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Tuesday, May 19 1:30 - 3 :00 PM Track 5 - Erosion II - Moderator: Vince DiCamillo A NEWl,Y DEVELOPED EROSION BASED DAM FAILURE MODEL Frank Lan, PhD" Steve Rogers, P,E, ,John Sikora, P,E. A new methodology for performing flood wave routing associated with an overtopping earthen dam failure was developed, The method includes a combination of a physically based erosional model for simulating the dam failure and the United States Geologic Survey (USGS) unsteady flow model FEQ for routing the flood wave downstream of the dam, The dam failure was modeled as a gradual process of soil erosion caused by an overtopping flood, encountered by resistance of the embankment which is a function of the geotechnical properties of the embankment. Thus, the breach size and time of breach development of the failure would be detennined by the hydraulic forces of the flow and the resistance of the embm1kment. The new methodology takes advantages of the USGS unsteady flow model FEQ' s ability to handle complicated channel cross section profiles and provide more stable solutions, compared with the National Weather Service (NWS) Dambreak model. It will lead to better estimation of the dam failure flood wave, flood inundation limits and better development of emergency planning by better defining the area to be inundated in the event of a dam failure, The new methodology was applied to simulate the failure of earthen dams under extreme stonn events in the Chicago area, and the results are compared with the results obtained by using the more traditional methods such as tile NWS Dambreak model. ASSUMPTIONS USED IN THE DEVELOPMENT OF VARIOUS SEDIMENT TRANSPORT MODELS Jeffrey King Sediment concentrations for water floods range from 0.4 to 20 percent by volume, Sediment transport models typically predict concentrations at the low end of this range in areas where, intuitively, one would expect higher concentrations, Assumptions made in the development of various sediment transport models are identified, Modification of assumptions which may cause appropriate increases in concentration are discussed. LOCAL SCOUR OR DEPOSITION AND SEDIMENT TRANSPORT MODELS Mike Conaboy Sediment transport programs that are most widely used are intended to analyze general aggradation and degradation trends in a stream and, generally, will not properly evaluate local scour or deposition, Adjustments to the elevation of a cross section are made as a function of the water depth or based on an average amount of deposition or erosion. These procedures do not consider spatially varied scour and deposition associated with differences in cross sectional geometry along an alluvial channel. The presence of ridges Or incised areas along the channel can affect the location and amount of sediment movement. This paper will explore situations in alluvial channels where direct application of sediment transport programs may not reveal potential problems associated with local scour or deposition.