Historical Land-Cover Changes and Hydrogeomorphic Adjustment in a Small Georgia Watershed
This study utilizes hydrologic modeling (HEC-1) for discrete episodes of land use in a Georgia watershed to portray the hydrologic adjustments that occur during a period of intensive land clearing and subsequent revegetation. It then compares these hydrologic shifts to field-based geomorphic adjustments such as gullying and valley aggradation. The Turner Creek watershed, settled in the mid-1830s, experienced a period of rapid land clearing with intensive cotton production (∼90 years) and then an extended period of reforestation (∼70 years), which generated hydrologic and geomorphic adjustments. Deep canyon formation in the poorly consolidated Coastal Plain lithologies occurred rapidly (∼30 years), causing upwards of 50 m of dissection. Results indicate that a new hydrologic regime has been established relative to both the prehistorical period (ca. 1800) and the period of maximum land clearing (ca. 1880), and that this hydrologic stability was achieved relatively quickly. Some geomorphic adjustments have coincided with the temporal pattern of hydrologic shifts. Aggradation rates, as determined by dendrochronology, have been a little slower to adjust but indicate an overall attenuation since 1948. Current sedimentation, unlike previous periods, is now most likely linked to the magnitude of spring storms. On the other hand, valley-side gully formation and stabilization are strongly linked to the pattern of hydrologic adjustments, as controlled by land-use patterns. Thus, this research indicates that watershed recovery and stability may be achieved, but it may differ from predisturbance conditions, and that not all hydrogeomorphic components respond similarly.