A method for estimating mean annual runoff of ungaged streams based on basin characteristics in Central and Eastern Montana

Equations using basin characteristics were developed for estimating mean annual runoff at ungaged streams in central and eastern Montana. The study area was divided into three regions and separate multiple-regression equations were developed for each region. Drainage area was determined to be the most significant basin characteristic in all three regions. The standard error of estimate was 31 percent in Region 1 based on data from 17 stations. The standard error of estimate ranged from 64 to 51 percent in Region 2 based on 27 stations and ranged from 103 to 37 percent in Region 3 based on 29 stations; the standard error decreased as more independent variables were added to the estimating equation. Data from stations with less than 10 years of record were extended based on correlation with stations having long-term record. Coefficients of determination (R^) and equivalent years of record were determined and used as a basis for adjusting the record.