on the silty sand material and the 
results showed that the optimum moisture content was 13.0% which corresponded to a 
 70
 71
compacted dry unit weight of 117.2 lb/ft
3
.  Additional testing by Halverson (2006) on this 
material showed that 20 passes over a 1 in. lift with the aluminum weighted hand held 
roller resulted in approximately 90% compaction at a moisture content of 7%.  Therefore, 
for our research, the water content of the material was raised to approximately 13% 
before loading it into the model and the material was compacted following the method 
used by Halverson (2006).   
On the day of testing, the soil plots were saturated and the 705 Silt Stop powder 
was applied.  Since the tests started from a saturated condition, surface runoff began 
immediately which increased the amount of erosion occurring on the model.   The 705 
Silt Stop powder was applied to the model using a salt shaker. The 40 lb/ac application 
rate translated to 6.4 grams of polymer powder per soil plot.   
4.3.3 Rainfall Regimen Used for Testing 
The simulated rainfall used in this research effort consisted of a combination of 
three successive high intensity, short duration storm events.  These high intensity, short 
duration storms were intended to simulate a worst case scenario situation and provide 
valuable information on the efficiency of the granular PAM as an erosion control 
technology.  The rainfall events used for the tests were approximately 5-yr, 15-minute 
storms for Mobile, AL with each having an intensity of 6 in/hr and duration of 15 
minutes.  There was a one hour break between each storm and the cumulative rainfall 
depth for the three successive storms was 4.5 in. over a 165 minute period.  A storm for 
Mobile, AL was used because it provided the most conservative 5-yr, 15-minute rainfall 
event for the State of Alabama.  
4.3.4 Data Collection Procedure 
During each model run, the total surface runoff and infiltration flow were collected 
in one minute intervals.  These samples were collected in clear, five quart buckets with 
volume markings up the sides.  The total runoff and infiltration volumes for each minute 
were recorded and a 50 mL grab sample was taken from each surface runoff collection 
bucket for turbidity analysis.  Prior to taking this turbidity sample, the surface runoff was 
stirred to represent the actual turbidity of the surface runoff when leaving the soil plots.  
Once the turbidity samples were collected, the surface runoff was poured into Hayward 
single-length filter bags with one micron pore sized pores.  The water was allowed to 
flow out of these bags and the bags were placed in the oven to obtain the dry weight of 
solids leaving the soil plots.  Each filter bag contained the transported sediment from five 
minutes of testing.  Therefore, there were a total of 27 bags used per experiment.  The 
buckets used for collection of the surface runoff and Hayward single-length filter bags 
are shown in Figure 4.11 and Figure 4.12 below. 
 
 
Figure 4.11  Collection Buckets for 
Surface Runoff. 
 
 
Figure 4.12  Hayward Single-Length 1 
Micron Filter Bags. 
 72
 73
 
After the tests, the 50 mL turbidity samples were taken to the lab and analyzed.  
Each of the samples was shaken up and a turbidity reading was taken using a Hach 
2100AN Tubidimeter to determine the turbidity of the surface runoff while leaving the 
soil plots.  This data was then plotted versus time to determine the effectiveness of PAM 
on reducing the turbidity of surface runoff.  Further analysis was done on samples from 
the first, fifth, tenth, and fifteenth minutes of each experiment.  These samples were 
shaken up, placed into the turbidity meter, and turbidity readings were recorded in one 
minute intervals for fifteen minutes.  These data sets showed turbidity reduction versus 
time and were used to determine the effect that PAM had on the settling time of the 
suspended solids in the surface runoff.  The procedures outlined in this section were 
repeated for every experimental scenario (bare soil control, 20 lb/ac PAM, 40 lb/ac PAM) 
and the results are discussed in the following section.   
4.4 RESULTS AND DISCUSSION 
 For each of the three tests, the cumulative volume (runoff plus infiltration) versus 
time, the cumulative surface runoff volume versus time, cumulative soil loss versus time, 
and turbidity of the surface runoff versus time were plotted to compare the results.  
Turbidity samples from the first, fifth, tenth, and fifteenth minutes were also analyzed to 
observe the effectiveness of the two application rates of PAM on the settling time of fine 
particles in the surface runoff.  These five data sets for each test will be discussed in 
detail in the following sections. 
4.4.1 Cumulative Volume versus Time 
 For each model run, the surface runoff and infiltration volumes were collected to 
determine if the three soil plot sections were receiving approximately the same amount of 
rainfall for each experimental scenario.  The cumulative volume (runoff plus infiltration) 
versus time was plotted for each soil plot section and the results are shown in Figure 4.13 
through Figure 4.15 below.  There was a one hour break in between each 15 minute rain 
event (Run 1- Run 3) but for illustrative purposes the data was plotted continuously.   
0
200
400
600
800
1000
1200
1400
1600
1800
0 5 10 15 20 25 30 35 40 45 50
Time (min)
Cumula
tive Vo
lume 
(
o
z)
Control
20 lb/ac
40 lb/ac
Run 1 Run 2 Run 3
Note: * Denotes a one hour break between runs
**
 
Figure 4.13  Cumulative Volume vs. Time: Left Soil Plot. 
 
 74
0
200
400
600
800
1000
1200
1400
1600
1800
0 5 10 15 20 25 30 35 40 45 50
Time (min)
Cumula
tive Vo
lume 
(
o
z)
Control
20 lb/ac
40 lb/ac
Run 1 Run 2 Run 3
Note: * Denotes a one hour break between runs
**
 
Figure 4.14  Cumulative Volume vs. Time: Center Soil Plot. 
 
0
200
400
600
800
1000
1200
1400
1600
1800
0 5 10 15 20 25 30 35 40 45 50
Time (min)
Cumula
tive Vo
lume 
(
o
z)
Control
20 lb/ac
40 lb/ac
Run 1 Run 2 Run 3
Note: * Denotes a one hour break between runs
**
 
Figure 4.15  Cumulative Volume vs. Time: Right Soil Plot. 
 
