Hydrologic analysis of urbanization and related parameters on flooding in the Brays Bayou watershed

Abstract

Although floods are natural phenomena, their impact is often aggravated, if not actually caused, by man's activities and occupation of floodplains. Urbanization of a floodplain drastically alters the flood characteristics of a stream by increasing the percentage of rainfall that becomes runoff and moving that runoff into drainage channels more rapidly. Flood flows are therefore quicker to peak and peak higher for the same amount of rainfall in an urban basin. One of the most rapidly urbanizing cities in the United States is the city of Houston, Texas; a city which also has one of the nation's most severe flood problems. In 1979 alone, Houston suffered $4 million in property damages as a direct result of flooding. Consequently, this research addresses the effects of urbanization on flooding by focusing on the Brays Bayou watershed, a basin which has experienced an enormous increase in development in the past ten years and is also one of the most frequently flooded areas in Houston. By modeling the watershed with the U.S. Army Corps of Engineers' HEC1-1 computer model, the following conclusions were reached: 1) Peak discharges are significantly increased as a result of urbanization; 2) The Brays Bayou channel can be expected to carry less than a 5-year design storm uniformly spread over the entire watershed; 3) The HEC-1 kinematic wave technique for modeling discharge is a valid simulation method when applied to a large urban watershed; the effects of storage due to backwater effects during large storms, however, must be simulated using a storage routing method in conjunction with the kinematic wave overland flow simulation.