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<br />tit THE USE OF FLO-2D TO MODEL WATER AND MUD FLOW DOWN ALLUVIAL FANS <br /> <br />Bruce A. Curtis1, Ph.D., P.E. and Nick Adeh2, P.E. <br />1999 CASFM Conference, September 22-24, 1999 <br /> <br />ABSTRACT <br /> <br />e <br /> <br />Many mountain communities are located at the base of alluvial fans and are incurring <br />growth up the slopes of these fans. There are few methods that can estimate the depth of <br />flow that will occur on these slopes for a particular rain event, so planning, locating, and <br />designing flood control facilities is extremely difficult. Due to the non-cohesive nature of <br />the material on alluvial fans and the steepness of the fans, rain events can turn into <br />mudflow events, which will increase the damages caused by a rain event and increase the <br />cost of mitigation measures. <br /> <br />FLO-2D is a relatively new program whose abilities are especially pertinent to these <br />mountain communities. FLO-2D is a two-dimensional, finite difference flood routing model, <br />which can also model sediment transport and mudflow events. It was used to model rainfall <br />runoff from Aspen Mountain down the alluvial fan and through Aspen, Colorado and also <br />model a possible mudflow event through the City of Aspen. A FLO-2D model was also <br />generated to demonstrate the possible effect that a new development can have on a <br />mudflow event. <br /> <br />The results of these modeling efforts demonstrate that accounting for the entrainment and <br />conveyance of sediment in a given runoff event (a mudflow) can increase the water surface <br />elevation significantly. New development can increase the water surface elevation of a <br /> <br />I Project Manager, WRC Engineering, Inc., Denver, Colorado <br /> <br />. 2 City Engineer, City of Aspen, Aspen, Colorado <br />