 75
 76
 As shown in Figure 4.13 through Figure 4.15, the cumulative volume (runoff plus 
infiltration) was approximately the same for each soil plot section (left, center, right) in 
each of the three experiments (control, 10 lb/ac PAM, 20 lb/ac PAM).  To take the 
comparison a step further, the cumulative volume of the three soil plots was compared to 
the theoretical rainfall volume over the three rain events to determine if mass balance was 
achieved.  A theoretical applied volume of 1,706 oz. per plot per event was used which 
correlated to the 6 in/hr, 15 minute storm event.  There were three rainfall events per 
experiment resulting in a total theoretical applied volume of 5,120 oz.  The difference 
between the measured cumulative volume (runoff plus infiltration) and theoretical 
applied volume for the three soil plot sections is shown in Table 4.1 through Table 4.3 
below. 
Table 4.1  Water Balance: Left Section. 
 
 
Experimental 
Scenario 
Cumulative 
Runoff  
Volume 
(oz.) 
Cumulative 
Infiltration 
Volume 
(oz.) 
Cumulative 
Total 
Volume 
(oz.) 
Theoretical  
Volume 
Applied 
(oz.) 
 
Percent  
Difference
(%) 
Control 4184 568 4752 5120 7.2 
20 lb/ac PAM 4172 742 4914 5120 4.0 
40 lb/ac PAM 4176 444 4620 5120 9.8 
 
 Table 4.2  Water Balance: Center Section. 
 
 
Experimental 
Scenario 
Cumulative 
Runoff  
Volume 
(oz.) 
Cumulative 
Infiltration 
Volume 
(oz.) 
Cumulative 
Total 
Volume 
(oz.) 
Theoretical  
Volume 
Applied 
(oz.) 
 
Percent  
Difference
(%) 
Control 4544 224 4768 5120 6.9 
20 lb/ac PAM 4396 672 5068 5120 1.0 
40 lb/ac PAM 4732 230 4962 5120 3.1 
 
 
 
 
 77
Table 4.3  Water Balance: Right Section. 
 
 
Experimental 
Scenario 
Cumulative 
Runoff  
Volume 
(oz.) 
Cumulative 
Infiltration 
Volume 
(oz.) 
Cumulative 
Total 
Volume 
(oz.) 
Theoretical  
Volume 
Applied 
(oz.) 
 
Percent  
Difference
(%) 
Control 4370 402 4772 5120 6.8 
20 lb/ac PAM 4381 574 4955 5120 3.2 
40 lb/ac PAM 4572 238 4810 5120 6.1 
 
As shown in Table 4.1 through Table 4.3, the three soil plot sections were close to 
attaining water balance for the three experimental scenarios (Control, 20 lb/ac PAM, 40 
lb/ac PAM).  The 40 lb/ac PAM experiment on the left soil plot had the largest percent 
difference at 9.8%, and the 20 lb/ac PAM experiment on the center soil plot had the 
smallest percent difference at 1%.  The difference in volume between the measured and 
theoretical volumes can probably be attributed to the fluctuation of the flow through the 
rainfall system due to pressure variances from the source and also to overspray lost off 
the model. 
4.4.2 Cumulative Surface Runoff Volume versus Time 
 Now that the three soil plot sections have been checked for water balance, the 
cumulative surface runoff versus time was plotted for each soil plot section (left, center, 
right) to determine whether or not the surface runoff was approximately the same for 
each experimental scenario (bare soil control, 20 lb/ac PAM, 40 lb/ac PAM).  This data is 
shown Figure 4.16 through Figure 4.18 below. There was a one hour break in between 
each 15 minute rain event (Run 1- Run 3) but for illustrative purposes the data was 
plotted continuously. 
0
200
400
600
800
1000
1200
1400
1600
1800
0 5 10 15 20 25 30 35 40 45 50
Time (min)
Cumu
lativ
e
 
Surf
a
ce Runoff
 Vo
lume (
o
z)
Control
20 lb/ac
40 lb/ac
Run 1 Run 2 Run 3
Note: * Denotes a one hour break between experiments
**
 
Figure 4.16  Cumulative Surface Runoff Volume vs. Time: Left Soil Plot. 
 
0
200
400
600
800
1000
1200
1400
1600
1800
0 5 10 15 20 25 30 35 40 45 50
Time (min)
Cumu
lativ
e
 
Surf
a
ce Runoff
 Vo
lume (
o
z)
Control
20 lb/ac
40 lb/ac
Run 1 Run 2 Run 3
Note: * Denotes a one hour break between experiments
**
 
Figure 4.17  Cumulative Surface Runoff Volume vs. Time: Center Soil Plot. 
 78
0
200
400
600
800
1000
1200
1400
1600
1800
0 5 10 15 20 25 30 35 40 45 50
Time (min)
Cumu
lativ
e
 
Surf
a
ce Runoff
 Vo
lume (
o
z)
Control
20 lb/ac
40 lb/ac
Run 1 Run 2 Run 3
Note: * Denotes a one hour break between experiments
**
 
Figure 4.18  Cumulative Surface Runoff Volume vs. Time: Right Soil Plot. 
 
 As shown in Figure 4.16 through Figure 4.18, each soil plot section (left, center, 
right) experienced approximately the same amount of surface runoff volume in each of 
the three experiments (control, 10 lb/ac PAM, 20 lb/ac PAM).  The largest difference was 
during the third rainfall event on the right soil plot.  There was a 6.8% difference between 
the control and the 40 lb/ac application rate of PAM.  When Figure 4.16 through Figure 
4.18 are compared to one another, it can also be concluded that the runoff volumes are 
approximately equal in the right, center, and left soil plot sections.  Therefore, the erosion 
results should not be biased because the surface runoff volume for the three experimental 
scenarios and the three soil plot sections were similar.  The summary statistics for the 
surface runoff of the three soil plots combined are shown in Table 4.4. 
 
