Medicine Ledce 



Climatic setting. The net annual precipitation balance for 

 Medicine Lake derived from the MAPS database is -24 inches, toward 

 middle of the range of evaporative intensity for sites in this 

 class. Based on analyses of evaporation pan data, this is a 

 considerable underestimate Medicine Lake's water deficit, and 

 points out the need to view the MAPS estimates only as relative 

 indicators of net site precipitation. Mean monthly precipitation 

 for the Medicine Lake climatic station shows a pronounced June 

 maximum. Annual totals for this station show apparent periodicity 

 with a 5 to 7 year cycle. Throughout the 1980s, the 3-year running 

 average remained below (often well below) the long-term average, 

 recovering in the early 1990s. In 1993 (the year before sampling) 

 precipitation exceeded the long-term average by more than 1 inch. 



Geologic setting. Medicine Lake occupies a large depression in the 

 sequence of late Pleistocene outwash sand and gravel forming the 

 Clear Lake aquifer. The composite thickness of the outwash gravels 

 is greater in the Gaf fney-Medicine Lake vicinity than elsewhere 

 along the Clear Lake outwash channel. Preglacial terrace gravel 

 aquifers are apparently incised by outwash sediments in the 

 vicinity of Medicine Lake, creating hydrologic linkages between 

 stratigraphically distinct aquifers and surface water bodies. 

 Glacial and sediments and preglacial alluvium are underlain at 

 depth by the early Tertiary Fort Union Formation. 



Hydrologic type. Medicine Lake is a natural ground-water discharge 

 area for the Clear Lake Aquifer which has been modified to 

 stabilize water levels and to accommodate water imports diverted 

 from Muddy Creek. Additional inflow is supplied by Lake Creek, 

 which delivers limited runoff and ground-water discharge to 

 Medicine Lake and other basins. Outflow from Medicine Lake to 

 Muddy Creek is also managed by control structures. Often the full 

 water right for the Big Muddy diversion cannot be exercised, 

 however, and the lake may go several consecutive years without 

 spilling surface water. 



Basin characteristics. The water budget of Medicine Lake is 

 dominated by ground-water inflow and by extra-basin imports from 

 Big Muddy Creek; neither is closely linked to the natural surface 

 water catchment of the lake. Regionally, evaporative losses from 

 Medicine Lake (and other lakes) are the predominant outflow 

 component of the Clear Lake Aquifer's water budget and are an 

 important influence on ground-water gradients and ground-water 

 flux. Imports of Big Muddy Creek water to Medicine Lake are 

 believed to have a corollary effect on the aquifer, stabilizing 

 ground-water levels in the vicinity of the lake. 



The U.S. Fish and Wildlife Service estimates the capacity of 

 Medicine Lake at "management elevation" at about 88300 acre-feet, 

 with an average lake depth of about 10 feet. From 1988 to 1993 

 year-ending lake volumes ranged from 66% to 75% of this management 



