Groundwater contributions to discharge in a permafrost setting, Big Fish River, NWT, Canada

Groundwaters, surface runoff and river discharge have been studied at the Fish Hole area of the Big Fish River catchment, near Aklavik, N.W.T., to quantify the seasonal variations in groundwater contributions to baseflow in a permafrost basin. Geochemical and isotope methods are used to distinguish three principal water types: (1) subpermafrost Na-Cl thermal waters (16 degreesC) discharging from bedrock along the river, (2) shallow, Ca-SO4 groundwaters, and (3) low-salinity, Ca-HCO3, suprapermafrost drainage. Cl and SO4 concentrations in river water show that baseflow is largely derived from groundwater sources (Na-CI and CaSO4 components), with less than 30% contributed from surface water runoff in any season. Thermal groundwaters discharge year-round at a calculated 1.6 m(3) s(-1). The shallow, Ca-SO4 groundwater is the dominant component of baseflow in summer but is absent in winter baseflow. Discharge analysis based on a single flow measurement (25.5 m(3) s(-1) in June, 1997) and Cl-dilution allows calculation of total river discharge. This is shown to vary from a low of 2.2 m(3) s(-1) in the winter, to 1050 m(3) s(-1) during early spring melt.