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Reach scale and evaluation methods as limitations for transient storage properties in streams and rivers

2007; Wiley; Volume: 43; Issue: 10 Linguagem: Inglês

10.1029/2006wr005808

1944-7973

Anders Wörman, Przemysław Wachniew,

Groundwater flow and contamination studies

The value of stream tracer tests depends on appropriate experimental design, accurate evaluation methods and careful generalization of results with account taken to relevant limitations. This paper examines six calibration methods for transient storage models and effects of parameter errors on model generalizations. The residence time of transient storage and retardation factor varied a factor of 8 and 27, respectively, with the choice of method. Methods that emphasize the tail of the tracer breakthrough, such as optimization of log‐concentrations, are required to provide accurate estimates of transient storage parameters, whereas optimization using normal values can lead to substantial errors. Moment matching techniques require a solute mass‐recovery higher than about 70% for a reliable estimate of the storage capacity. The pumping model provided good estimates of the storage in the hyporheic zone under different stream discharges at two tracer test events with tritiated water in the Hobøl River, Norway. The accuracy of the evaluation of the transient storage parameters decreases with distance in the stream caused primarily by decreasing precision in the measurements and insufficient mass‐recovery. With distance, more and more time‐scales representing the hyporheic zone flow are also manifested as signatures of the tracer breakthrough. In a stream‐landscape groundwater system that is characterized by multiple residence time‐scales, stream tracer results are limited to specific reach distances and need to be supported by theory or other data when generalized to longer distances.