|dc.description.abstract||The population growth in Houston over the last 30 years has been one of the fastest in the nation. Several studies have linked urbanization with increased runoff volume and peak discharges. For the watershed of Sims Bayou in the city of Houston, which has flat slopes, low permeability soils, and an aged storm water system, an increase in stream flows can signify an increase in flooding risk for a large number of people. Although attempts at solutions have been made by the USACE and HCFCD, increasing development in the area may be hindering those efforts.
This research study analyzes the flows and urbanization in the watershed through time to detect any trends. Annual peak flows and average daily flow records for two gages within the Sims Bayou watershed were analyzed and normalized by precipitation depths to diminish the variability of the time series caused by precipitation changes. Yearly development maps were developed using GIS. A yearly percent watershed developed value was then used to compare with the trends in flow. Since a positive relationship was observed between flows and urbanization for the selected gages, HEC-HMS was used to simulate the effect of urbanization alone on the watershed. By altering development values to reflect a development percentage similar to that occurring in the watershed in 1980, 1990, and 2000, the amount of runoff from the watershed for a 1% exceedance probability storm for development levels of 1980 and 2000 were compared. Changing development levels from 1980 to 2000 produced a 5% change in discharge at the watershed outlet. Using the results from HEC-HMS, a HEC-RAS model was used to assess the impact of such changes on flooding risk for residents of the Sims Bayou watershed. Regulatory floodplains for development levels similar to those in the watershed for 1980, 1990, and 2000 were mapped and compared. The increase in floodplain area resulting from changing development levels was approximately 15%. Unless both low-impact development alternatives and policies are implemented, more development in the watershed could signify more flood losses in the future.||