Comparison of Changes in Runoff and Channel Cross-sectional Area as a Consequence of Urbanization for Three Chattahoochee River Subbasins, Georgia, USA

Hydrologic analysis was performed for three similar-size Chattahoochee River, Georgia, subbasins for the period 1961–2005, each reflecting differing degrees of urbanization. Median yearly runoff volume was higher for the highly urbanized Peachtree Creek subbasin than for less urbanized Big Creek and nearly rural Snake Creek. A comparison of median direct runoff relative to median streamflow between 1961–1989 and 1990–2005 indicated 5.99, 11.65, and 2.77 percent increases for Peachtree, Big, and Snake Creeks, respectively. Basin outlet channel cross-sectional data obtained over a similar timeframe illustrate that while both Snake and Big Creeks showed evidence of increased channel area since the onset of escalating urbanization (roughly 1970), Peachtree Creek, the basin with the longest history of urbanization, has begun to exhibit a slight decrease in channel area. This suggests that, while the majority of channel adjustment for Peachtree Creek may have accompanied earlier phases of development, the channel may now have entered an aggradational phase.