Assessment of Levee Treatments for an Irrigation Reservoir in Arkansas

Abstract. On-farm irrigation reservoirs, together with tailwater recovery systems, are commonly used to store water in the Mississippi River Valley alluvial floodplain to supplement limited groundwater resources. The inner slopes of the earthen embankments that enclose these reservoirs are subjected to continuous erosion due to wind-generated waves. Various methods have been used to protect the embankments, but none of them have been shown to be both sustainable and cost-effective. In an effort to assess levee protection strategies, a range of treatment techniques, including levee configurations and surface treatments, were applied on the embankments of the University of Arkansas Pine Bluff (UAPB) Lonoke Demonstration Reservoir in 2007. The treatment techniques included 17 different slope configurations along the east and west embankments and five chemical and mechanical treatments along the north and south embankments. Embankment erosion was measured by comparing new surveys conducted in 2015 and 2017 with as-built information provided by the USDA Natural Resources Conservation Service (NRCS). The change in levee profile between the surveys and the as-built profiles was used to quantify the effectiveness of the treatment methods for protection against wave action. An artificial neural network (ANN) prediction model was developed to establish relationships between erosion parameters (eroded area and maximum retreat) and four independent variables (existence of berm, face slope, maximum effective fetch, and probability of wind speed). Data from 27 sections were used for training, and data from seven sections were used for testing. Almost all of the slope treatments were significantly eroded over the eight to ten years that elapsed between construction and the surveys. Although having a berm did not significantly reduce the total eroded volume, in most cases it delayed the bank retreat. For any two identical slope configurations, the one with the longest fetch typically had at least slightly higher erosion and retreat. In general, milder slopes performed better than steeper slopes. The survey results showed that geo-synthetic fabric, fly ash, and soil cement were more effective at reducing wave erosion than the other treatment methods. Keywords: Embankment erosion, Irrigation reservoir, Levee erosion, Wave erosion.