 79
 80
Table 4.4  Surface Runoff Statistics: Three Soil Plots Combined. 
 
Rainfall 
Event 
 
Mean
(oz.) 
Standard 
Deviation 
(oz.) 
Run 1 1364 77.2 
Run 2 1441 56.5 
Run 3 1485 67.6 
 
4.4.3 Cumulative Soil Loss versus Time 
 The cumulative soil loss versus time for the three soil plot sections was plotted to 
determine the effectiveness of the two application rates (20 and 40 lb/ac) of PAM as an 
erosion control technology.  The results of the three individual soil plots along with the 
average of all three plots for the three consecutive rainfall events (Run 1 ? Run 3) are 
shown in Figure 4.19 through Figure 4.22 below.  There was a one hour break in between 
each 15 minute rain event but for illustrative purposes the data was plotted continuously.   
 
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20 25 30 35 40 45 50
Time (min)
Cumu
lative 
Soil Loss (g)
Control
20 lb/ac
40 lb/ac
Run 1 Run 2 Run 3
Note: * Denotes a one hour break between runs
**
 
Figure 4.19  Cumulative Soil Loss vs. Time: Left Soil Plot. 
 
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20 25 30 35 40 45 50
Time (min)
Cumu
lative 
Soil Loss (g)
Control
20 lb/ac
40 lb/ac
Run 1 Run 2 Run 3
Note: * Denotes a one hour break between runs
**
 
Figure 4.20  Cumulative Soil Loss vs. Time: Center Soil Plot. 
 81
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20 25 30 35 40 45 50
Time (min)
Cumu
lative 
Soil Loss (g)
Control
20 lb/ac
40 lb/ac
Run 1 Run 2 Run 3
Note: * Denotes a one hour break between runs
**
 
Figure 4.21  Cumulative Soil Loss vs. Time: Right Soil Plot. 
 
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20 25 30 35 40 45 50
Time (min)
Cumu
lative 
Soil Loss (g)
Control
20 lb/ac
40 lb/ac
Run 1 Run 2 Run 3
Note: * Denotes a one hour break between runs
**
 
Figure 4.22  Average Cumulative Soil Loss vs. Time for all Three Soil Plots 
 82
 83
 As shown in Figure 4.19 through Figure 4.22, the cumulative soil loss over time 
increased in each of the soil plots during the three rainfall events for all three modeling 
scenarios (bare soil control, 20 lb/ac PAM, 40 lb/ac PAM).  The PAM applications, 
however, did provide a soil loss reduction compared to the control in most cases.  The 40 
lb/ac PAM application reduced the average soil loss compared to the control for all three 
rainfall events and the 20 lb/ac PAM application provided a reduction in two of the three 
rain events.  The details of the model results for all three rainfall events are discussed 
below. 
During the first rainfall event (Run 1), PAM applied at 20 lb/ac reduced soil loss 
in the left and right soil plots by 17.8% and 36.4% respectively, but there was an increase 
of 180% for the center section.  PAM applied at 40 lb/ac reduced soil loss by 82.2% and 
62.2% for the left and right plots respectively, but soil loss increased by 21% for the 
center section.  Since the surface runoff for all three sections was approximately the 
same, the increase in soil loss in the center section could be attributed to the randomness 
associated with erosion.  On average, PAM applied at 20 lb/ac provided a 16% increase 
in soil loss while PAM applied at 40 lb/ac provided a reduction of 49% for the three soil 
plots during the first rainfall event.  Pictures of the three soil plots after the first rainfall 
event for the three testing scenarios (bare soil control, 20 lb/ac PAM, 40 lb/ac PAM) are 
shown in Figure 4.23 below. 
 
 
 
 
 
 
 
 
a.) Control 
 
b.) PAM Applied at 20 lb/ac c.) PAM Applied at 40 lb/ac 
 
Figure 4.23  Soil Plots After Run 1 
 
 The results from the second event (Run 2) were similar to the first.  However, the 
20 lb/ac application rate only provided a reduction in soil loss for the right section (54%) 
when compared to the control.  Soil loss increased for the other two sections (5% in the 
left and 278% in the center).  On average, PAM applied at 20 lb/ac reduced soil loss by 
1% for the second rainfall event.  PAM applied at 40 lb/ac, on the other hand, reduced 
soil loss in the left and right sections by 77% and 64% respectively while soil loss for the 
center section increased by 72%.  Once again, the increase in soil loss from the center 
section can probably be attributed to the randomness associated with erosion.  The 
average soil loss for the three sections during the second rainfall event decreased by 51% 
 84
for the 40 lb/ac application rate.  Pictures of the three soil plots after the second rainfall 
event (Run 2) for the three testing scenarios are shown in Figure 4.24. 
 
a.) Control 
 
b.) PAM Applied at 20 lb/ac c.) PAM Applied at 40 lb/ac 
 
Figure 4.24  Soil Plots After Run 2 
  
For the final rainfall event (Run 3), soil loss was reduced in all three sections for 
both the 20 and 40 lb/ac application rates when compared to the control.  PAM applied at 
20 lb/ac reduced soil loss for the left, center, and right sections by 15%, 22%, and 44% 
respectively.  PAM applied at 40 lb/ac reduced soil loss for the left, center, and right 
sections by 53%, 43%, and 72% respectively.  The average soil loss reduction for the 
third event was 30% for PAM applied at 20 lb/ac and 58% for PAM applied at 40 lb/ac.  
Pictures of the three soil plots after the third rainfall event for the three testing scenarios 
 85
are shown in Figure 4.25 and the reduction in soil loss compared to the control for the 20 
and 40 lb/ac application rates of PAM are summarized in Table 4.5 and Table 4.6. 
 
a.) Control 
 
b.) PAM Applied at 20 lb/ac c.) PAM Applied at 40 lb/ac 
 
Figure 4.25  Soil Plots After Run 3 
 
 
Table 4.5  Soil Loss Reduction for PAM Applied at 20 lb/ac. 
 
