This report is a preliminary assessment of the geological and groundwater investigations of the Marmot Creek basin undertaken by the Research Council of Alberta. This basin is a watershed management study basin in spruce-fir forest. Soils, vegetation, and surface hydrologic characteristics of the basin are being studied by co-operating government agencies.

Eighteen water-table observation wells and eight piezometers were installed to measure fluctuations of the water table, establish phreatic divides, and define limits of the groundwater researvoir. Wells and piezometers have not been installed in the upper part of the basin because of difficult access. Groundwater records span almost two years for most wells, whereas streamflow and weather data cover up to four years.

Marmot Creek basin is formd in dominantly fine-grained, well-cemented Mesozoic sedimentary rocks of generally low permeability. The bedrock is covered by glacial materials and colluvium as much as 100 feet thick in places with high apparent infiltration characteristics. Because of the lack of subsurface information for the mid-slopes and upper part of the basin, thicknesses of surficial deposits and surface area of the basins contributing to base flow during low-flow recession periods are approximations. The groundwater researvoir appears to be largely unconfined, being recharged directly by precipitation and depleted to supply stream base flow.

A mean groundwater-stage hydrograph was prepared to show mean water-table elevation for the wells with complete records. The hydrograph is judged to cover the average range of fluctuation of the water table although the wells used do not penetrate all the surficial deposits. Mean groundwater stage was plotted against base flow for low streamflow recession periods. This curve

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is nearly linear for low flow periods. The rating curve and the mean groundwater-stage hydrograph were used to determine the base-flow contribution to streamflow as recorded at the outlet of the basin. Streamflow seems to be strongly influenced by the sub-basin characteristics.

An annual hydrologic budget was calculated, based on 1965 and 1966 stream records, and an estimated gravity yield, for the interval between times when the vadose zone was saturated and surface-moisture storage was negligible. Approximate precipitation was 35 inches of which 59 per cent formed stream-flow, whereas 43 per cent was used by evapotranspiration; the two per cent deficit was made up from groundwater storage.

A groundwater budget was calculated for the same time interval based on the mean groundwater hydrograph and calculated gravity yield. Thirty four per cent of the streamflow was base flow, and 61 per cent of the total evapotranspiration loss was from groundwater; the remaining 39 per cent of evapotranspiration was supplied from the vadose zone. Potential evapotranspiration calculated by the modified Penman method was about 12 per cent higher than the open water evaporation (determined from corrected Class A pan data for June, July, and August, 1965) and was as large as previous annual estimates for this area.

Stream waters and groundwaters within the basin are of the calcium and magnesium bicarbonate type. Concentration of dissolved solids in stream waters is proportional to the base-flow contribution to stream discharge.

Additional investigation is required to determine the effects of soil freezing on water-table fluctuations, the amount of underflow at sub-basin stream discharge stations, to measure fracture permeability in shale members, to measure the gravity yield of surficial materials, to evaluate networks of small-diameter piezometers and to assess chemical changes in groundwater.

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