On the behaviour of dynamic contributing areas and flood frequency curves in North American Prairie watersheds

This statistical study examines the impact of storage upon the frequency and magnitude of runoff in the hummocky glacially transformed landscape of the Canadian Prairies. When runoff production is unaffected by depressions, the shape of the runoff frequency curve resembles the shape of the precipitation frequency curve, adjusted for the effects of infiltration, evaporation, sublimation, and wind redistribution of snow. However, the shape and slope of the runoff frequency curve can be affected by storage thresholds associated with hillslope and wetland depressions, and reflect the number, size and spatial distribution of depressions in the catchment. A comparison of runoff frequency curves from catchments with or without depressions provides a useful indicator of the amount of water retained by surface depressions without recourse to detailed topographic mapping of the basins. Results obtained from this study provide valuable insights into the complex function of closed and intermittently contributing drainage basins.