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<br />I. INTRODUCTION <br />1.1 Purpose of Study <br />The Federal Emergency Management Agency (FEMA) contracted Simons, L i & <br />Associates, Inc. (SLA) to perform a Flood Insurance Study (FIS) of Cornet Creek <br />for the town of Telluride, Colorado. The location of the study area is shown <br />in Figure 1.1. Flood hazards associated with the alluvial fan formed by the <br />creek on which the town is located were specified for detailed study. <br />Historically, major flooding in the town has been associated with mud floods and <br />mud flows from Cornet Creek. <br />The fluid properties of mud flows aY'e highly variable and accurate <br />prediction of flow behavior is difficult. Mud flows are characterized by <br />transient phenomena such as surging and channe,'1 avulsion. Mud flows will often <br />abandon existing channels and create new flow paths across an a'lluvial fan. The <br />most practical approach to del ineating th" flood hazard on an alluvial fan, <br />therefore, is to determine the potential range of flood properties, such as <br />discharge, velocity, depth, and area of i nundat i on. By varyi ng roughnes s <br />coefficients, sediment concentration, and assumed flood scenarios, the worst- <br />case hazards can be delineated for precipitation/runoff conditions of specific <br />return period. <br />Flood-hazard deli neat i on for water floods, mud floods, and mud fl ows was <br />accomplished in this study through the application of a two-dimensional (2-D) <br />fI ood-rout i ng computer model with the capabi"1 i ty of rout i ng hyperconcentrated <br />sed i ment flows. The model ut i 1 i zed (MUDFLOW) was recent"ly developed by Dr, J. <br />S, O'Brien. General discussion of the model is presented in this report. A <br />detailed technical description of the model is provided in a separate report <br />(O'Brien and SLA, 1989). The model was approved for use in this study by the <br />FEMA Project Officer (personal communication, January 1989). <br /> <br />1.2 Scope of Work <br />The scope of work required the delineation of flood-hazard areas for <br />10-, 50-, 100-, and SOO-year return period ~Iater floods and mud flows along <br />Cornet Creek withi n the town of Tell uri de, Colorado. Thi s was accompli shed with <br />a work plan that included the following tasks: <br /> <br />1.1 <br />