 Left Soil
Plot 
Center Soil
Plot 
Right Soil
Plot 
Average  
of Plots 
Run 1 18% -180% 36% -16% 
Run 2 -5% -278% 54% 1% 
Run 3 15% 22% 44% 30% 
 
Table 4.6  Soil Loss Reduction for PAM Applied at 40 lb/ac. 
 
 Left Soil
Plot 
Center Soil
Plot 
Right Soil
Plot 
Average  
of Plots 
Run 1 82% -20% 62% 49% 
Run 2 77% -72% 64% 51% 
Run 3 53% 43% 72% 58% 
 86
4.4.4 Turbidity Results 
Turbidity samples were collected every minute from the surface runoff of all three 
soil plots for the three rainfall events (Run 1 ? Run 3).  These samples were taken to the 
lab, agitated, and turbidity measurements were taken using a Hach 2100AN 
Turbidimeter.  The turbidity of the surface runoff versus time for the bare soil control and 
PAM applied at rates of 20 and 40 lb/ac for the three soil plot sections is shown in Figure 
4.26 through Figure 4.28 below.   The turbidity of all the samples collected during the 
control run was greater than 10,000 NTU.  However, a value of 10,000 NTU was used 
because the Hach 2100AN Turbidimeter would not read turbidities any higher 
0
2000
4000
6000
8000
10000
12000
0 5 10 15 20 25 30 35 40 45 50
Time (min)
Tu
rb
id
it
y (N
TU)
Control
20 lb/ac
40 lb/ac
Run 1 Run 2 Run 3
Note: * Denotes a one hour break between experiments
**
 
Figure 4.26  Turbidity of Surface Runoff vs. Time: Left Soil Plot. 
 
 87
0
2000
4000
6000
8000
10000
12000
0 5 10 15 20 25 30 35 40 45 50
Time (min)
Tu
rb
id
it
y (N
TU)
Control
20 lb/ac
40 lb/ac
Run 1 Run 2 Run 3
Note: * Denotes a one hour break between experiments
**
 
Figure 4.27  Turbidity of Surface Runoff vs. Time: Center Soil Plot. 
 
0
2000
4000
6000
8000
10000
12000
0 5 10 15 20 25 30 35 40 45 50
Time (min)
Tu
rb
id
it
y (N
TU)
Control
20 lb/ac
40 lb/ac
Run 1 Run 2 Run 3
Note: * Denotes a one hour break between experiments
**
 
Figure 4.28  Turbidity of Surface Runoff vs. Time: Right Soil Plot. 
 
 88
 89
 As shown in Figure 4.26 through Figure 4.28, the turbidity of the surface runoff 
was greatly reduced by the application of PAM.  PAM applied at 20 lb/ac reduced the 
average turbidity of the surface runoff for the three rainfall events by 95%, 65%, and 
46% respectively compared to the control.  The 40 lb/ac application of PAM performed 
even better and reduced the average turbidity of the surface runoff by 99%, 88%, and 
83% for the three rainfall events respectively.  These results show that PAM can be very 
effective at reducing the turbidity of surface runoff leaving construction sites. 
Further analysis was done on turbidity samples from the first, fifth, tenth, and 
fifteenth minutes of each rainfall event to determine if PAM applied directly to the soil 
surface promoted the flocculation of fine particles in the surface runoff and decreased 
their settling time.  To perform this analysis, each sample was agitated, placed in the 
Hach 2100AN Turbidimeter, and monitored for fifteen minutes.  An initial turbidity 
reading was taken and readings were taken in one minute intervals thereafter.  This data 
for the three rainfall events (Run 1 ? Run 3) is shown below.   
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
2 4 6 8 10121416
Time (min)
T
u
rbidity (NTU)
Control
20 lb/ac
40 lb/ac
 
Figure 4.29  Turbidity vs. Settling Time for Run 1 (1 min). 
 
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
2 4 6 8 10121416
Time (min)
T
u
rbidity (NTU)
Control
20 lb/ac
40 lb/ac
 
Figure 4.30  Turbidity vs. Settling Time for Run 1 (5 min). 
 90
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0 2 4 6 8 10 12 14 16
Time (min)
T
u
rbidity (NTU)
Control
20 lb/ac
40 lb/ac
 
Figure 4.31  Turbidity vs. Settling Time for Run 1 (10 min). 
 
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0 2 4 6 8 10 12 14 16
Time (min)
T
u
rbidity (NTU)
Control
20 lb/ac
40 lb/ac
 
Figure 4.32  Turbidity vs. Settling Time for Run 1 (15 min). 
 
 91
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0 2 4 6 8 10 12 14 16
Time (min)
T
u
rbidity (NTU)
Control
20 lb/ac
40 lb/ac
 
Figure 4.33  Turbidity vs. Settling Time for Run 2 (1 min). 
 
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0 2 4 6 8 10 12 14 16
Time (min)
T
u
rbidity (NTU)
Control
20 lb/ac
40 lb/ac
 
Figure 4.34  Turbidity vs. Settling Time for Run 2 (5 min). 
 
 92
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0 2 4 6 8 10 12 14 16
Time (min)
T
u
rbidity (NTU)
Control
20 lb/ac
40 lb/ac
 
Figure 4.35  Turbidity vs. Settling Time for Run 2 (10 min). 
 
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0 2 4 6 8 10 12 14 16
Time (min)
T
u
rbidity (NTU)
Control
20 lb/ac
40 lb/ac
 
Figure 4.36  Turbidity vs. Settling Time for Run 2 (15 min). 
 
 93
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0 2 4 6 8 10 12 14 16
Time (min)
T
u
rbidity (NTU)
Control
20 lb/ac
40 lb/ac
 
Figure 4.37  Turbidity vs. Settling Time for Run 3 (1 min). 
 
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0 2 4 6 8 10 12 14 16
Time (min)
T
u
rbidity (NTU)
Control
20 lb/ac
40 lb/ac
 
Figure 4.38  Turbidity vs. Settling Time for Run 3 (5 min). 
 
