Derivation of homogeneous streamflow records for the Green River basin, Kentucky

Four flood-control reservoirs, Green River Lake, Nolin River Lake, Barren River Lake, and Rough River Lake, were completed in the Green River basin of Kentucky between 1959 and 1969. A digital computer model of these reservoirs and the stream reaches from the reservoirs downstream to the Green River at Calhoun, Ky., was developed to simulate mean daily streamflows. Simulations of 1941 through 1971 water year streamflows were made for both the pre-reservoir and post-reservoir basin conditions, thus supplying homogeneous data sets for low-flow analyses of eight stream sites. The 7-day, 10-year recurrence interval, minimum discharges of the simulated regulated flows exceed those of the simulated natural flows by about 30 cubic feet per second for the Barren River at Bowling Green, Ky., and about 260 cubic feet per second for the Green River at Calhous, Ky. Analyses of the pre-reservoir simulations show that, for seven of the stream sites, the model yields streamflow which have annual minimum 7-day average discharges that are not significantly different, at the 95 percent significance level, from those of the observed flows. Results of the post-reservoir simulations show that actual reservoir operation was not closely matched by the model. Therefore, the low-flow characteristics of the simulated regulated streamflows are merely estimates of those that could be expected if the basin were regulated according to the modeled reservoir operating criteria. (USGS)