Ninepipe Reservoir Outlet 



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 interraontane 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. Water supply in Ninepipe Reservoir, however, 

 is largely dependent on the storage and controlled release of 

 runoff from mountain snowpack. Hence the low-elevation St. Ignatius 

 station cannot be expected to closely reflect hydrologic conditions 

 in the reservoir or associated wetland areas. 



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 

 sequences. 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 is composed of till of relatively low permeability. 

 Permeable aquifer gravels within the upper 200 feet of the glacial 

 sequence support high-yield wells nearby. 



Hydrologic type. The WET52 site is within a ponded riparian area 

 fed by the regulated outflow from Ninepipe Reservoir. Inflow to 

 the reservoir is largely imported water from streams draining the 

 Mission Mountains to the east, routed to Ninepipe via other 

 reservoirs and an extensive ditch system. 



Basin characteristics. The natural catchment of Ninepipe Reservoir 

 includes a relatively small area along the Mission Mountain front. 

 As managed, the catchment includes upper Post Creek, draining the 

 highest peaks of the Mission Mountains. 



Water chemistry. The WET52 sample shows dilute calcium-bicarbonate 

 composition with near-neutral pH. Mineral equilibria indicate 

 slight undersaturation with carbonate phases. Ammonium, 

 phosphorous and total organic carbon concentrations rank mid-range 

 among similarly classified sampling sites. Chromium was reported 

 at the detection limit (one of only 3 western samples with 

 reportable concentrations), and the iron concentration ranked 

 toward the upper end of the range shown by this class of sampling 

 site. Other trace elements were reported to be below detection 

 limits. 



Chemical history. No other chemical data are known from this site. 



