Selected hydrographs and statistical analyses characterizing the water resources of the Arkansas River basin, Colorado

Hydrographs of annual precipitation from 30 stations, April 1 snowpack readings from 18 snow-survey courses, annual discharge from 46 streamflow gaging stations, and instantaneous water levels from 37 wells are presented to illustrate the temporal and spatial variability of the water resources of the Arkansas River basin in Colorado. Statistical analyses indicate no apparent time trends in annual precipitation or April 1 snowpack , but they do indicate declines in annual discharge for locations in the eastern part of the basin. A composite hydrograph indicates a negligible change in groundwater levels between 1930 and 1980 in the alluvial aquifer downstream from Pueblo. Generally poor correlation occurs between precipitation data and snowpack data (less than 0.40 for monthly data and less than 0.61 for annual data). In addition, precipitation data did not correlate very well with discharge (less than 0.57 for monthly data), leading to the conclusion that the typical streamflow conditions are affected little by direct precipitation. Main-stem discharge correlates quite well with snow-pack (as much as 0.85 for annual data), indicating its dependence on snowmelt runoff. (USGS)