2007 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) Large-scale physical models will be used to evaluate and develop key relationships related to earthen spillway and embankment erosion. Small-scale physical models will be used for erosion and water control structure studies. Data and relationships from physical models and from the literature will be used in the development of predictive tools of the embankment breach process. This will include determination of the extent of overtopping that may be sustained by a vegetated earth embankment without resulting in breach, and quantification of the processes associated with breach such that timing, rate, discharge, and geometry of breach may be predicted. Other ARS scientists and university professors will collaborate with the USDA-ARS-PSWCRL in carrying out research objectives. The results of 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 nations agricultural watershed flood control infrastructure. 4.Accomplishments Engineering guidance for RCC Spillway: A specific hydraulic model study and preliminary summary report for a proposed spillway for Renwick Dam in North Dakota, was completed. The model study determined viable design of spillway dimensions, and downstream stilling basin dimensions and stable sizing of rock rip-rap downstream. These studies were conducted using a 1:8 scale model and running tests in a large flume at the USDA-ARS-Hydraulic Engineering Research Unit in Stillwater, OK. This study will contribute significantly to the planned design of this specific project and to future applications of planned RCC spillways for rehabilitation applications. (NP201, Problem Area 4-Integrated Soil Erosion and Sedimentation Technologies, Product 5-Best Management Practices and design tools for in-field erosion controls, gully and ephemeral channel erosion prevention, riparian corridor stabilization, and sediment retention structures) Beta version of a limited overtopping model completed: The beta version of the computer engineering application tool WIDAM, as a cooperative effort between the Hydraulic Engineering Research Laboratory, Natural Resources Conservation Service, and Kansas State University, has been completed. The application software will allow users to evaluate overtopping limits of vegetated embankments without failing the vegetation. The software will also determine the amount of flow through the principal spillway(s), auxiliary spillway(s), and over the vegetated or rock rip-rap protected earthen embankment. This computer tool will be important in evaluating existing structures, with potential of reducing costs associated with rehabilitation. (NP201, Problem Area 4-Integrated Soil Erosion and Sedimentation Technologies, Product 3-Improve tools for evaluating the potential for earthen embankment breach due to erosion and deterioration due to wave action) Erosion assessment guidance for compacted soils: Engineers commonly test and provide guidance for specifying soil compaction for construction projects involving embankments (i.e., dams, and levees). Presently, engineering specifications for construction of embankments are based on a range of required compaction water content and density to assure adequate strength and permeability but not to assure adequate resistance to erosion due to water flow over or through the embankment. At the Hydraulic Engineering Research Laboratory, a series of tests were conducted in the laboratory using jet erosion test equipment to measure the change in erosion resistance of soil materials at different water contents and compaction energy. The results indicate that the type of soil (i.e., sand, silt, and clay), compaction water content, and compaction energy are all important in determining erosion resistance of a soil and can effect erosion resistance by more than 1000 times. This research is important for engineers when specifying compaction requirements for construction of earthen embankments and will have important implications in improving embankment and levee safety during flooding events. (NP201, Problem Area 4-Integrated Soil Erosion and Sedimentation Technologies, Product 3-Improve tools for evaluating the potential for earthen embankment breach due to erosion and deterioration due to wave action) 6.Technology Transfer Number of non-peer reviewed presentations and proceedings 10 Review Publications Hanson, G.J., Hunt, S. 2007. Lessons learned using laboratory jet test method to measure soil erodibility of compacted soils. Applied Engineering in Agriculture. 23(3):305-312.