The objective of this research was to perform a watershed analysis of the City of El Paso Extra Territorial Jurisdiction (ETJ) drainage basin to examine the hydrological properties of the drainage basin and analyze the effects of sediment deposition on natural arroyos and existing drainage structure performance.

Watershed models were run using HEC-HMS (Hydrologic Modeling System) to determine the peak storm water discharge and watershed hydrographs during 25 year, 50 year, and 100 year storms. The HEC-RAS (River Analysis System) hydraulic modeling software was used for open channel flow computations and generating sediment transport models at major concentration points. The HEC-RAS models were run under steady state and quasi-unsteady flow conditions with the sediment transport analysis to compare the hydraulic performance of the channels and structural components during the August 01, 2006 storm event.

The models indicated severe failure in the hydraulic structures due to excessive flows and the increase in water surface elevations caused by sediment deposition upstream of the drainage structures. Field observations of post flood conditions supported the results and the channel behavior in the hydraulic models. The results suggest that a hydraulic and sediment deposition analysis is possible with HEC models and necessary for drainage structure design within the ETJ watershed. It is recommended that sediment transport models be incorporated as part of design criteria and modifications to existing flow paths to prevent catastrophic failures of drainage structures in El Paso County, Texas.