Hydrologic Investigations of Groundwater and Surface-water Interactions In Subarctic Alaska: Paper presented at the 12^th Northern Res. Basins/Workshop (Reykjavik, Iceland – Aug.23^rd -27^th 1999)

Dynamic interactions between rivers and adjacent aquifers can significantly affect near-bank geochemistry and processes associated with natural attenuation of contaminants by mixing water or introducing oxygen or nutrients. During 1997 and 1998 in a study near Fairbanks, Alaska U.S.A, the hydrologic conditions in the Chena River and in the adjacent groundwater were monitored. The river stage, groundwater elevations, and the water chemistry and temperature in both river and groundwater were measured. In the spring of 1997, the groundwater gradient close to the Chena River reversed causing surface water to enter the aquifer. Changes in temperature, specific conductance and alkalinity were used to determine the extent of bank recharge. For approximately one week during spring snowmelt of 1997, surface-water influx from the Chena River occurred approximately between the depths of 5.33 m and 9.1 m below ground surface. The effects of bank recharge extended at least 6.1 m but not to 30.5 m from the banks of the Chena River into the aquifer. Bank recharge caused 64 to 68 per cent of the groundwater, 6.1 m from the bank at a depth of 6.78 m to be displaced by surface water influx. Peak flows during 1998 were not high enough to cause flow reversals.