 94
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0 2 4 6 8 10 12 14 16
Time (min)
T
u
rbidity (NTU)
Control
20 lb/ac
40 lb/ac
 
Figure 4.39  Turbidity vs. Settling Time for Run 3 (10 min). 
 
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0 2 4 6 8 10 12 14 16
Time (min)
T
u
rbidity (NTU)
Control
20 lb/ac
40 lb/ac
 
Figure 4.40  Turbidity vs. Settling Time for Run 3 (15 min). 
 
 95
 96
 As shown in Figure 4.29 through Figure 4.40, the application of PAM 
dramatically reduced the settling time of the suspended particles in the surface runoff.  
The results for the 20 lb/ac PAM application show that during the first rainfall event (Run 
1) the initial turbidity was reduced on average of 96% compared to the control and was 
even as low as 180 NTU for the 10  minute sample.  The turbidity after 15 minutes of 
settling time dropped as low as 28 NTU for the same sample and the average turbidity 
after 15 minutes of settling time for Run 1 was 42 NTU.  The effect of PAM began to 
reduce a little bit during the second and third events, but the 20 lb/ac PAM application 
still provided a pretty good reduction compared to the control.  During the second and 
third events the average initial turbidity of the surface runoff was 4123 NTU and 4601 
NTU respectively and the average turbidity after 15 minutes of settling time was 204 
NTU and 262 NTU respectively.  The control for the second and third events had an 
average of 10,000 NTU for the initial turbidity and 377 NTU and 454 NTU respectively 
after 15 minutes of settling time.   
 The results from the 40 lb/ac PAM application were even better.  The initial 
turbidity was as low as 89 NTU for the 5 minute sample of Run 1 and the turbidity after 
15 minutes was as low as 23 for the 1 minute sample.  The average initial turbidity for the 
first event was 177 NTU and the average turbidity after 15 minutes of settling time was 
27 NTU.  These reductions continued into the second event.  The average initial turbidity 
for the second event was 847 NTU and the average turbidity after 15 minutes of settling 
time was 50 NTU.  The turbidity reductions for the third event, though a little worse than 
the first two, were still very good.  The average initial turbidity for the third event was 
1034 NTU and the average turbidity after 15 minutes of settling time was 81 NTU.   
 97
Table 4.7 through Table 4.8 show the average initial turbidity after 15 minutes of settling 
time for the three experimental scenarios (bare soil control, 20 lb/ac PAM, 40 lb/ac 
PAM).   
Table 4.7  Initial Turbidity. 
 
Experimental
Scenario 
Average 
Initial 
Turbidity
(Run 1) 
Average 
Initial 
Turbidity
(Run 2) 
Average 
Initial 
Turbidity 
(Run 3) 
Control 10000 10000 10000 
20 lb/ac PAM 423 4123 4601 
40 lb/ac PAM 177 847 1034 
 
Table 4.8  Turbidity After 15 Minutes of Settling Time. 
 
 
Experimental
Scenario 
Average 
Final 
Turbidity
(Run 1) 
Average 
Final 
Turbidity
(Run 2) 
Average 
Final 
Turbidity 
(Run 3) 
Control 315 377 454 
20 lb/ac PAM 42 204 262 
40 lb/ac PAM 27 50 81 
 
4.5  CONCLUSION 
Intermediate-scale experiments were performed to determine if dry granular PAM 
could be used as a potential erosion and sediment control technology in the highway 
construction industry.  The tests were performed on a physical model developed at 
Auburn University that consisted of three identical soil plot sections.  These sections 
were used to produce three replications of each experimental scenario.  A silty sand soil 
was used for the research and the experimental scenarios consisted of a bare soil control 
and PAM applied at rates of 20 and 40 lb/ac.  Three consecutive 6 in/hr, 15 minute 
storms were used for the experimental effort with a one hour break between each storm.  
 98
These high intensity, short duration storms, which were approximately 5-year, 15-minute 
rainfall events for the Mobile, AL area, were used to simulate a worst case scenario 
situation and provide valuable data on the longevity of granular PAM as an erosion 
control alternative.   
During each experimental run, the total surface runoff was collected in one 
minute intervals using clear five quart buckets.  A 50 mL turbidity sample was taken 
from each bucket and the buckets were then poured into Hayward single-length filter 
bags with a one micron pore size.  These bags were then placed in the oven to dry in 
order to determine the cumulative soil loss of each of the plots.  After testing was 
completed, the turbidity samples for every minute were taken to the lab, shook up, and a 
turbidity reading was recorded using a Hach 2100 AN Turbidimeter.  These readings 
were intended to represent the turbidity of the surface runoff when leaving the soil plots.  
Turbidity samples from the first, fifth, tenth, and fifteenth minutes of each rainfall event 
analyzed further.  These samples were shook up, placed in the turbidity meter, and 
readings were recorded in one minute intervals for fifteen minutes.  This data was used to 
determine the effect PAM had on the settling time of the fine particles in the surface 
runoff.  
The results from this research show that PAM applied at 20 lb/ac reduced the 
average soil loss for two of the three rainfall events and PAM applied at 40 lb/ac reduced 
the average soil loss for all three rainfall events when compared to the control.  This data 
shows that PAM applied in the dry granular form to a silty sand material could be a 
potential erosion control alternative if applied at the proper application rate.  From a 
turbidity reduction standpoint, the 20 lb/ac PAM reduced the average initial turbidity of 
 99
the three rainfall events by 95%, 65%, and 46% respectively and reduced the turbidity 
after 15 minutes of settling time by 87%,  46%, and 42% respectively compared to the 
control.  The 40 lb/ac PAM reduced the average initial turbidity for the three rainfall 
events by 99%, 88%, and 83% respectively and reduced the average turbidity after 15 
minutes of settling time by 91%, 87%, and 82% respectively compared to the control.  
The fact that the application of PAM greatly reduced not only the initial turbidity but the 
turbidity over settling time shows that PAM applied for surface stabilization can provide 
some sediment control benefits.  The turbidity of surface runoff can be greatly reduced if 
PAM applied for surface stabilization is used with other sediment control practices such 
as silt fence tieback systems and detention basins that impound stormwater runoff and 
provide adequate time for the suspended particles to settle out of suspension.   
 
