Estimating average base flow at low-flow partial-record stations on the south shore of Long Island, New York

Base flows of the 29 major streams in southeast Nassau and southwest Suffolk Counties, New York, were statistically analyzed to discern the correlation among flows of adjacent streams. Concurrent base-flow data from a partial-record and a nearby continuous-record station were related; the data were from 1968-75, a period near hydrologic equilibrium on Long Island. The average base flow at each partial-record station was estimated from a regression equation and average measured base flow for the period at the continuous-record stations. Regression analyses are presented for the 20 streams with partial-record stations. Average base flow of the nine streams with a continuous record totaled 90 cu ft/sec; the predicted average base flow for the 20 streams with a partial record was 73 cu ft/sec (with a 95% confidence interval of 63 to 84 cu ft/sec.) Results indicate that this method provides reliable estimates of average low flow for streams such as those on Long Island, which consist mostly of base flow and are geomorphically similar. (USGS)