HEAT TRANSPORT THROUGH A MEANDER NECK

The hyporheic zone has been defined as the saturated sediments and interstitial spaces beneath streams that receive water from the surface. This zone contains a mixture of surface (at least 10%) and ground water and distinctive biota. To better understand ground water and surface water exchanges, hydrological tracers are often used. A convenient and non-invasive tracer is heat transport. By analyzing the natural variation of stream temperature patterns and the resulting exchange of heat with the subsurface, the interactions between ground and surface water may be better understood.

This study used heat transport coupled with ground water flow as a parameter to investigate the interactions between the ground water and surface water of a stream and a meander neck. More specifically, the effects of diurnal temperature cycles in surface water on the water beneath a meander neck were examined and modeled. A physically based model designed to predict heat transport during steady state and transient conditions was produced. Heat transport was simulated through a meander neck of a third-order, low-gradient, meandering stream, using the U.S. Geological Survey's energy transport computer program VS2DHI. The horizontal two-dimensional heat flow model was used to help discern the stream and ground water flow exchanges. Temperature and ground water elevation data recorded in three wells across the meander neck were used to help calibrate the model. The recorded data indicated that within the middle of the neck, the temperature was not influenced by diurnal variation or in response to storm pulses. The model was used to determine 1) whether heat is transferred through the neck in the response to bypassing stream flow and 2) whether short term variations of heat are transferred into the meander neck at the outer margins. Initial results from a transient state model illustrate the dominance of stream water within the meander neck study area (>10% requirement for a hyporheic zone) and short term temperature variations are shown at a depth of 0.68 meters at the surface influence of the meander.