Summer stormflow from a 1.57 km2 headwater basin in southern Ontario, Canada, which contained a 0.31 km2 valley-bottom, treed spring-fed swamp, was examined in 1987 and 1988. A large and annually constant groundwater flux emerged in the swamp, producing permanent saturated areas and a series of surface streamlets. The streamlets play a significant role in the production of an overland flow component of storm runoff. Stormflow volume produced by the basin was very small (runoff coefficients less than 0.01), but because of the well developed surface ‘streamlet’ system stormflow response and recession were rapid. Stormflow yield was equivalent to the depth of precipitation incident on the surface streamlets and stormflow volume was directly proportional to the volume of rain, indicating the size of the saturated zone was constant and not influenced by the storm rainfall. There was no evidence of groundwater being a major contributor to storm runoff. However, because groundwater controls the development of the surface streamlets and swamp saturation, seasonal groundwater hydrology and storm surface hydrology are inseparable.

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