Location: Hydraulic Engineering Research2013 Annual Report
1a. Objectives (from AD-416):
The long-term objective of this project is to develop stand-alone and integrated tools for engineers to evaluate allowable embankment overtopping; predict dam failure from overtopping and internal erosion for homogeneous and zoned embankments with simple and complex downstream embankment slope geometries; design alternative surface protection methods, including vegetation, riprap, and concrete blocks; and develop generalized design criteria for increased spillway capacity for small dams (i.e., less than 20 m high). Specifically, the objectives of this project are: Objective 1: Enhance the WinDAM model to predict erosion and breach of complex earthen embankment geometries and materials. Subobjective 1A: Quantify the impact of complex embankment geometries on erosion processes during overtopping, including: convergence zones at the intersection of the earthen embankment and valley walls, and embankment berms and toes. Subobjective 1B: Quantify the impact of changes in soil materials on erosion processes and rates of earthen embankment erosion and breach. Objective 2: Develop engineering tools for design of earthen embankment protection alternatives and increasing the discharge capacity of small dams. Subobjective 2A: Develop guidelines for dimensioning stilling basins and downstream channel protection for non-converging RCC stepped spillways constructed over existing earth dams. Subobjective 2B: Develop guidelines for dimensioning stilling basins and downstream channel protection for converging RCC stepped spillways constructed over existing earth dams.
1b. Approach (from AD-416):
Large-scale physical models will be used to develop knowledge on the protective capability of vegetation and/or riprap on embankment slopes with convergences and berms. Large and small-scale models will be used to develop knowledge of erosion resistance of zoned embankment materials and to develop key relationships related to earthen embankment erosion. Small-scale and large-scale physical models will also be used to develop knowledge on the impact of discharge, energy dissipation, flow depth, velocities, and downstream tailwater depth on stilling basin and downstream channel protection design for stepped spillways. Data and relationships developed from these physical models coupled with in-depth literature review will be used in the development of predictive and design tools for embankment erosion and spillway and stilling basin design. USDA-ARS HERU scientists will collaborate with other ARS, government, university, international scientists, and consultants to carry-out these objectives. The results from this research will be incorporated into evaluation tools, software, design criteria, and management practices that will allow the continued service and increased benefit of the nation's agricultural flood control infrastructure.
3. Progress Report:
ARS researchers at Stillwater, Oklahoma, along with cooperators from Kansas State University and the Natural Resources Conservation Service (NRCS) have for several years been developing the WinDAM (Windows Dam Analysis Modules) software for prediction of earthen embankment erosion failure. WinDAM is under continuous expansion and development as additional knowledge is gained from embankment breach erosion and failure process due to overtopping and internal erosion. WinDAM was updated to include algorithms to evaluate dam breach through internal erosion. WinDAM C, the pre-alpha version for internal erosion, is currently being tested, and a case history has been developed for evaluation. The next expansion of WinDAM is to include algorithms for predicting erosion processes for surface areas under extreme hydraulic attack (i.e., convergence zones and embankment toes and berms) during an overtopping event. Construction of outdoor physical models for conducting convergent and bench flow tests have been completed with one year of growing season on the Bermuda grass completed. The water delivery system to the convergent and bench flow testing facility is currently under construction. The outdoor facilities for conducting zoned embankment tests is ready for construction of the first test section. ARS scientists at Stillwater, Oklahoma, have for several years worked to develop design criteria for the cost-effective application of roller compacted concrete (RCC) stepped spillways used to increase spillway capacity and to provide overtopping protection of embankment dams. Data collection from a 2(H):1(V) stepped spillway has been completed and coupled with the data collected from 3(H):1(V) and 4(H):1(V) stepped spillways, making it one of the largest databases for stepped spillways. Data analysis and development of generalized air entrainment inception point, flow depth, air concentration, and energy dissipation relationships have been substantially met for 4(H):1(V), 3(H):1(V), and 2(H):1(V) stepped spillways. Limited data from literature is providing independent validation of these broader use of these relationships. Flow depth, velocities, and energy dissipation provide parameters for the design of stilling basins and riprap size for downstream channel protection for smooth chute spillways. Additional testing to evaluate the stilling basin and riprap size for downstream channel protection will allow verification of these relationships in the design for stepped spillways.
1. Incorporating algorithms into WinDAM to evaluate internal erosion of embankment dams. Dams have excellent safety records, but on occasion, dams do fail, placing life and property at risk downstream. ARS scientists at Stillwater, Oklahoma, cooperate with Kansas State University and the Natural Resources Conservation Service (NRCS) in the development of the WinDAM (Windows Dam Analysis Modules) software for prediction of earthen embankment erosion and failure. Algorithms were incorporated into WinDAM for the evaluation of internal erosion in embankment dams, and this pre-alpha version of WinDAM, known as WinDAM C, is being tested. Further enhancement of WinDAM is expected to evaluate dams prone to extreme hydraulic attack and erosion along convergence zones and embankment berms and toes during an overtopping event. Construction of physical models are nearing completion to evaluate these erosion prone areas. Advancements in prediction tools and increased knowledge of embankment breach erosion and failure processes due to overtopping and internal erosion can lead to improvements in 1) risk assessments, 2) ranking systems for prioritization of rehabilitation, 3) emergency action plans, 4) inundation maps, 5) flood warning systems, and 6) flood zoning.
2. Developing design guidelines for roller compacted concrete (RCC) spillways. Inadequate spillway capacity that can lead to increased flooding is a common deficiency for aging embankment dams. ARS researchers at Stillwater, Oklahoma, are developing generalized design criteria for RCC stepped spillways used for overtopping protection and increase spillway capacity. Enhanced and quantifiable design relationships (i.e., air entrainment inception point, flow depth, air concentrations, and energy dissipation) for stepped spillways have been developed. These relationships provide the necessary design tools for determining training wall height and stilling basin size for stepped spillways. An estimated 1100 embankment dams administered through the Natural Resources Conservation Service (NRCS) are expected to utilize this technology. Increased knowledge and improved prediction relationships of air entrainment properties within stepped spillways have great potential to extend the design life of thousands of embankments dams worldwide.
Hunt, S.L., Kadavy, K.C. 2012. Closure to "Inception point relationship for flat-sloped stepped spillways" by Sherry L. Hunt and Kem C. Kadavy. Journal of Hydraulic Engineering. 138(11):1004-1005.