Physically Based Hydrological Modeling of the 2002 Floods in San Antonio, Texas

Abstract

The July 2002 floods in South Texas resulted from excessive precipitation caused by a slow moving tropical wave accompanied by an abundance of tropical moisture, which resulted in 12 deaths and nearly $1 billion in damage. South Central Texas is particularly vulnerable to floods because of: (1) its proximity to a moist air source (the Gulf of Mexico); (2) the Balcones Escarpment, which concentrates rainfall runoff; (3) a tendency for synoptic scale features to become cut off and stall over the area; and (4) decaying tropical cyclones stalling over the area. This paper examines the hydrology of the July 2002 floods in three urbanized watersheds in the city of San Antonio and Bexar County, Texas. The physically based, distributed parameter gridded surface subsurface hydrologic analysis hydrologic model was used to simulate the flood over the three watersheds. Various flood control features were included in the simulations. The hydrologic model, driven by the next generation radar multi-sensor precipitation estimator, was able to reasonably simulate runoff in the three watersheds. Differences in the responses of the three watersheds were highlighted with the role of flood-control hydraulic structures.