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<br />VII. Application of the FLO-2D Mo,!!,al .. Case Studies <br /> <br />7.1 Application Procedure <br /> <br />FLO-2D has been utilized to predict flood hydraulics and to <br />delineate the flood hazard on a variety of engineering projects. <br />These include: <br /> <br />* Split flow around a hillside from overbank flooding of a <br />concrete lined channel; <br /> <br />* Analysis of flooding in an area of coalescing a.lluvial <br />fans; <br /> <br />* Design of a flood containment wall in an alluvial wash; <br /> <br />* Water flooding of an urban floodplain; <br /> <br />* A detailed study of channE~l overbank flow and channel <br />obstruction at the apex of an alluvial fan; <br /> <br />* Mudflow inundation of an urbanized alluvial fan. <br /> <br />Two applicatiom; are described in this section: 1) flood <br />delineation in an alluvial wash comparing the FLO-2D results with <br />those computed by the FEMA methodology; and 2) mudflo~l and water <br />flooding of an urbanized alluvial fan. A brief introduction is <br />presented to illustrate how to use FLO-2D to analyze various flood <br />hazard scenaricls on a.lluvial fans or urban floodplains. <br /> <br />Modeling alternate flood scenarios has been greatly <br />facilitated with AutoCAD-DCA software, and subsequent revisions to <br />the data file involving the size, number or location of the grid <br />elements is very fast and simple. 'rhe grid system may be redefined <br />or expanded to perform a detailed examination of flooding in a <br />particular area with smaller grid elemen~s, to encompass an area <br />previously omitted, or to investiga1::e, alternative flow hydrographs. <br />Multiple flood events, failure of a channel, or modifications of <br />the flow path by a proposed development may necessitate evaluation <br />of several flood scenarios. <br /> <br />A suggested approach to applying the model is as follows: <br /> <br />1. Establish the hydrology and various return period flood <br />hydrographs for the study area at the fan apex. If <br />necessary, use FLO-2D to simulate the development of the <br />flood hydrograph in the ups1:ream watershed and route it to <br />the fan apex or floodplain study area. Overland flow <br />roughness, rainfall and t,.he sediment concentration can be <br />varied to establish the discharge hydrograph from the <br />upstream watershed. ThE! FLO-2D upstream watershed <br />subroutine can be used in lieu of HEC-l or other <br />hydrologic models. <br /> <br />32 <br />