Location: Delta Water Management Research Unit
Project Number: 6252-13000-002-14
Start Date: Jul 21, 2014
End Date: Jul 20, 2015
Increasing demands on limited groundwater resources have created a growing need for the development of surface water resources for irrigation. On-farm irrigation reservoirs, along with tailwater recovery systems offer an alternative practice for reducing dependence on groundwater supplies. The irrigation reservoir levees are typically constructed from local soils that may be low in clay content, and may sustain rapid erosion from both wind-driven waves and surface runoff if not maintained or protected. In spite of the need to increase surface water use in order to protect groundwater, the susceptibility of the reservoir levees to erosion, and the high cost of levee protection, very little research have been aimed at quantifying erosion and solving these issues. A key challenge that has not been addressed is determining how wave energy and erosion of cohesive soils are related. Defining this relationship would provide a basis for determining levee protection cost, how much longer a protected levee should last, and would help to guide future efforts in designing cost-effective protection methodology. A series of laboratory experiments will be conducted in the wave tank facility at the USDA-ARS National Sedimentation Laboratory. A model earth levee with 3:1 slope will be constructed using a silty loam soil inside the wave tank. The erosion rate will be measured for range of waves of a varying wave heights and periods. The results of this study will provide a basis for future experiments of different levee compositions, slopes, etc. Wave growth is mainly related to the wind speed, reservoir depth and the fetch length. In a reservoir, as the fetch length along the dominant wind direction increases the wave energy and therefore wave impact on the levee will also increase. In order to provide a measure for reservoir susceptibility to erosion damage, a shape factor that relates the orientation and geometry of reservoirs as well as dominant wind direction will be developed. The effectiveness of the shape factor in determining levee impairment will be investigated through field studies, which will include visits to selected reservoirs and basic assessments of their condition. It is expected that this exercise will lead to reductions in levee erosion through improvements in reservoir design and placement. As part of this process, a basic set of observations will be established for future use in rapid qualitative evaluation of levee impairment. Specific tasks: 1. Perform levee erosion experiments in the wave flume at the National Sedimentation Laboratory and relate a range of wave energies to the erosion rate of earthen levees. 2. Develop a shape factor with the goal of relating orientation and aspect ratio of irrigation reservoir levees to their degree of impairment. 3. Establish a procedure for rapid evaluation of levee impairment, to be used in verifying the predictive capability of the shape factor approach. This will include a list of observations, such as digital photographs taken from specific locations, which should be made in the assessment.