Impacts of Urban Development on Reservoir Stage Frequency Relationships

The U.S. Army Corps of Engineers (USACE) operates Addicks and Barker Reservoirs to reduce flooding along Buffalo Bayou through the City of Houston. Extensive urbanization occurring throughout the watershed and floodplain during the past 50 years includes commercial and residential development adjacent to reservoir lands upstream of the dams. Reservoir stage-frequency relationships provide basic information required in analyses of the upstream flooding potential. A methodology for determining reservoir stage frequency relationships was adopted that includes three phases: (1) adjusting historical sequences of daily stream inflows for the effects of urbanization, (2) simulating reservoir operations, (3) performing a frequency analysis of the resulting annual series of peak reservoir stage. The first phase is accomplished using a computer program called FlowAdj, that is based on the NRCS CN equation. FlowAdj was developed in conjunction with the study. The second and third stages are performed using the HEC-5 and HEC-FFA computer programs developed by the USACE Hydrologic Engineering Center.