Evaluation of Hydromulches as an Erosion Control Measure Using Intermediate-Scale Experiments
Type of Degreethesis
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Discharge of sediment-laden stormwater from active construction sites, such as highway construction projects, is a growing concern in the construction industry (Zech et al. 2007, 2008). The United States Environmental Protection Agency (USEPA) (2009c) has recently proposed a 280 nephelometric units (NTU) effluent limitation guideline (ELG) pertaining to construction site runoff, and the Alabama Department of Environmental Management (ADEM) requires construction site runoff in the state of Alabama to retain turbidity levels within 50 NTUs above background levels. The Alabama Department of Transportation (ALDOT) is one of many agencies in the construction industry striving to meet the federal and state government construction site ELGs; therefore there has been an increased interest in research efforts to test the performance of many different erosion control practices. One such erosion control practice, hydromulching, is the hydraulic application of mulches. Although mulching fill slopes for erosion control is not a new practice, new technologies and innovations in the hydromulch industry has allowed the development of superior erosion control products. The performance of perhaps the oldest and cheapest form of erosion control, conventional straw mulch, has been tested and reported by many researchers to be an effective erosion control measure. However, with advancing technologies and a rise in concern for nonpoint source (NPS) pollution flowing from construction sites into our streams, rivers, and lakes, the research of new and improved practices that reduce both erosion and sedimentation is needed. The purpose of this research effort was to test the intermediate-scale performance of four hydromulches: (1) Excel® Fibermulch II, (2) GeoSkin®, (3) HydraCX2®, and (4) HydroStraw® BFM and compare them to the performance of two conventional straw practices, crimped or tackified, and a bare soil control. The first phase of this research focused on researching and developing a method to accurately, uniformly, and efficiently apply hydromulch treatments to compacted and scoured 3H:1V fill slopes that mimic conditions similar to a highway embankment. The goal was to consistently achieve manufacturer specified application rates through the use of scientific methods. Ultimately, a method was developed enabling researchers to determine application rates per spray by a hydroseeder through confirmation of collected wet and dry mulch ratios. The second phase of this research focused on testing the performance of the four hydromulch treatments, the two conventional straw treatments, normalized to a bare soil condition, using 2 ft (0.6 m) wide by 4 ft (1.2 m) long test plots. Each treatment was subject to simulated rainfall, which was divided into four 15 minute rainfall events with 15 minute breaks in between, producing a total cumulative rainfall of 4.4 inches, representative of a 2-year, 24 hour storm event. To determine the overall performance of each treatment, initial turbidities, turbidity over time, and soil loss measurements were consistently collected from plot runoff. Large amounts of collected data enabled researchers to effectively determine the performance of each practice tested. According to experimental results from this research effort, HydroStraw® BFM has the potential to meet ADEM ELGs of 50 NTUs,with an approximate 100% average erosion reduction and 99% average sediment reduction when normalized to the bare soil (control) condition. Straw, tackified and HydraCX2(R) were capable of meeting the USEPA‘s 280 NTU ELG, and on average reduced erosion by approximately 98% and 99% respectively. Overall, the results showed that all six practices tested were successful in controlling erosion. However, it is recommended to use additives such as polyacrylamide (PAM) in conjunction with the six tested practices to promote deposition and further reduce turbidity levels of construction site discharge. The results discussed in this research are qualified by several factors such as scale, slope, soil type, soil compaction, rainfall simulation, and rainfall intensity; therefore the potential for biased conclusions and recommendations must be acknowledged and may not be representative of field-scale performance.
- Wesley Thurman Wilson_MS Thesis_Civil Engineering_PDF.pdf