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<br />EFFECTS OF URBANIZATION ON FLOODS IN THE <br />DALLAS, TEXAS, METROPOLITAN AREA <br /> <br />By <br /> <br />George R. Dempster, Jr. <br />U.S. Geological Survey <br /> <br />ABSTRACT <br /> <br />The effects of urbanization on flood characteristics of streams <br />in the Dallas metropolitan area were studied by use of a digital model <br />of the hydrologic system. The model was calibrated by using observed <br />rainfall and runoff data from 19 storms in six basins having various <br />degrees of urbanization. The calibrated models were used with a 57- <br />year rainfall record to simulate 57-year records of annual peak dis- <br />charges in 14 basins. The flood-frequency characteristics were de- <br />fined by fitting the simulated 57-year records to log-Pearson Type III <br />distributions. <br /> <br />Regional peak-discharge equations, which can be used to determine <br />the maximum rates of discharge that could be expected to be equaled or <br />exceeded on the average of once in 1.25, 2, 5, 10, 25, and 100 years, <br />were derived from multiple-regression analyses. The relationships <br />among flood frequency, drainage area, and a coefficient of impervious <br />area are given in a nomograph. <br /> <br />The analyses indicate that in a fully-developed residential area, <br />the flood peaks will be 1.2 to 1.4 times those from an undeveloped <br />area; and the annual direct runoff will be about double that from an <br />undeveloped area. Data were not sufficient to determine the increase <br />in runoff from a highly industrialized area where the effective imper- <br />viousness approaches 100 percent. <br /> <br />-1- <br />