 100
CHAPTER FIVE 
CONCLUSIONS AND RECOMMENDATIONS 
5  
5.1 INTRODUCTION 
This research focused on evaluating the use silt fence tieback (a.k.a. ?j-hook?) 
systems and dry granular PAM as erosion and sediment control technologies on highway 
construction sites.  The first portion of the research focused on silt fence tieback systems 
as a sediment control technology and the objectives were to: (1) develop a computational 
method to determine the storage capacity of a silt fence tieback system, (2) develop a 
Visual Basic (VBA) coded spreadsheet design tool for practitioners to use in the 
construction industry that predicts the amount of stormwater runoff generated from a user 
specified rainfall event and provides design guidance for a tieback configuration to 
accommodate the generated runoff, and (3) use the tool to design a tieback system on a 
local construction project and evaluate its performance over time during a case study. 
The second component of the research investigated the effectiveness of anionic 
polyacrylamide (PAM) as an erosion and sediment control technology.  The objectives of 
this component were to: (1) perform intermediate-scale experiments to determine the 
effectiveness of dry granular PAM applied to a typical 3H:1V slope for erosion control, 
(2) determine whether PAM, when used for erosion control, can also 
 101
provide sediment control benefits by decreasing the settling time of suspended solids in 
the surface runoff, and (3) provide recommendations for future erosion and/or sediment 
control testing using PAM.  The successes and failures of the work performed in these 
two areas and recommendations for future work will be discussed in the following 
sections.  
5.2 SILT FENCE TIEBACK SYSTEMS 
The first component of this research focused on silt fence tieback systems and was 
a continuation to the work performed by Halverson (2006).  A computational procedure 
was developed to determine the storage capacity of silt fence tieback systems and these 
procedures were used to create a Visual Basic (VBA) coded spreadsheet design tool to 
assist practitioners in the proper design of these systems.  This design tool was then used 
to design a tieback configuration to accommodate a 2 in. rainfall event on an ALDOT 
construction site in Auburn, AL.  The site consisted of an approximately 600 ft. 
symmetrical vertical curve section of road with a 3H:1V fill slope.  For comparative 
purposes, tiebacks were installed on half the site and a linear silt fence system was also 
installed on the rest.  The site was monitored over four storm events that totaled 4.4 in of 
rain.   
Throughout the four rainfall events, each of the tiebacks in the silt fence tieback 
system performed as expected by impounding stormwater runoff from their contributing 
drainage areas.  This allowed the suspended sediment in the surface runoff to settle out of 
suspension and be contained on site.  However, the fourth rainfall event had a cumulative 
depth of 2.5 in. which exceeded the design capacity of the system.  During this event, two 
 102
of the tiebacks were overtopped with water and nearly failed structurally from the 
excessive force associated with the large amount of impounded stormwater runoff.  These 
two tiebacks, though, still effectively contained sediment during the heavy rainfall event 
and the tieback system experienced no erosion along the toe of the fence in any of the 
four rainfall events.  To prevent structural failures from occurring in the future, additional 
steel support posts were installed at the locations where overtopping was experienced.  
The linear system, throughout the four rainfall events, performed much differently.  
It experienced heavy sedimentation at the downslope end of the fence and erosion along 
the toe of the fence in multiple upslope areas.  This erosion was caused by stormwater 
runoff accumulating along the fence and flowing in the downslope direction.  Also, a 
scour hole developed at the lowest point in the system during the fourth event. This was 
probably due to the high velocity concentrated flow that occurred along the fence during 
the storm.  When the high velocity flow reached the lowest point in the system, the shear 
stress caused by flow exceeded that of the underlying soil which resulted in a scouring 
effect.  This scour hole, if not fixed, will become deeper with every rainfall event and 
allow sediment to escape under the fence and leave the project.   
The results from this research show that silt fence tieback systems, if designed and 
installed correctly, are much more effective at distributing the total sediment load and 
containing sediment than linear systems.  In this study, the linear system experienced 
heavy sedimentation at a single location and erosion along the toe of the fence.  These are 
two of the five most prevalent failure modes of silt fence systems outlined by Halverson 
(2006).  The tieback system, on the other hand, did not experience any of these failure 
modes.  Therefore, the tieback configurations performed more effectively than the linear 
 103
system during the four rainfall events.  For future installations of tieback systems, the 
research team suggests that a spacing of no more than 5 ft. should be used for the support 
posts for the last 10 ft. of fence before the fence is tied into the fill slope.  This will 
provide extra structural support for the tieback system if an there is an overtopping 
condition. 
5.3 INTERMEDIATE-SCALE EROSION CONTROL EXPERIMENTS USING 
PAM 
The second portion of this research focused on the effectiveness of dry granular 
PAM as an erosion control technology.  Testing was performed on an intermediate-scale 
physical model developed at Auburn University and three experimental scenarios (bare 
soil control, 20 lb/ac PAM, 40 lb/ac PAM) were investigated.  Three consecutive 6 in/hr, 
15 minute storm events were used for the experiments with a one hour break between 
each storm.  The 20 lb/ac application rate of PAM reduced the average soil loss for the 
second and third rainfall events by 1% and 30 % respectively, and PAM applied at 40 
lb/ac reduced the average soil loss for all three rainfall events by 49%, 51%, and 58% 
respectively.  The average turbidity of the surface runoff was also reduced by the 20 and 
40 lb/ac application rates of PAM.  PAM applied at 20 lb/ac reduced the average initial 
turbidity for the three rainfall events by 95%, 65%, and 46% respectively and the 40 lb/ac 
application rate reduced the average initial turbidity by 99%, 88%, and 83% respectively.  
Additional analysis was done to determine if PAM, when used as an erosion control 
technology, provided sediment control benefits by reducing the settling time of 
suspended sediment in the surface runoff.  This data showed that PAM applied at 20 lb/ac 
 104
reduced the average turbidity after 15 minutes of settling time by 87%, 46%, and 42% for 
the three rainfall events respectively.  The 40 lb/ac application rate provided even better 
results by reducing the average turbidity after 15 minutes of settling time by 91%, 87%, 
and 82% for the three rainfall events respectively. 
The results from this research suggest that dry granular PAM could serve as a 
potential erosion control technology if applied at the right application rate.  Prior to using 
PAM, soil specific testing should be done to determine exactly which PAM product to 
use and what the proper application rate should be.  Applied Polymer Systems 
recommended using the Silt Stop 705 powder for this research at an application rate of 
between 35 and 45 lb/ac.  Therefore, a rate of 40 lb/ac was used and provided a reduction 
in the average soil loss and turbidity for all three rainfall events.  Half of the 
recommended rate was also used (20 lb/ac) and still provided an reduction in average soil 
loss and turbidity but the results were not nearly as good as the 40 lb/ac application rate.  
From a sediment control standpoint, PAM applied as an erosion control BMP greatly 
decreases the settling time of suspended sediment in the surface runoff.  Therefore, the 
turbidity of runoff leaving construction sites can be greatly reduced if PAM applied for 
surface stabilization is used with other sediment control practices such as silt fence 
tieback systems and detention basins that impound stormwater runoff and provide 
adequate time for the suspended particles to settle out of suspension.   
 
