Effects of urbanization on flood characteristics in Nashville-Davidson County, Tennessee

Streamflow data from 14 basins in Davidson County, Tenn., were extended in time by use of a digital model of the hydrologic system. The basins ranged in size from 1.58 to 64.0 square miles and ranged in extent of manmade impervious cover from 3 to 37 percent. The flood-frequency characteristics were defined by weighting frequency curves based on simulated discharges with those based on observed discharges. The average record length of the three rain gages used in simulation was 72 years, and the average record length of observed discharges was 11 years. Discharges corresponding to 2-, 5-, 10-, 25-, 50-, 100-year floods from the modeled basins were compared with discharges from regional equations for estimating peak discharge rates from rural basins. Basin lag times of the urban basins were compared with those of nearby rural basins. The analyses indicated that in a fully-developed residential area, the flood peaks and the basin lag times will not be significantly different from those expected from an undeveloped area. Data were not sufficient to determine if an increase in flood peaks would occur from extremely small basins with extremely intensive development. (Woodard-USGS)