Impact of Urbanization on Storm Response of White Rock Creek, Dallas, Texas.

This study documents hydrological changes resulting from urbanization of the upper sub-basin of White Rock Creek watershed in Collin and Dallas counties, Texas. The 66.4 square mile watershed was transformed from 87% rural in 1961 to 95% urban in 2002, following construction of the Dallas suburbs of Richardson, Addison, Plano and Frisco. The objective of the study was to investigate changes in the storm response of White Rock Creek in terms of peak storm flow, storm flow volume and lag time. The approach employed to compare pre- and post-urbanization hydrology was to develop average unit hydrographs for each time period and use them to generate the creek's storm flow response to a set of six hypothetical precipitation events. The results suggest that substantial hydrological changes have occurred. The average infiltration capacity of the watershed was reduced by about 60%, so that storm flow was generated at lower precipitation intensities in the post-urbanization period. Storm flow peak discharge and volume were more than doubled for a hypothetical 10-year precipitation event. Average lag time was about 45 minutes faster in the post-urbanization period. It was concluded that urbanization has significantly impacted the storm response of the creek and increased the potential for flooding. It is anticipated that similar hydrological changes will occur in other rapidly urbanizing watersheds in the Dallas-Fort Worth Metropolitan region.