Research about Idaho;Montana;Nevada;Oregon;Utah;Washington;Wyoming

USGS2001

Estimating monthly and annual streamflow statistics at ungaged sites in Idaho

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.

Idaho;Montana;Nevada;Oregon;Utah;Washington;Wyomin↗

USGS2001

Evaluation of macroinvertebrate assemblages in Idaho rivers using multimetric and multivariate techniques, 1996-98

Macroinvertebrate assemblages and environmental variables were evaluated as part of the Idaho statewide surface-water quality monitoring program during 1996–98. Two assessment approaches were used to evaluate the macroinvertebrate data collected from Idaho rivers—biological metrics and multivariate statistical analyses. A total of 247 macroinvertebrate taxa were identified in semiquantitative riffle habitat (richest targeted habitat; RTH) and qualitative multiple habitat (QMH) samples, which were collected from 40 sampling sites. Riffles supported most of the taxa collected at all sites. One hundred and eighty-four taxa (74 percent of total taxa) were identified in the RTH samples. Taxa considered abundant in RTH samples included Oligochaeta, Baetis tricaudatus , Hydropsyche , Simuliidae, Chironomidae pupae, Cricotopus , Eukiefferiella , and Orthocladius complex. Comparisons of RTH and QMH sample types indicated little difference in various metrics evaluated; either sample type could be used to evaluate biological condition. Fourteen coldwater taxa were collected during this study at 12 sampling sites, representing only about 6 percent of all taxa collected and a frequency of occurrence of 30 percent for all sites. An evaluation of the Idaho Department of Environmental Quality invertebrate river index (IRI) identified statistically significant differences between highand low-quality sites, providing evidence that the index can successfully discriminate impairment. IRI scores for all sampling sites identified 25 percent of the sites with poor biotic condition and 68 percent with good biotic condition. Maximum temperatures at 62 percent of all sampling sites exceeded Idaho’s instantaneous coldwater temperature criteria of 22 ° C. No correspondence was evident between ecoregion percentages upstream from each site and macroinvertebrate assemblages. Multivariate analyses of RTH samples identified various environmental variables operating at different spatial scales that affect the macroinvertebrate assemblages in Idaho rivers. Six environmental variables—percent forested land, percent agricultural land, urban land, maximum water temperature, percent substrate fines, and stream gradient—were significant in describing variance in the macroinvertebrate assemblages. Two distinct groups of sites and associated taxa were identified: one represented high-gradient, coldwater, forested and rangeland sites, and the other represented sites influenced by human disturbance, indicated by increased percent substrate fines and increased water temperatures typically associated with agricultural and (or) urban land uses.

Idaho;Montana;Nevada;Oregon;Utah;Washington;Wyomin↗