Integration of a surcharged pipe model and an overland flow model for flood prediction in a highly urbanized area

Abstract

Two models were incorporated to evaluate the hydrologic and hydraulic behavior of the Harris Gully watershed in Houston, Texas. A HEC-1 model was created and calibrated to three historical storms for average errors of 6% in peak flow, 4% in volume and 0.9 hours in peak time. The StormCAD model was used to determine capacity of the storm sewer system experiencing surcharged conditions and backwater effects. These capacities were incorporated into the HEC-1 model as diversions from the computed total runoff. The resulting model predicts the volume and approximate location of overland flow that can flood the system for any rainfall event scenario. Relationships were explored among storm intensity, duration, tailwater elevation and the resulting overland flow volume. Results show that any tailwater elevation over 40 feet shuts down the drainage capacity of the storm sewers. Three detention pond alternatives are proposed and their impacts were evaluated for flood-relief potential.