Idaho Water Science Center

Modeling Idaho's Perennial Streams

Conducted in cooperation with the Idaho Dept. of Environmental Quality and
U.S. Bureau of Reclamation
Status: Complete

1:24,000 scale perennial streams model
Local, State, and Federal agencies often use the intermittent or perennial status of a stream to determine regulatory or management requirements. Stream status, as represented on USGS topographic maps, has not been as accurate or consistent as desired. This may be due to factors such as:
  • differences in adjacent maps such as compilation dates and cartographic standards
  • data entry errors

The ability to estimate perennial streams is important for two main reasons. First, the application of some Idaho water-quality standards depends on whether or not a stream flows perennially. Second, state water-quality managers sometimes go out to collect water samples from a stream classified as perennial only to find the streambed dry. The USGS has developed regional regression equations for Idaho streams for several low-flow statistics. Though not exact, the new model has proven far more accurate than the previous method of estimating perennial streams.