|Goodrich, David - Dave|
Submitted to: University of Arizona Department of Hydrology and Water Resources Research
Publication Type: Research Notes
Publication Acceptance Date: 1/16/1997
Publication Date: N/A
Interpretive Summary: Groundwater plays an important role in sustaining surface water flows in dry periods with little rainfall. In wetter periods, surface runoff waters from storms interact with the groundwater aquifer system to help recharge it. Groundwater and surface water interactions play a very important role in maintaining riparian ecosystems, especially in arid and semiarid regions. However, groundwater systems typically change very slowly, often over months, while surface water systems often change rapidly from minutes to hours. This presents a difficulty in modeling the two systems together. It this study a model is developed for coupling the surface water and groundwater flow systems which is able to treat the great differences in their time response characteristics. The model was implemented in the Bill Williams River Basin in western Arizona and reproduces the observed streamflow patterns and the groundwater flow patterns.
Technical Abstract: A finite element numerical model is developed for the modeling of coupled surface-water flow and ground-water flow. The mathematical treatment of subsurface flows follows the confined aquifer theory or the classical Dupuit approximation for unconfined aquifers whereas surface-water flows are treated with the kinematic wave approximation for open channel flow. A Adetailed discussion of the standard approaches to represent the coupling term is provided. The fast time scale characteristic of surface-water flows and the slow time scale characteristic of ground-water flows are clearly established, leading to the definition of three dimensionless parameters, namely, a Peclet number that inherits the disparity between both time scales, a flow number that relates the pumping rate and the streamflow, and a Biot number that relates the conductance at the river-aquifer interface to the aquifer conductance. The model, implemented in the Bill Williams River Basin, reproduces the observed streamflow pattern and the ground- water flow patterns. Fairly good results are obtained using multiple time steps in the simulation process.