Erosion and Sediment Control
Performance Characteristics of Straw Mulch Using Different Anchor Methods Under Rainfall Induced Erosion on 3:1 Slopes
Construction sites can undergo significant erosion from disturbed areas devoid of vegetation. This erosion is often due to raindrop impact and/or overland flow. As erosion occurs, sediment may be transported down gradient to areas of deposition. These deposition areas may be in the form of sediment controls onsite or waterbodies offsite. Offsite sedimentation results in one of the nation’s greatest pollutants that can harm native aquatic wildlife. To minimize this potential, erosion controls are used to provide source control for sediment by minimizing erosive forces. Erosion controls typically cover the ground, armoring the surface by blocking direct impact of raindrops and slowing overland flow. Erosion controls are typically in the form of different types of mulch or erosion control blankets. These controls are included as part of an erosion and sediment control plan that is developed to provide contractors with the necessary information needed adequately control sediment on construction sites. Therefore, it is important to understand how different products and practices can be used to adequately control erosion on construction sites.
Straw mulch is a common, readily available material used as an erosion control on construction sites. Straw mulch may be applied by hand or blown on. Straw mulch may also require anchoring to minimize washing or blowing. Typical anchoring methods include use of a tacking agent and mechanical crimping. Performance testing of straw mulch with and without anchoring was performed by researchers at the Auburn-University–Erosion and Sediment Control Test Facility for the Alabama Department of Transportation.
Standardized testing has commonly been used to evaluate different products available to the erosion and sediment control industry. This provides standardization for different testing labs to follow as well as the ability to evaluate and compare the performance results of different products and practices tested. The testing method used for this research followed the requirements described by ASTM D 6459 - Standard Test Method for Determination of Rolled Erosion Control Product (RECP) Performance in Protecting Hillslopes from Rainfall-Induced Erosion. Performance testing evaluated sediment loss and water quality results for each test. In addition to the standardized method, performance longevity was also included to compare to straw mulch with and without anchoring. Each mulching condition was then compared to testing results from the control condition with no erosion control to determine the performance improvement and C-factor. The test data collected from this research will provide the industry with more information that can be used to help verify or amend currently used C-factors for predicting erosion rates. It will also provide better understanding of these practices when tested under longevity conditions that are not currently prescribed by ASTM D 6459.