Location: Hydraulic Engineering Research2010 Annual Report
1a. Objectives (from AD-416)
Improve methods of predicting earthen embankment erosion and failure, and develop generalized hydraulic guidelines and tools for roller compacted concrete spillways used to protect earthen structures from erosion and increase discharge capacity. Improving methods of predicting earthen embankment erosion and failure will include sub-objectives of quantification and erosion measurement of embankment materials, quantification of protective capabilities of vegetation, development of algorithms and computational models that can be used by the profession to predict earthen embankment erosion and failure causing downstream flooding. The development of generalized hydraulic guidelines and tools for roller compacted concrete spillways will include sub-objectives of development of preliminary guidelines for dimensioning converging sidewalls as well as understanding air entrainment, flow bulking and energy dissipation leading to generalized equations for dimensioning stepped spillways, downstream basins and rip-rap protection that will be used by the engineering profession to design spillways.
1b. Approach (from AD-416)
Small-scale erosion tests and large-scale physical models will be used to develop knowledge of erosion resistance of embankment materials and to develop key relationships related to earthen embankment erosion. Small-scale and large-scale physical models will also be used for water control studies. Data and relationships from physical models and case studies from the literature will be used in the development of predictive and design tools for embankment erosion and spillway design. This will include determination of allowable overtopping and erosion processes associated with overtopping and internal erosion. Other ARS, government, university, international scientists and consultants will collaborate with the USDA-ARS-HERU in carrying 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
Bench erodibility tests at a wide range of compaction effort and water contents have been analyzed and compared to large-scale erosion tests on headcut and embankment breach tests. A series of Jet erosion tests and Hole erosion tests were completed, comparing the two methods and observing the erodibility variation of various soil types. The tests were conducted and analyzed in collaboration with the United States Bureau of Reclamation (USBR), United States Army Corps of Engineers (USACE), and Electricity DeFrance (EDF). Evaluated and validated predictive rate process algorithms using laboratory results from physical models, flume tests, and case histories for homogenous earthen embankments. Model evaluation has been conducted in collaboration with an international team coordinated by the Canadian Electrical Association Technical Interest, Dam Safety Interest Group (CEATI-DSIG). This team has completed evaluating state-of-the-art embankment breach computational models including technology developed by the USDA-ARS-HERU as well as models developed in Canada and in the UK. The WinDAM (Windows Dam Analysis Modules) development continued with WinDAM B. A beta test version of WinDAM B was produced that is a process-based breach erosion prediction model for homogeneous earthen embankment breach to be used by the engineering profession. Work is being conducted on development of internal erosion process modeling for the purpose of developing an internal erosion module of WinDAM. A relationship for determining the air entrainment inception point in roller compacted concrete (RCC) stepped spillways was developed. This relationship was further enhanced by data obtained from literature, making the relationship applicable for stepped spillways flatter than 22 degrees and having a Froude surface roughness between one and 100. Additional tests for obtaining air entrainment inception point were conducted and completed in a large-scale outdoor generalized model of a RCC 3(H):1(V) spillway over a range of discharges and step heights. hese data are being analyzed and used to validate the newly developed air entrainment inception point relationship. Modifications were made to a large outdoor flume, so testing could commence to obtain flow depths, velocities, air concentrations, and additional air entrainment inception point data over a range of discharges and step heights. Relationships for determining energy dissipation upstream and downstream of the inception point have been developed for stepped spillways having slopes of 14 degrees, and validated with a limited set of data from a 2.5(H):1(V) stepped spillway model study. The flow depth, velocities, and air concentrations will be analyzed, and energy dissipation will be determined for the large-scale 3(H):1(V) stepped spillway model to further validate the energy dissipation relationships developed.
1. Engineering guidance for Roller Compacted Concrete (RCC) spillways. Generalized physical model studies for flatter sloped RCC spillways were completed. These studies were conducted across multiple scales to investigate the effect step height has on air entrainment, energy dissipation, and flow bulking. An air entrainment inception point relationship for flatter sloped stepped spillways was developed, along with a generalized energy dissipation relationship. These relationships will provide the engineer with the tools necessary for designing training walls, specifying step heights and spillway basing lengths, and downstream protection requirements for RCC spillways for rehabilitation applications.
2. A beta version of a predictive overtopping breach erosion model completed. Present and future USDA Small Watershed Dams will require assessments to determine hazard classification, population at risk, and emergency action plans, and for prioritizing rehabilitation of aging infrastructure. A physically based dam embankment failure predictive model is essential in conducting in-depth assessments. A beta test version of the computer engineering application tool WinDAM B, as a cooperative effort between the USDA-ARS-Hydraulic Engineering Research Laboratory, Natural Resources Conservation Service, and Kansas State University, has been completed. The application software WINDAM allows engineers to evaluate embankment overtopping erosion, breach timing, breach location, breach failure, and flood discharge for flood overtopping of homogeneous earthen embankments. This computer tool will be important in evaluating existing structures, with potential for determining hazard classification, developing emergency action plans, and reducing costs associated with rehabilitation.Hunt, S., Kadavy, K.C. 2010. Energy dissipation on flat-sloped stepped spillways: Part 2. Downstream of the inception point. Transactions of the ASABE. 53(1):111-118.