Low-flow characteristics of streams in the St. Croix River basin, Wisconsin

Abstract

The purpose of this report is to describe low-flow characteristics of streams in the St. Croix River basin where streamflow data have been collected and to present equations for estimating low-flow characteristics at ungaged sites. Included are estimates of low-flow frequency and flow duration at 7 gaging stations, and low-flow frequency characteristics at 26 low-flow partialrecord stations and 75 miscellaneous sites. Four equations are provided to estimate low-flow characteristics at ungaged sites and at sites where one base-flow discharge measurement is available. The low-flow characteristics determined were the annual minimum 7-day mean flow below which the flow will fall on an average of once in 2 years (Q7 9 2) and once in 10 years (Q7 s io)« The equations were determined from multiple-regression analyses that related the low-flow characteristics at gaging stations and lowflow partial-record stations to basin characteristics. Drainage area (A) was the most significant characteristic in explaining the variations in low flow for ungaged sites. The equations and standard error of estimates (SE) for ungaged sites are: 2 = 3.75X102A1 * 3° SE 2 = 110 percent nn = 1.05x10 A * ' SE^ __ = 150 percent 10 7»io For sites where one base-flow measurement has been made drainage area (A) and base-flow index (Bf) were the most significant characteristics. The equations and standard error of estimate are: QT 2 = O.U92A1 Bf1 ' 01 SE 2 = 38 percent _ = 0.235A1 ' 28Bf1 ' 21 SEV nn = 52 percent