Annual Flow Statistics for Ungaged Streams in Idaho

Abstract

Annual streamflow records for 124 stream gages in and near Idaho are examined to determine four annual flow statistics: the mean; the standard deviation; the skew coefficient; and first‐order serial correlation coefficient. Using step‐wise regression analysis, the mean and standard deviation are related to the basin characteristics of drainage area, mean annual precipitation, and percent forest cover, with the data regionalized geographically. Two sets of equations for north‐central and southern Idaho provide the best predictive results, with the equations for north‐central Idaho yielding multiple correlation coefficients in excess of 0.97. For the skew and serial correlation coefficients, maps of generalized regional values are prepared by the application of kriging theory, with the resulting maps illustrating the spatial variability of these statistics. The developed equations and maps can be used to estimate annual flow statistics at ungaged locations throughout the state.