INTEGRATION OF DISPARATE DATA INTO GROUNDWATER MODELING FOR WATER SUPPLY AND STREAMFLOW SUSTAINABILITY IN THE PUGET SOUND REGION

The U.S. Geological Survey (USGS) Washington Water Science Center, in cooperation with the Washington State Department of Ecology (Ecology) and local cooperators, is developing numerical models of groundwater flow for several basins in the Puget Sound lowlands of Washington State. Local stakeholders in these basins have raised concerns that potential future groundwater development could affect stream baseflows, and adversely impact the viability of threatened salmonid species. However, any restraint on future use of groundwater for residential and commercial development could damage the local economies of the region. For these conflicting objectives, it is vital to obtain the best estimates of available groundwater supplies in light of surface water needs. The poster highlights the data that were integrated into two regional models of groundwater flow, in the lower Skagit River valley and the Clover–Chambers Creek Watershed.

Data collection for the projects included establishing groundwater and surface-water monitoring networks to characterize spatial and temporal variations in water levels and streamflows, and to document interactions between aquifers and streams. Drillers' log data from databases maintained by the USGS and Ecology were interpreted, in conjunction with previous hydrogeologic interpretations by the Washington State Department of Natural Resources and other researchers, to construct hydrogeologic frameworks for each numerical model. LiDAR data were used to construct digital elevation models.

The groundwater flow models required data for: 1) well withdrawals by public water systems and individual residences, as estimated by the Washington State and local Departments of Health, as well as County Assessor databases and Census estimates; 2) a representation of the complex hydrogeologic framework; 3) recharge based on a precipitation, surficial geology, forest cover, and impervious surfaces, augmented by septic system return flows; 4) stream and lake extents and stage elevations; and 5) submarine ground-water fluxes into Puget Sound. The models were calibrated first to average water levels and baseflows to simulate steady-state conditions, and then expanded to include monthly transient conditions.