Modeling of Storm-Water Response under Large Tailwater Conditions: Case Study for the Texas Medical Center

Intense rainfall over coastal areas characterized by significant urban development, predominantly clay soils, and flat slopes can cause significant flooding problems. Extreme floods in coastal areas occur when storm-water systems lose capacity due to high levels in receiving streams. The Texas Medical Center is located near downtown in Houston, Texas, and extensive flooding during Tropical Storm Allison in June of 2001 crippled many of the facilities with approximately $1.5 billion in damages. In order to better understand dynamic responses and to design abatements to the existing infrastructure, the performance of the storm-water pipe systems under extreme receiving water conditions in a highly urbanized area was quantified by using an integrated model. A hydrologic/hydraulic model was created based on the storm water management model with NEXRAD radar rainfall and hydrographs generated from Hydrologic Engineering Center’s hydrologic modeling system. The model was accurately calibrated against historic storm events. The simulated double-peaked hydrographs explained that the significant backwater effects in Harris Gully worsened the flooding situation within streets by limiting storm-water outflow and overland flow. The analysis evaluated the existing storm-water system to identify potential pathways for overland flow and pipe flow to the receiving bayou, and proposed mitigation alternatives by incorporating additional major sewers to bypass the main culverts in the Harris Gully area in order to provide significant flood relief.