Melanie A. Burke, Wade L. Nutter
A study was undertaken to determine the effects of changes in stream channel morphology over time on the hydrologic processes and functioning of adjacent floodplain systems in the Oconee River Basin of the middle Georgia Piedmont. A variety of information was collected from thirty sites within the basin. Historic channel information was obtained from DOT bridge plans for selected sites. Modern channel morphology was determined through fieled surveys. Historic and modern bankfull discharges were calculated using Manning's equation. Bankfull recurrence intervals were determined using regional flood-frequency regression equations. From selected gaging stations annual peak-discharge data for various recurrence intervals and bankfull discharge data were used to determine bankfull recurrence intervals for various-sized streams. Results indicate that channel degradation has created channels with larger than historic bankfull capacities throughout the basin, and thus greater recurrence intervals for overbank flooding. Channel entrenchment was especially evident in upper reaches of the basin, while channel aggradation from the transport and deposition of upstream sediment was apparent in lower reaches. Bankfull return intervals were variable and generally high for tributary streams, and were less variable and lower for basins larger than 60 mi2. Implications are that floodplains associated with deeply incised channels do not receive overbank flooding as frequently as they once did and thus may have changed in regards to the nature of their hydrologic functioning.
