Runoff Process of a Subarctic Canadian Shield Lake Stream System

Abstract

<p>Many lake-stream networks consisting of numerous lake basin elements linked by surface flow channels occupy Precambrian Shield and lowland areas in the boreal region. To investigate the processes causing flow generation and seasonal severance of flow connection in the lake-stream system, a chain of lakes in northern Canada was studied in 2004. Water balance shows that rapid and substantial runoff from the local basin slopes during the snowmelt period led to a rise of lake levels above their outlet elevations to generate outflow. Continued summer evaporation caused draw down of lake storage below the outflow thresholds, represented by the lake outlet elevations. Outflow ceased and the lakes became disconnected. Summer rainfall in a semi-arid environment was insufficient to overcome storage deficit to re-establish flow connectivity among all lakes. Individual lake outflow generation is dependent on the rate of runoff delivery, the initial antecedent storage level with respect to the critical outflow threshold level and the ratio of catchment to lake area. For the drainage system as a whole, streamflow interruption or continuity depends on linkage of its lake-stream sub-units. The principle of fill and spill governs runoff generation and flow connection between the lake elements. This principle is applied to model the flow along a chain of lakes, taking account of antecedent storage in individual lakes, their storage change calculated through water balance and the thresholds to be exceeded for outflows to occur.</p>