ANALYSIS OF LAND COVER CHANGES AND THEIR HYDROLOGIC IMPACTS FROM 1974 TO 1990 IN GREENVILLE COUNTY, SOUTH CAROLINA

Urban sprawl is caused by different kinds of land transformations over time, including forest to urban, and agriculture to urban land cover. These changes result in an increase in impervious surfaces, an increase in runoff produced, and increased flooding potential within the urban area. Any attempt to reduce the impacts of urbanization on the local hydrology would first require quantification of the changes in land cover. The main purpose of this research was to develop current and historic land cover data using Landsat satellite data. In this study, Landsat TM and MSS images from 1974, 1986, and 1990 were used to perform unsupervised classification to produce land cover data for Greenville County, SC. This data was then used in combination with soil data and long-term precipitation data to evaluate the hydrologic impacts using the Long Term Hydrologic Impact Assessment (L-THIA) model. L-THIA can predict average annual runoff and NPS pollution load.

Results from classification showed consistent misclassification in urban land cover categories for 1986 data and hence our comparisons were limited to 1974 and 1990 only. We focused our comparisons on four watersheds located within the county from near the core of the City to the fringes of the City: Mountain, Brushy, Rocky, and Gilder Creek watersheds. In 1974, Mountain Creek had the highest forest cover ( 63.2%) and Brushy Creek had the highest urban land cover (47%) whereas the same numbers in 1990 were 64.3 % and 52%. The largest transformation during this period took place on Grass and Pasture land cover, with 12 - 14 % reduction in the three watersheds, except for Mountain Creek where it was less than 2 % reduction, and in most cases Grass and Pasture areas were transformed to urban uses. Runoff results indicate that Mountain Creek saw the highest total volume increase (135% increase between 1974 and 1990) in runoff likely due to several new high density residential neighborhood developments during this period, whereas low density residential and commercial developments contributed to the highest increase in runoff in Rocky and Gilder Creek watersheds that are located along the fringes of Greenville City. Further analysis of NPS pollutant load should provide more insight into the nature of water quality impacts to be expected in these watersheds.