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II. BACKGROUND The first attempt to simulate flow hydraulics on alluvial fans with the computer was developed by DeLeon and Jeppson (1982). Laminar, steady state, water flows were modeled one-dimensionally with enhanced flow friction factors. In 1985, Schamber and MacArthur developed a one-dimensional finite element modeling of mudflows. 0 I Brien (1986) designed ,'lone-dimensional mudflow model for watershed channels employing Bill1gham stresses for nonNewtonian fluids. Two-dimensional simulations of flows on alluvial fans began with Takahashi and Tsuj imoto in 1985. They proposed a finite difference model for debris flows based on a dilatant fluid model coupled with Coulomb flow resistanCE!. The dilatant fluid model was derived from Bagnold's dispersivE! stress theory (1954) which describes the stress resulting from the collision of sediment particles. Takahashi and Nakagawa (1989) modified this finite difference model to include turbulemce theory. Mapping of debris flows were presented in which the shear stresses were defined in terms of equivalent Manning'S resis'tance formulas. This model was limited by dispersive shear stress co,efficients which have not been verified by laboratory or field tes:ts. A two-dimensional, finite element model for routing mudflows was created by MacArthur and SchambE,r in 1986. This model was only applicable to fans with a simplifil~d, uniform topography. The mudflow was assumed to have Bingham fluid behavior, but the yield stress term was not defined. Turbulent and dispersive stresses were neglected. In 1988, FEMA contracted Simons, Li I< Associates, Inc. (SLA) to conduct a Flood Insurance Study (FIS) of Cornet Creek for the town of Telluride, Colorado. Initially, a two-dimensional computer model developed by the Corps of Engineers (COE) Hydrologic Engineering Center in cooperation vdth the University of Utah was proposed for the hydraulic analysis of flows on the Cornet; Creek alluvial fan. This model was a ve:rsion of the model developed by MacArthur and Schamber (1986). The application of the model to the Cornet Creek alluvial fan was unsuccessful. In September, 1988, the development of a two-dimensional, routing model for mudflows was initiated. Existing two-dimensional flood routing models were researchl~d to discover if one might be suitable for modification to simulate mudflows. The model chosen was the Diffusive Hydrodynamic Meldel (DHM) designed by T. V. Hromadka II and C. C. Yen and published by the USGS (Hromadka and Yen, 1987). within a year, a new computer model, FLO-2D (originally named MUDFLOW), had been (Jreated. The Telluride-Cornet Creek flood hazard delineation study was completed with the FLO-2D model. The results were submitted tel FEMA for review. FEMA later contracted with Simons, Li and Assc,ciates to undertake additional analysis of the Cornet Creek mudflows using the FLO-2D model. 2