The process to develop a watershed plan update in the Little Spokane River Basin (WRIA 55) as required by the new Stream Restoration law, RCW 90.94, is currently underway. A transient integrated groundwater and surface water model (GSFLOW) was developed to represent the complex geology underlying the watershed and the three-dimensional groundwater flow system. This presentation will focus on the use of a sophisticated water demand model in conjunction with the GSFLOW model to assess impacts from future permit exempt wells on low flows in the Little Spokane River and its tributaries, evaluate the use of managed aquifer recharge to offset projected impacts, and assess stream flow benefits from the retirement of existing water rights.
The assessment of mine or quarry development requires a multi-disciplinary approach to address the range of water-related concerns. Integrated surface water and groundwater models such as GSFLOW can address the complete hydrologic cycle in a manner that rigorously addresses the processes, spatial and temporal interactions. The integrated simulation of the gold mine, located in Northern Canada, illustrates the importance of the snowpack and snowmelt on both the surface and groundwater components of the transient water balance. The sophistication of the integrated approach provides models that are both hydrologically complete and significantly more flexible. The approach clearly represents the future of mine impact assessment.
Spokane Water Bank
The Little Spokane River (LSR) watershed covers portions of Spokane, Stevens, and Pend Orielle counties. The hydrologic and hydrogeologic conditions in the LSR watershed are highly variable; previous studies indicated that there is significant interaction between groundwater and surface water. Accordingly, an integrated GSFLOW model was developed to simulate surface water and groundwater flow. Surface water rights were represented as stream diversions and groundwater rights were aggregated to model cells. Once calibrated, the model was applied to simulate the effects of the increased domestic water use on streamflow, quantify the impacts of future climate change on the water balance, and evaluate the effectiveness of aquifer recharge projects on increasing baseflow at the outlet of the basin.