Base Flow of 10 South-Shore Streams, Long Island, New York, 1976-85, and theEffects of Urbanization on Base Flow and Flow Duration

摘要

The report quantifies the annual base flow of all 10 continuously gaged streamson the south shore of Long Island for each year from 1976 through 1985. Three graphical methods of streamflow analysis--hydrograph separation, double-mass-curve analysis, and flow-duration-curve analysis--are used to compare current flows with those before urbanization and to illustrate the nature and magnitude of streamflow changes that have occurred since the 1940's. Three 5-year time periods were chosen for comparison of base-flow and flow-duration data. The first period, 1948-52 (index period), represents hydrologic conditions in the drainage basins before extensive urban development; the second, 1971-75, represents the streams' response from 1948-52 to 1972-75 (23 years) to changes caused by urbanization; and the last represents the period of further adjustment of streamflow to changing hydrologic conditions from 1971-75 to 1981-85 (10 years).