Combining Hydrologic and Geochemical Methods to Quantify Sources and Volumetric Contributions of Baseflow

A cohesive definition and robust understanding of stream baseflow remains elusive, particularly at broad temporal and spatial scales in snowmelt dominated watersheds. In these types of settings, baseflow is quantified (or estimated) using a number of approaches including hydrograph separation based on gaged streamflow, watershed and groundwater modeling, and chemical transport partitioning. In western US seasonal snowmelt-dominated watersheds, runoff is the primary contributor to streamflow. However, many separation methods incorporate the seasonal snowmelt runoff generation as baseflow. The question remains whether this baseflow is an artifact of the algorithm used or an accurate assessment of the groundwater flow processes that are altered during snowmelt induced recharge. We used a combination of hydrologic and geochemical hydrograph separation methods to estimate the spatial discretization and volumetric contribution of baseflow and spring discharge in a northern Utah watershed. Results of the various separation techniques were evaluated from continuous streamflow records, discrete stream discharge measurements, and geochemical indicators of in-stream conditions. Results suggested that the majority of baseflow inputs to the watershed are constrained to the catchment headwaters. The comparison identifies strengths and weaknesses in both the separation methods and data collection choices used to elucidate baseflow separation. The benefit of this study is that it offers general suggestions for baseflow separation, a first-order assessment of data-collection that will increase confidence in baseflow estimates and points to potential methods for scaling up to regional estimates. We further compare the results from the baseflow separation in Utah to multiple baseflow estimation results from the Tomorrow River in Wisconsin.