MODELING BASIN DISCHARGE RESPONSE TO CHANGES IN IMPERVIOUS SURFACES USING GIS AND HISTORICAL DATA

Impervious surfaces are artificial structures such as roads, buildings, and parking lots that are mostly impenetrable by water. These landscapes promote precipitation runoff as opposed to infiltration, which can affect both surface water discharge and groundwater recharge. This study uses GIS data available for percent change in impervious surfaces from the National Land Cover Database and historical USGS stream discharge data to evaluate this relationship. Percent change impervious surface data is available for the years 2001-2006 and 2006-2011; therefore, discharge data available for the time period 1997-2011 from the USGS Water Resource website was determined. Seven watersheds in north Georgia, of basin areas between 30-40 square miles, were identified. These basins represent both urban and rural settings and exhibit differences in percent change impervious surfaces over the time period of interest. Impervious surface data was then clipped to each delineated watershed using ArcGIS 10.2. Percent change in discharge for each watershed was calculated for the time periods 1997-2001, 2001-2006, and lastly 2006-2011. The percent change in discharge was then compared with percent change in impervious surfaces for each basin for years ending 2006 and 2011. Ideally a correlation between these two factors would be evident. The approach used here demonstrates that the time scale selected is perhaps too short to account for long term differences in precipitation (drought conditions) affecting stream discharge. It is well known that increases in impervious surfaces will increase stream discharge. Using the GIS techniques applied in this study on longer term data sets may demonstrate this behavior.