Ninepipe Reservoir Pothole 



Climatic setting. The net annual precipitation balance for the 

 Ninepipe Reservoir area (from the MAPS database) is -18 inches, 

 placing this site toward the middle of the range of evaporative 

 intensity shown by sample sites of the intermontane valleys. Mean 

 monthly precipitation for the St. Ignatius climatic station shows 

 relatively even distribution with a maximum in May and June. Total 

 precipitation for the St. Ignatius station shows the three-year 

 running average remaining near or above the long-term average from 

 1980 through 1993. Total precipitation in 1993 (the year prior to 

 sampling) exceeded the long-term average by about 3 inches. 



Geologic setting. The Mission Valley generally is underlain by 

 glacial sediments deposited by the southward advance of the late 

 Pleistocene lobe which occupied the Flathead Lake basin. Sediments 

 in the Ninepipe area include till of different textures, 

 glaciolacustrine sediments and outwash in complex stratigraphic 

 seguences. Regional source areas for glacial sediment are mainly 

 underlain by metasedimentary rocks of the Proterozoic-aged Belt 

 series, including calcareous and dolomitic lithologies. Generally 

 the kettle-pitted surface underlying the Ninepipe National Wildlife 

 Refuge and surrounding areas is composed of till of relatively low 

 permeability. Permeable aguifer gravels within the upper 200 feet 

 of the glacial seguence support high-yield wells nearby. 



Hydrologic type. The WET53 wetland occupies a small ice-block 

 depression (kettle) within the kettle wetland complex surrounding 

 Ninepipe Reservoir. The wetland receives surface runoff from a 

 restricted area and possibly shallow ground-water inflow from the 

 Post E Canal , situated close by and apparently upgradient from the 

 WET53 wetland. The site is believed to lack surface-water drainage 

 under the present conditions. The permanence of this site is 

 uncertain; the sample collection, however, occurred later in the 

 summer during a generally dry year. 



Basin characteristics. The surface catchment and relief of this 

 site are minimal, though impossible to define with any precision 

 using available maps. The water depth is unknown but inferred to 

 be no more than a few feet. Ground-water relationships are also 

 unknown; local pond outflow (restricted by low hydraulic 

 conductivity) probably occurs under at least some conditions. It 

 is possible (though not considered likely) irrigation canal seepage 

 supports ground-water inflow to the site. 



Water chemistry. At the time of sampling, the WET53 site contained 

 alkaline "oligosaline" magnesium-carbonate water. WET53 exhibited 

 the highest reacting percent of magnesium seen in the sample set. 

 It also contained an unusually high fraction of chloride for a site 

 of relatively low salinity. Eguilibrium calculations indicate 

 substantial oversaturation with respect to carbonate minerals; the 

 poor charge balance shown by this analysis places these 



