Estimation of key parameters in model for solute transport in rivers and streams

Abstract

The exchange mechanisms associated with transient storage zones of a natural heterogeneous environment are often modified by unsteady water flux in the transient storage zone. This phenomenon can play an important role in the mass exchange between the free flowing water zone and the transient storage zones and may be the cause of the plateau region of the tail of observed concentration curves in natural streams. Deterministic interpretation methods are often used to generate the shape of the solute concentration curves in natural streams based on representations of transient storage exchange. Although many models are available to predict the parameters for the deterministic interpretation method, none can be used with confidence unless previously calibrated in the particular river reach under consideration. Therefore, the availability of reliable means for the provision of these parameters is usually the primary difficulty in the prediction of the rate of movement, dilution, and mixing of solute in rivers and streams. Measured tracer-response curves produced from the injection of a known quantity of soluble tracer provide one means for obtaining the requisite parameters. In this work, we advance an alternative approach based on the use of hydraulic and geometric information that are easily obtained in natural streams. Empirical equations used to predict the parameters are also analyzed to evaluate their behavior in representing solute mixing in natural streams with transient storage zones. Finally, the present proposals are validated against field meausrements of the solute concentration curves of chloride along a 1.2~km reach of the Shingobee River, Minnesota, U.S.A.