 105
5.4 RECOMMENDED FURTHER RESEARCH 
5.4.1 Silt Fence Tieback Systems 
The field study performed on the ALDOT construction site comparing silt fence 
tieback and linear systems established the fact that silt fence tieback systems, if designed 
and installed correctly, perform much more effectively than linear systems in containing 
sediment and reducing potential failure modes.  More research should be done comparing 
the two systems to further strengthen the case for using silt fence tieback systems and 
determine if silt fence tieback systems consistently perform better.  Other research in this 
area should address possible construction methodologies of tieback systems and 
determine which methodology provides the most structurally sound system and is still 
cost effective.  If these issues are addressed and the information is shared throughout the 
construction industry, structurally sound, cost effective silt fence tieback systems can be 
designed and sediment leaving construction sites can be greatly reduced.   
5.4.2 PAM as an Erosion Control Technology 
Further research needs to be conducted to determine the exact role of PAM as an 
erosion control BMP in the highway construction industry.  This study evaluated PAM 
applied in dry granular form without ground cover practices to a silty sand material.  
Future work should evaluate the effectiveness of dry granular PAM used with ground 
cover practices such as straw and erosion control blankets (ECBs).  This includes the so-
called ?soft armoring? technique included in the Polymer Enhanced Best Management 
Practice (PEBMP) Application Guide by Applied Polymer Systems, Inc., the University 
of Central Florida, and the Stormwater Management Academy.  Other research should 
 106
investigate the effectiveness of PAM applied in the liquid form both with and without 
ground cover and ground cover practices should also be evaluated by themselves.  This 
work should be done on both intermediate-scale physical models and field-scale plots to 
determine if there is a direct correlation between what works in the lab and what works in 
the field.  These experiments should also be performed on multiple soil types to establish 
a clear understanding of the interaction and effectiveness of PAM when applied to 
different materials.  Finally, a comprehensive guide should be written documenting all of 
these studies and provided to ALDOT to give them a good understanding of the 
advantages and disadvantages of using PAM on highway construction sites.   
 107
REFERENCES 
 
1. Alabama State.  Alabama Soil and Water Conservation Committee.  Alabama 
Handbook for Erosion Control, Sediment Control, and Stormwater Management on 
Construction Site and Urban Areas: Volume 1.  Montgomery: Alabama, 2003. 
 
2. Alabama State.  Alabama Soil and Water Conservation Committee.  Alabama 
Handbook for Erosion Control, Sediment Control, and Stormwater Management on 
Construction Site and Urban Areas: Volume 2.  Montgomery: Alabama, 2003. 
 
3. Applied Polymer Systems, Inc., University of Central Florida, Stormwater 
Management Academy (2006).  Polymer Enhanced Best Management Practice 
(PEBMP) Application Guide.   
 
4. Barrett, M.E., Kearney, J.E, McCoy, T.G, and J.F. Malina.  An Evaluation of the Use 
and Effectiveness of Temporary Sediment Controls.  Center for Research in Water 
Resources Technical Report 95-6, The University of Texas at Austin, Austin: Texas, 
1995. 
 
5. Bjorneberg, D. L., J. K. Aase, et al. (2000).  Controlling sprinkler irrigation runoff, 
erosion, and phosphorus loss with straw and polyacrylamide.  Transactions of the 
ASAE, 43(6): 1545-1551. 
 
6. Flanagan, D. C., K. Chaudhari, et al. (2002a).  Polyacrylamide soil amendment effects 
on runoff and sediment yield on steep slopes: Part I. Simulated rainfall conditions.  
Transactions of the ASAE, 45(5): 1327-1337. 
  
7. Flanagan, D. C., K. Chaudhari, et al. (2002b).  Polyacrylamide soil amendment effects 
on runoff and sediment yield on steep slopes: Part II. Natural rainfall conditions.  
Transactions of the ASAE, 45(5): 1339-1351. 
 
8. Flanagan, D. C., L. D. Norton, et al. (2003).  Using polyacrylamide to control erosion 
on agricultural and disturbed soils in rainfed areas.  Journal of Soil and Water 
Conservation, 58(5): 301-311. 
  
