Assessment of Slope and Mechanical Treatments for an Irrigation Reservoir Embankment

Author(s): Ozeren, Y.; Wren, D.

On-farm irrigation reservoirs are commonly used in the Mississippi River Valley alluvial floodplain to complement limited groundwater resources. The inner slopes of the earthen embankments of these reservoirs are subjected to continuous erosion due to wind-generated waves. Various methods were applied in the past to protect the levees but none of these methods were sustainable and cost effective. In order to compare their effectiveness against wave erosion, several treatment techniques were applied on the levees of an irrigation storage reservoir at 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, as well as 5 different mechanical treatments along the north and south embankments. In 2015 and 2017, USDA-ARS and The University of Mississippi carried out two comprehensive surveys along the embankments of the UAPB reservoir. The surveyed cross-sections were compared with the as-built cross-sections to quantify the loss of soil so that the effectiveness of the treatment methods could be evaluated. Almost all of the slope configurations significantly eroded over the past 10-years. In general, milder slopes performed better than the steeper slopes. Although having a berm did not reduce the total eroded volume significantly, in most cases it delayed the bank top retreat. For sections with identical slope configurations, the section with the longest maximum fetch, regardless of bearing, typically had the highest erosion and bank top retreat. The survey results showed that mechanical treatment methods were more resilient against wave action as compared to the slope treatment methods.

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