A Multi-Attribute Utility Theory Analysis of Alternative Erosion Control Materials to Class 2 Riprap in Alabama

Abstract

Riprap is an extremely common material for construction projects and often assumed to be the most cost-effective option for channel armoring. However, a study done by Auburn University found that in the state of Alabama riprap’s unit cost can fluctuate drastically based on the location of a given project. In the northern regions of the state riprap’s unit cost can be as low as 73% of the state average, whereas in the south near Mobile the rate can be increased as much as 160% that of the state average. This research study aimed to facilitate a more cost-effective and efficient decision process for material selection for channel armoring by focusing on materials available in Alabama. Historic bid data and unit price trends of riprap were compared to those of alternatives such as tied concrete block mats, turf reinforcement mats, and cellular confinement systems to compare the construction costs of all materials. These were coupled with geographic price variations, such as shipping costs, the life expectancy, projected maintenance, and flow resistance for each product. It was found that for initial construction turf reinforcement mats were universally more cost-effective than riprap with tied concrete block mats and cellular confinement systems being comparable in price in southern regions. Furthermore, a multi-attribute utility theory (MAUT) analysis was conducted for six different aspects of the material analyzed. This analysis method was then used to create a spreadsheet-based design tool called Channel Armoring Material Selector, which could be used for future project planning. The results of this study could prompt the Alabama Department of Transportation to revisit their approved channel erosion prevention techniques to allow for more cost-effective practices. This could lead to increased competition in the bidding of projects for ALDOT and an overall cost savings to taxpayers if implemented.