Data in these tables for streams with major reservoirs have been adjusted by adding upstream reservoir change-in-storage volumes and major diversions to the observed monthly streamflow volumes to reflect a "natural flow" condition. Reservoir evaporation and most diversions are not accounted for in the NRCS database listed here. The U.S. Geological Survey (USGS), U.S. Bureau of Reclamation (USBR) and Idaho Department of Water Resources (IDWR) are a source of most of the data presented. Streams without reservoirs and stations upstream of the reservoirs show monthly data as received directly from USGS archived records.
Snow graphs illustrate average monthly snow water and the chance of snowpack “recovery” for a given year. Snowpack recovery refers to the chance that snow water content will increase to reach average peak seasonal values (typically April) when accumulation is below average during core winter months (typically Nov-Feb). Data are sorted from low to high snow water, using first of the month values for January, February, and March to compare across the accumulation season, ending on April 1st. Stream flow graphs are included to show a simplified relationship between seasonal snow water and stream flow. Flow data is sorted by the month of April to illustrate peak of season patterns and sorted by year for comparison purposes.
Snow Indexes, Historic Snow Water Data by Basin, Idaho
Measuring the amount of water held in the snowpack in a given basin helps to better understand water storage and, in some cases, potential runoff volumes during the spring and summer months. Indexing the snow water values allows for easy comparison from year to year and for observing trends over time.