Estimating monthly and annual streamflow statistics at ungaged sites in Idaho

Water-Resources Investigations Report 2001-4093

Prepared in cooperation with U.S. Department of Agriculture, Forest Service. -- An error on page 16, Table 4, equation for Q.20 for November, was corrected on June 26, 2003. On May 20, 2004, the drainage area (A) exponent for May at Q.50 in table 4 on page 16 was found to be in error and was changed to 1.02.



Updated monthly and annual streamflow information for the many ungaged streams throughout Idaho is needed to assist planners and managers with issues regarding fish and wildlife, water rights, and other land and water uses. To provide this information, the U.S. Geological Survey used a multiple-regression analysis to develop equations for estimating daily mean discharge exceeded 80, 50, and 20 percent of the time each month (80-, 50-, and 20-percent monthly exceedances) and mean annual discharge values at ungaged sites. The analysis produced estimating equations that relate specific streamflow statistics to basin characteristics. The standard errors of estimate, in log 10 , of the final estimating equations ranged from a minimum of 0.072 (+18.1 to -15.3 percent) to a maximum of 0.498 (+214.8 to -68.2 percent). The estimating equations might not yield reliable results for sites with basin characteristic values outside of the range of values used to develop the equations. The equations also are not applicable for regulated streams or those that exhibit significant gains and (or) losses as a result of spring flow, seepage through permeable streambeds, or irrigation diversions. The equations generally were more reliable for estimating the high monthly streamflow statistics (20-percent exceedances) than for estimating the low streamflow statistics (80-percent exceedances) in each region and all streamflow statistics in regions where annual streamflow is relatively low.

Study Area

Additional publication details

Publication type:
Publication Subtype:
USGS Numbered Series
Estimating monthly and annual streamflow statistics at ungaged sites in Idaho
Series title:
Water-Resources Investigations Report
Series number:
Year Published:
U.S. Geological Survey
Publisher location:
Reston, VA
Contributing office(s):
Idaho Water Science Center
iv, 36 p.
United States