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Title: EROSION OF EARTH SPILLWAYS

Author
item Temple, Darrel
item WIBOWO, JOHANNES - USACE
item NEILSEN, MITCHELL - KANSAS STATE UNIV

Submitted to: United States Society on Dams Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2003
Publication Date: 4/14/2003
Citation: TEMPLE, D.M., WIBOWO, J., NEILSEN, M. EROSION OF EARTH SPILLWAYS. 2003. CD-ROM. PROCEEDINGS OF 2003 USSD ANNUAL MEETING AND CONFERENCE. CHARLESTON, SC: U.S. SOCIETY OF DAMS.

Interpretive Summary: Vegetated earth spillways are used in conjunction with hydraulic structures such as earth dams to safely pass large infrequent flows. These spillways may experience erosion damage during operation, but are considered to have performed satisfactorily if the erosion does not threaten the integrity of the structure. The erosion processes associated with performance of these spillways are complex and the technology used for performance prediction continues to evolve. A simplified computational model for performance prediction was developed by USDA for design and analysis of vegetated earth spillways on NRCS-assisted flood control reservoirs. This model was incorporated into NRCS Water Resource Site Analysis software, Sites, and is experiencing widespread use. In a continuing effort to refine the technology and expand the range of application, this model has been extracted from the Sites software and placed in a more specialized Integrated Development Environment. This form of application provides more flexibility for users involved in research or detailed analysis with the need to evaluate the effects of model variations or complex conditions. Proper application of this model will allow design of safe spillways at minimum cost.

Technical Abstract: The Natural Resources Conservation Service (NRCS) Water Resources Site Analyses computer program, Sites, contains a vegetated earth spillway erosion prediction model. Since the beta release of Sites in 1996, the program has been successfully applied in the analysis of a number of existing spillways as well as in the design and re-design of NRCS flood retarding structures. Work has also continued on refinement and extension of the model's erosion prediction relations through the evaluation of field data from spillways representing a wider range of conditions than were available during the original model development. To assist in this refinement effort and to make the spillway erosion model more easily applied to a wide range of conditions, the model code has been extracted from the more general Sites program and modified to make application more flexible. Changes made to date include upgrading the code to take advantage of features of FORTRAN 90, increasing the number of hydrograph data points that may be used in computation, providing a utility to import hydrograph data from HEC models, and providing the user additional flexibility in defining the headcut advance threshold and rate parameters. This paper presents the general principles of the Sites spillway erosion model and the implications of these modifications as they relate to its application. Model assumptions, application limits, strengths, and weaknesses are discussed in the context of the modifications and the ongoing research efforts.