9. Flanagan, D. C., L. D. Norton, et al. (1997a).  Effect of water chemistry and soil 
amendments on a silt loam soil - Part 1: Infiltration and runoff.  Transactions of the 
ASAE, 40(6): 1549-1554. 
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10. Flanagan, D. C., L. D. Norton, et al. (1997b).  Effect of water chemistry and soil 
amendments on a silt loam soil - Part 2: Soil erosion.  Transactions of the ASAE, 
40(6): 1555-1561. 
 
11. Flanagan, D. C., L. D. Norton, et al. (1997b).  Effect of water chemistry and soil 
amendments on a silt loam soil - Part 2: Soil erosion.  Transactions of the ASAE, 
40(6): 1555-1561. 
 
12. Halverson, J.L. (2006).  Use of a Small-Scale Erosion Control Model in Determining 
the Design and Effectiveness of Silt Fence Tiebacks Along Highway Projects.  MS 
Thesis, Auburn University.   
 
13. Hayes, S. A., R. A. McLaughlin, et al. (2005).  Polyacrylamide use for erosion and 
turbidity control on construction sites.  Journal of Soil and Water Conservation, 
60(4): 193-199. 
  
14. Lentz, R. D., R. E. Sojka, et al. (2002).  Fate and efficacy of polyacrylamide applied 
in furrow irrigation: Full-advance and continuous treatments.  Journal of 
Environmental Quality, 31(2): 661-670. 
 
15. McLaughlin, R.A. (2006).  Soil Facts.  Using Polyacrylamide to Reduce Erosion on 
Construction Sites.  N.C. State University and N.C. A&T State University 
Cooperative Extension.   
  
16. McLaughlin, R. A. and T. T. Brown (2006).  Evaluation of erosion control products 
with and without added polyacrylamide.  Journal of the American Water Resources 
Association, 42(3): 675-684. 
 
17. Novotny, Vladimir.  Water Quality: Diffuse Pollution and Watershed Management.  
New York: John Wiley & Sons, Inc., 2003. 
  
18. Peterson, J. R., D. C. Flanagan, et al. (2002).  PAM application method and 
electrolyte source effects on plot-scale runoff and erosion.  Transactions of the 
ASAE,  45(6): 1859-1867. 
 
19. Roa-Espinosa, A., G.D. Bubuenzer, and E.S. Miyashita, 1999.  Sediment and Runoff 
Control on Construction Sites Using Four Application Methods of Polyacrylamide 
Mix.  American Society of Agricultural Engineers Annual Meeting Paper No. 99-
2013, ASAE, St. Joseph, Michigan. 
 
20. Robichaud, P.R., D.K. McCool, C.D. Pannkuk, R.E. Brown, and P.W. Mutch.  Trap 
Efficiency of Silt Fences Used in Hillslope Erosion Studies.  American Society of 
Agricultural Engineers, 2001, pp. 541-543.   
 
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21. Shainberg, I., D. N. Warrington, et al. (1990).  Water-Quality and Pam Interactions 
in Reducing Surface Sealing.  Soil Science 149(5): 301-307. 
 
22. Stevens, E., Barfield, B.J., Britton, S.L., and Hayes, J.S.  Filter Fence Design Aid for 
Sediment Control at Construction Sites.  United States Environmental Protection 
Agency (U.S. EPA).  EPA 600/R-04/185.  Office of Research and Development, 
Washington: D.C., 2004. 
 
23. United States Environmental Protection Agency (U.S. EPA).  Federal Water 
Pollution Control Act.  Office of Water, Washington: D.C., 2002. 
 
24. United States Environmental Protection Agency (U.S. EPA).  Storm Water Phase II 
Final Rule: An Overview.  EPA 833/F-00/001.  Office of Water, Washington: D.C., 
2000a. 
 
25. United States Environmental Protection Agency (U.S. EPA).  Storm Water Phase II 
Final Rule: Small Construction Program Overview.  EPA 833/F-00/001.  Office of 
Water, Washington: D.C., 2000b. 
 
26. United States Environmental Protection Agency (U.S. EPA).  What is Nonpoint 
Source (NPS) Pollution?  Questions and Answers.  EPA-841-F-94-005, 1994.   
 
27. Zech, W.C., Halverson, J.L., and Clement, T.P.  Evaluating the Effectiveness of 
Various Types of Silt Fence Installations to Control Sediment Discharge from 
Highway Construction Sites. Submitted for possible publication in ASCE Journal of 
Hydrologic Engineering, 2006. 
 
 
 
 
 
 
 
 
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APPENDICES
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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APPENDIX A 
CURVE NUMBERS FOR SCS METHOD 
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 113
 114
APPENDIX B 
SILT FENCE TIEBACK DESIGN TOOL 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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DESIGN PROCEDURE 
Step 1).  Enter the input parameters and execute the design tool by pressing Ctrl+z. 
To determine an adequate tieback configuration, follow Steps 2-6: 
Step 2).  Divide the total length of the road by the largest silt fence length given in the   
Silt Fence Storage Capacity Computation Results to determine the minimum 
number of tiebacks required.   
 
Step 3).  Multiply the minimum number of tiebacks required with the total storage 
volume associated with the largest silt fence length in the Silt Fence Storage 
Capacity Computation Results. 
 
Step 4).  Compare this storage capacity with the results from the Stormwater Runoff 
Volume Computation. 
 
Step 5).  If the Storage Capacity given by Step 3 is greater than the stormwater runoff 
volume, use the tieback spacing from Step 2. 
 
Step 6).  If not, repeat Steps 2-5 using the next largest tieback spacing given in the Silt 
Fence Storage Capacity Computation Results. 
 
 
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APPENDIX C 
SKAPS W200 WOVEN GEOTEXTILE FABRIC SPECIFICATION 
 118
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APPENDIX D 
1/8HH-3.6 SQ FULLJET NOZZLE SPECIFICATION 
 120
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APPENDIX E 
F-405 SERIES IN-LINE FLOWMETER SPECIFICATION 
 
 
 
 122
 
 
 
 
 
 
 
 
 
 
 
 
 123
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APPENDIX F 
MSDS FOR 705 SILT STOP POWDER 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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