Department of Geology
Eastern Washington University
Recent Masters theses in Geology
A BASELINE WATER QUANTITY INVESTIGATION OF THE
WEST MEDICAL LAKE DRAINAGE BASIN,
SPOKANE COUNTY, WASHINGTON
Nasir M. Aziz
Abstract
The primary purpose of this study is to determine the physical
characteristics of the West Medical Lake drainage basin and its
relationship to the surface water and groundwater system. Based on this
information, a hydrologic budget for the lake was calculated for the period
between January 1994 and December 1994.
West Medical Lake is located in Spokane County, Washington, and sits on
basalt bedrock with unconsolidated silty-clay alluvium at the north and
south ends. The area of the drainage basin is 2.94 km2 (1.84 mi2). Two
wastewater treatment plants discharge effluent from Lakeland Village and
Eastern State Hospital to the lake throughout the year. There is no other
source of surface water inflow to the lake, but they remained dry
throughout the study period. Other sources of inflow into the lake are
groundwater flow and direct precipitation. Water loss from the lake occurs
through evaporation, groundwater outflow into the basalt bedrock and
alluvium, and by irrigation. The water budget for West Medical Lake was
determined by monitoring changes in the lake stage, measuring effluent
discharge from the treatment plants, measuring changes in water level in
piezometers installed in the alluvial aquifer, and using precipitation and
evaporation data.
The change in lake storage was estimated by monitoring the lake stage.
The lake dropped 0.3 m (0.96 ft) overall between January 1994 and December
1994, losing 148,816 m3 (5,254,805 ft3) of water. The highest stage
occurred in April 1994 and May 1994 at 738.6 m (2,422.64 ft) elevation.
The lowest stage was observed in October 1994 which was 737.8 m (2,419.84
ft). The average stage of the lake was 738.26 m (2,421.5 ft).
The largest source of water inflow to the lake was from the basalt aquifer
system which accounted for 531,042 m3 (18,751,476 ft3) of water, which is
47% of the total annual input budget. Direct precipitation added 314,197
m3 (11,094,518 ft3) of water to the lake which is 26% of the total annual
input budget. The effluent discharge from wastewater treatment plant 1 and
2 into the lake was 223,792 m3 (7,902,273 ft3) and 131,351 m3 (4,638,102
ft3) respectively. Collectively, both the plants accounted for about 27%
of the total annual input.
Evaporation accounted for the loss of 781,511 m3 (27,595,708 ft3) of lake
water comprising 65% of the total annual output. Water lost to basalts was
389,589 m3 (13,756,674 ft3) which is about 25% of the total annual output
budget. Irrigation accounted for the loss of 177,954 m3 (6,283,689 ft3) of
water which is about 10% of the total annual output budget. A minor amount
of water, 144 m3 (5,100 ft3) was lost through the unconsolidated alluvial
aquifers at each end of the lake which is calculated to be only 0.3% of the
total annual output budget.
The total water input to the lake for 1994 was 1,200382 m3 (42,386,369
ft3), and the total output was 1,349,198 m3 (47,641,172 ft3), resulting in
a net loss of 148,816 m3 (5,254,805 ft3) of water for the study period.