Tropical Storm Allison, a 500-year storm event, dropped significant rainfall across Southeast Texas. The storm system passed across Harris County as many as three times in five days, dropping up to 36 inches of rainfall. Klotz Associates immediately offered its professionals’ extensive drainage and flood control expertise to the various city and county organizations that would be responsible for finding solutions to the flooding and its impacts.

Klotz Associates has prepared hydrologic models for four of the major watersheds, including Cypress Creek, Spring Creek, Willow Creek, and White Oak Bayou, using state-of-the-practice computer software for hydrologic, hydraulic, and floodplain mapping. The firm utilized GIS-based watershed evaluations to better understand the latest conditions. NEXRAD radar imaging was used to evaluate dynamics of the actual rainfall event compared to the large rainfall gauge network results. Klotz Associates used LIDAR as part of its team effort to update drainage areas and hydraulics of the watersheds, then compared the results to gauge stage data and surveyed elevations of flooded structures. The firm created new HEC-HMS models to provide updated hydrologic analyses. Klotz Associates worked with updated HEC-RAS models for routing reaches and for flow distribution. The firm’s effort is completed, and the work of the team involved will result in updated flood plain maps for area watersheds.