Continuous estimation of baseflow in snowmelt-dominated streams and rivers in the upper Colorado River Basin: A chemical hydrograph separation approach

Abstract

Effective science-based management of water resources in large basins requires a qualitative understanding of hydrologic conditions and quantitative measures of the various components of the water budget, including difficult to measure components such as base flow discharge to streams. Using widely available discharge and continuously collected specific conductance (SC) data, we adapted and applied a long established chemical hydrograph separation approach to quantify daily and representative annual base flow discharge at 14 streams and rivers at large spatial (> 1000 km2 watersheds) and temporal (up to 37 years) scales in the Upper Colorado River Basin. On average, annual base flow was 21-58% of annual stream discharge, 13-45% of discharge during snowmelt, and 40-86% of discharge during low-flow conditions. Results suggest that reservoirs may act to store base flow discharged to the stream during snowmelt and release that base flow during low-flow conditions, and that irrigation return flows may contribute to increases in fall base flow in heavily irrigated watersheds. The chemical hydrograph separation approach, and associated conceptual model defined here provide a basis for the identification of land use, management, and climate effects on base flow.