Groundwater/surface water interaction in the Raisin River watershed, near Cornwall, Ontario.

A field study was conducted in 1994 and 1995 to understand the interaction of groundwater and surface water in the Raisin River watershed, near Cornwall, