Assessment of the Relative Hydrologic Effects of Land Use Change and Subsidence Using Distributed Modeling

The heavy rainfalls associated with the geographic location of Houston in the Gulf of Mexico, the mild slopes, and the clay or loam soil, render the city of Houston prone to flooding. Over the last few years, an increasing number of significant flooding events in the Houston metropolitan area resulted in major human and economic losses and created the need for further and more detailed analysis of the localized causes of flooding. Two are the major concerns related specifically to flooding in Houston: the rapid urban development of the last fifty years, expressed through major land use change and channel modifications, and the associated continuing subsidence. It is well documented in scientific literature that urbanization affects the drainage pathways of a watershed leading to faster responses to rainfall events and increased total runoff volumes and peak flows. Additional studies conducted in the growing Houston metropolitan area support the idea that land use change has a significant effect on the shape of the runoff hydrograph and can become a major cause of flooding. Furthermore, the increasing groundwater pumping rates necessary to support the municipal water demand of the growing urban areas have resulted to variable land subsidence, altering the drainage network by locally reducing or enhancing preexisting slope gradients. The current study focuses on Whiteoak watershed at Northwest Houston, TX. During the last thirty years, Whiteoak experienced both major land use changes and continuing subsidence. The first objective of the study is to set up a distributed hydrologic model representing the Whiteoak basin and calibrate it at different points (USGS gauges) along the watershed. The second objective of the study is to evaluate the hydrologic impact of land use change during the period 1978 through 2000. The final objective of the study is to assess whether the significant land subsidence of Northwest Houston affects considerably the response of Whiteoak bayou at Lakeview gauge, located close to the position of maximum total subsidence. The Lakeview gauge is situated in a populated area of upper Whiteoak where the bayou is currently capable of carrying approximately a 25-yr storm event before overtopping its banks.