Parameter estimation for models of major rainfall induced floods in ungaged mountain basins of Colorado

Abstract

Study region: Rocky Mountains in Colorado including Front and San Juan ranges Study focus: Hydrologic modeling of ungaged mountain basins plays an important role in ensuring the safety of Colorado’s dams. Recent research has shown that infiltration-excess runoff, saturation-excess runoff, and subsurface stormflow can all contribute to streamflow generated by extreme rainfall in Colorado’s mountains, and the soil moisture accounting (SMA) method in HEC-HMS has been suggested as an appropriate approach to model these mechanisms. However, SMA requires estimation of parameters that have not been previously considered for large floods. The objective of this work is to develop methods to estimate SMA parameters for modeling the response to extreme rainfall in ungaged mountain basins of Colorado where calibration to observed discharges is not possible. New hydrological insights for the region: The proposed parameter estimation methods are tested for five basins in the Front Range and three basins in the San Juan Range that have streamflow data available for major flood events. For these historical events, the proposed uncalibrated models produce the same streamflow generation processes as calibrated models, and the predicted peak discharges from the uncalibrated models usually have 25% errors or smaller. For design storms, the peak discharges from the uncalibrated models can differ substantially from the peak discharges from calibrated models but are conservative relative to the envelope of observed peak discharges.

Keywords

• Colorado
• Mountains
• Hydrologic modeling
• Ungaged basins
• Parameter estimation
• Soil moisture accounting