Evaluating the influence of hyporheic flows on solute transport using a numerical model

Abstract

Transport of solutes in streams are affected by multiple mechanisms and processes that include river morphology, turbulence, reaireation, and transient storage areas which include re-circulation zones, hyporheic flows and dead zones. The hyporheic zone is an active ecotone between the surface stream and groundwater. In this zone important exchanges of water, nutrients, and organic matter occur in response tovariations in discharge and bed topography and porosity. Is in this zone where water that is flowing in the stream channel flows into the subsurface materials of the streambed and then returns to the main stream, making the hyporheic zone a continuous link between the stream‘s channel and catchment. The dead zone is defined as a region of static or slowly moving water (i.e. backwater eddies, stagnant water at the bottom of pools, and flow through vegetation). Dead and hyporheic zones play a key role in controlling the water quality, for instance affecting the stream dissolved oxygen concentration, which ultimately controls the habitat suitability for a number of aquatic and riparian species. To evaluate the influence, effects and importance of hyporheic zone in the transport of solutes a field camping was conducted, where a series of Rhodamine injections were monitored in along a 271 m reach in Bear Valley Creek, ID, USA. The analysis of the dead zones and hyporheic flows was performed using the OTIS Model (One-Dimensional Transport with Inflow and Storage, USGS) where the governing equation underlying the model is the advection- dispersionequation with additional terms to account for transient storage, and first-order decay. Results showed that the includingtransient storage areas, in this casehyporheic and dead zones must be explicitly included in order to describe how solutes are transported in a stream whose bed present some degree of permeability.