EVALUATING THE CAPABILITY OF FLO-2D AND HEC-RAS-MDF TO MODEL THE ST. SOPHIA DEBRIS FLOW OF DEC. 25, 2003 AT THE ST. SOPHIA CHURCH CAMP IN SOUTHERN CALIFORNIA

On December 25, 2003, rainfall on a fire-impacted watershed in the San Bernardino Mts. resulted in a debris flow that impacted the St. Sophia Church Camp located at the base of the watershed resulting in the destruction of the camp and 14 fatalities. The event was modelled using FLO-2D and HEC-RAS-MDF and the results compared with both field-based data collected shortly after the event and in-event observational data. The FLO-2D model when applied to evaluate the scale and nature of the flow at the location of the Church Camp resulted in an estimated flow depth of 16-18 m and a flow velocity of 16-18 m/s. Based on comparison with the field data the FL-2D estimates of depths and velocities were clearly excessive. This result is likely due, in part, to the fluid density values associated with the St. Sophia debris flow exceeding the operational and design capacity of the FLO-2D model, this despite efforts to adjust for the higher flow densities. The HEC-RAS-MDF model produced depths in the 3.0-5.0 m range and a velocity of 3.6 m/s. In this instance the HEC-RAS-MDF model provided results that are more in keeping with the field-based and observational data of the flow depths and velocities based on both field mapping of the deposits and reports regarding observed velocities and flow characteristics.