Estimation of time‐variable fast flow path chemical concentrations for application in tracer‐based hydrograph separation analyses. Issue 9 (10th September 2016)

• Record Type: Journal Article
• Authors: Kronholm, Scott C.; Capel, Paul D.
• Is Part Of: Water resources research. Volume 52:Issue 9(2016:Sep.)
• Page Start: 6881
• Page End: 6896
• Publication Date: 2016-09-10
• Subjects: hydrograph separation -- base flow separation -- mixing model -- high‐frequency water quality data -- time‐variable end‐member concentration; Hydrology -- Periodicals; 333.91
• DOI: 10.1002/2016WR018797
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Mixing models are a commonly used method for hydrograph separation, but can be hindered by the subjective choice of the end‐member tracer concentrations. This work tests a new variant of mixing model that uses high‐frequency measures of two tracers and streamflow to separate total streamflow into water from slowflow and fastflow sources. The ratio between the concentrations of the two tracers is used to create a time‐variable estimate of the concentration of each tracer in the fastflow end‐member. Multiple synthetic data sets, and data from two hydrologically diverse streams, are used to test the performance and limitations of the new model (two‐tracer ratio‐based mixing model: TRaMM). When applied to the synthetic streams under many different scenarios, the TRaMM produces results that were reasonable approximations of the actual values of fastflow discharge (±0.1% of maximum fastflow) and fastflow tracer concentrations (±9.5% and ±16% of maximum fastflow nitrate concentration and specific conductance, respectively). With real stream data, the TRaMM produces high‐frequency estimates of slowflow and fastflow discharge that align with expectations for each stream based on their respective hydrologic settings. The use of two tracers with the TRaMM provides an innovative and objective approach for estimating high‐frequency fastflow concentrations and contributions of fastflow water to the stream. This provides useful information for tracking chemical movement to streams and allows for better selection and implementation of water quality management strategies. Key Points: A ratio‐based two‐tracer mixing model is applied to hydrograph separation Estimates of chemical concentration and flow are compared to actual values Fastflow chemical concentrations are estimated with high‐temporal frequency