EFFECTS OF SURFICIAL GEOLOGY ON STREAMFLOW DISTRIBUTION IN SOUTHERN ONTARIO

Abstract

The monthly streamflow distribution on four pairs of watersheds in southern Ontario was investigated. The dominant parent geological materials on the four pairs of watersheds were as follows: A, coarse-textured soils; B, moderately fine-textured soils formed on very fine sands and silts; C, medium-textured soils formed on till; D, fine-textured soils formed on till. The March–April runoff from the watersheds of fine-textured soils (D) was 56% of the annual runoff over a 9-year period, and from the watersheds of coarse-textured soils (A) it was only 34% of the annual runoff during the same time period. Larger amounts of groundwater recharge on watersheds of coarse-textured soils resulted in higher summer flows, more uniform seasonal flow, and reduced spring runoff extremes.The groundwater daily recession constant was likewise higher for the streams draining coarse-textured soils. The average estimated equivalent groundwater storage remaining when the monthly discharge was at a rate that was exceeded for 90% of the time, was as follows for the four geological classes: A, 0.267 in.; B, 0.090 in.; C, 0.035 in.; D, 0.007 in.