An Analysis of Historic Flows in the Satilla River Using Two Statistical Methods
As development proceeds in the Coastal Plain, increased interest has been directed toward the flow of fresh water into coastal ecosystems. As part of a larger effort investigating changes that may have taken place in three Georgia Estuaries, a historic analysis of freshwater flows into the estuary of the Satilla River was conducted. The annual mean flow on the Satilla River at Atkinson for the period of record (1931-1998) shows a slight trend upward (p= 0.1.) A further analysis of the historic flows on the Satilla River measured at the USGS station at Atkinson was performed using two different methods that used higher resolution datasets to identify more subtle changes in the hydrograph. The first analysis was performed using the Indicators of Hydrologic Alteration (IHA) trend-analysis method, developed by Richter, et al, 1996, for The Nature Conservancy. This method generates 34 metrics of alteration using daily-flow data, and significant changes were observed in maximum and minimum flows during the winter months. A second analysis was performed using a hydrologic yield calculation modeled after the method of Chagnon, et al, 1996, and Moglen and Beighley, submitted, have used to asses the impacts of urbanization of runoff characteristics for a basin. The hydrographic yield (a ratio of runoff to precipitation) after typical storm events was calculated for storms between 1948 and 1998. The ordered set of these values was then analyzed on a seasonal basis and, again, the most striking results were observed for winter storms. While the range of yield values for storms in spring, summer, and fall was reasonably consistent, there is a marked increase in the variability of yield values for winter storms. As hydrographic yield is strongly influenced by land use, this pattern suggests that seasonally changing land uses (or land uses in which the land cover changes on a seasonal basis) may significantly be affecting runoff patterns in the Satilla basin.