This report presents multiple-regression equations for estimating selected low-flow characteristics for most unregulated Ohio streams at sites where little or no discharge data are available. The equations relate combinations of drainage area, main-channel length, main-channel slope, average basin elevation, forested area, average annual precipitation, and an index of infiltration to low flows with durations of 7 and 30 days and average recurrence intervals of 2 and 10 years. Data from 132 long-term continuous-record gaging stations and partial-record sites in Ohio were used in the analyses.
Multiple-regression analyses were first performed by using data from all 132 sites in an attempt to develop equations that would be applicable statewide. Standard errors for the statewide equations were too high (111 to 189 percent) for them to be of practical use in estimating low streamflows.
Data for the state were then subdivided into five regions, and multiple-regression equations were developed for each region. Standard errors for four of the five regions improved, and raged from 43 to 106 percent. Standard errors for region 5 remained high (74 to 129 percent).
The multiple-regression equations presented in this report are not applicable to streams with significant low-flow regulation. The equations also are not applicable if (1) the site has been gaged and low-flow estimates have been developed from gaging-station records, (2) low flow can be estimated by the drainage-area transference method from data for a nearby gaged site, or (3) a sufficient number of partial-record measurements made at the site can be adquately correlated with concurrent base flows at a suitable index station.
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USGS Numbered Series
Multiple-regression equations for estimating low flows at ungaged stream sites in Ohio