Laserfiche WebLink
<br />c <br /> <br />Ground-WaterISurface-Water Interactions <br />and Water-Resources Sustainability: <br />Examples from the Northwestern United States <br /> <br />The effects of ground-water withdrawals on streamflow and spring discharge have become a major concern in parts of <br />the Northwestern United States as continuing population growth increases the demand for water and pressures mount on the <br />water resources to meet minimum instream-flow requirements for recreation and for fish and wildlife habitat. Examples from <br />Washington and Idaho illustrate some of the complexities In how ground.water pumping affects surface-water resources. <br /> <br /> <br />PUGET SOUND LOWLAND, WASHINGTON <br /> <br />A numerical model of a hypothetical basin in the Puget <br />Sound Lowland of western Washington was used by Morgan <br />and Jones (1999) to illustrate the effects of ground-water <br />withdrawals on discharge to streams and springs in small <br />basins typical of the region. The hypothetical basin shown in <br />Figure C-1 consists of glacial deposits and alluvial sediments <br />along streams that overlie low hydraulic-conductivity bedrock <br />(see Figure C-2). <br />The results of three simulations are used here to <br />illustrate the effects of pumping on streamflow for each <br />of three different locations of water withdrawal from a well: <br />(1) the unconfined aquifer near stream segment A, (2) the <br /> <br />unconfined aquifer about 6,000 feet from stream segment A, <br />and (3) a confined aquifer near stream segment A that is <br />separated from the unconfined aquifer by about 25 feet of low- <br />permeability till. The pumping well in simulation 1 and that in <br />simulation 3 have the same land-surface location. The three <br />simulations (simulations 1-3) are for steady-state conditions; <br />that is. the ground-water system has reached dynamic equilib- <br />rium with the pumping from the well. For each simulation. the <br />percentage of the ground water withdrawn that comes from <br />capture of discharge to streams and their associated springs <br />is shown in Table G-1 for five stream segments labeled A to E <br />in Figure C-1. <br /> <br />~x-. <br />""/ <br /> <br />EXPLANATION <br /> <br />........-- Stream <br />@ Stream-segment letter <br /> <br />Figure C-1. Three-dimensional perspective view of a hypothetical basin typical of the Puget <br />Sound Lowland showing topography, streams, and wellloeat/ons for pumping simulations. <br />(Modified from Morgan and Jones. 1999.) <br /> <br />36 <br />