The Spokane Aquifer Washington

Author : Michael S. Johnson
Publisher :
ISBN 13 :
Total Pages : 444 pages
Book Rating : 4.:/5 (276 download)

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Download or read book Hydrology and Hydrogeology of Long Lake, Spokane and Stevens Counties, Washington written by Michael S. Johnson and published by . This book was released on 1992 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The geologic history of the Long Lake, Washington area has resulted in complex hydrogeologic settings, with regional hydrogeology dominated by coarse sands and gravels of high hydraulic conductivity (101 to 103ft/day). Quaternary depositional environments including periglacial, glaciolacustrine, glaciofluvial, fluvial and colossal glacial outburst floods have created a complicated stratigraphy, local heterogeneity characterized by wide variations in hydraulic conductivity, and locally complex and unexpected flow patterns. The Long Lake hydrogeologic system is defined as the surficial unconfined aquifers adjacent to the reservoir composed of these Quaternary sediments. It is a flow-through system, receiving ground-water inflow from the Spokane Valley-Rathdrum Prairie aquifer at its upstream end, and discharging to the Chamokane Creek system at its downstream end. Ground-water levels and gradients in the system were directly related to the stage of Long Lake, and approximated steady-state conditions from April1991 through December 1992 when the level of the reservoir varied by less than one foot. Gradients were directed consistently toward the reservoir (positive) at some aquifer study sites and consistently away from the reservoir (negative) at others. Ground-water response to the 1992 reservoir draft was rapid and profound, and was interpreted to be a function of drafting rates, aquifer characteristics and distance from the reservoir. During reservoir drawdown positive gradients increased rapidly, while negative gradients decreased and in some cases reversed. During reservoir refilling gradient reversals occurred at sites with positive gradients; these transient negative gradients eventually reversed again to positive as the reservoir was returned to full pool, and the system equilibrated back to approximately steady-state conditions. Extended periods of 13-foot winter drawdown of the reservoir proposed for macrophyte control should not adversely affect domestic wells of suffictent depth located within close proximity to the reservoir. Monthly hydrologic budgets constructed for Long Lake for the period February 1991 to January 1992 showed surface-water to account for 95 to 99 percent of total inflow and 96 to 99 percent of total outflow. For the entire study period, surface flows comprised 98.5 percent of total inflow and 98.6 percent of total outflow. Surface-water inflow was dominated by flows in the Spokane River, which contributed anywhere from 82 percent of total surface inflow in August to 96 percent in May. Monthly ground-water inflow to the reservoir ranged from less than one percent to approximately five percent of total inflows, and from less than one percent to almost three percent of total outflows. The highest percentages of ground-water inflow occurred in August (4.7%), the month of lowest surface-water inflow, and in January (4.9%) as a result of increased gradients during reservoir drawdown. Over the entire study period ground-water accounted for 1.4 percent of total inflow and 1.1 percent of total outflow. Precipitation and evaporation were insignificant in both the annual and monthly budgets."--Document.