Hydrologic impacts of land-use changes in coastal plain watersheds

Conservation programs developed and implemented by the USDA have led to land-use changes of large areas throughout the U.S. These changes in land-use may lead to changes in evapotranspiration and infiltration and subsequently to dramatic differences in hydrologic response. The impact of recent land-use changes was evaluated using observed precipitation and streamflow data from the Little River watershed in south-central Georgia in the U.S. Land-use patterns within the watershed were examined through classification of satellite images collected from 1975 to 2003. While some changes in land-use were determined, analysis of the data indicated that the overall changes were less than the typical classification errors obtained. Based on the analysis of the satellite imagery, conservation practices implemented in the Little River watershed have not significantly altered total forest acreage. In addition, 34 years of hydrologic data collected from this watershed do not indicate any significant changes in hydrologic patterns. The long-term average ratio of annual flow to annual precipitation for the Little River watershed has remained stable at approximately 0.27. Year-to-year variation of the ratio varied from a high of 0.41 observed during a year with above-normal winter rainfall to 0.06 observed during a year with very low annual rainfall. When subwatersheds of the Little River were compared, significant differences in their responsiveness to rainfall were found. Linear regression between precipitation and streamflow produced regression coefficients between 0.62 and 0.90. These differences were attributed to differences in physical characteristics and land-use. Long-term data from the watersheds indicate that streamflow response is dominated by annual and seasonal precipitation characteristics.