Base flow of streams on Long Island, New York

On Long Island, base flow under nonurbanized conditions constitutes 90 to 95% of total stream discharge. Base-flow data from 19 continuously gaged streams are presented as monthly mean and annual mean discharge for water years 1960-75, which includes the 1962-66 drought. The data were derived by hydrograph-separation procedures that isolate mean daily base flow from mean daily discharge. A close empirical relationship between annual mean base flow and stream discharge at the 55-% duration point facilities estimation of average base flow and can be used in place of the more time-consuming hydrograph-separation technique. These data are needed in calibration of computer models that will be used to predict the effects of hydrologic stresses, such as sewering, on the Long Island ground-water system. (USGS)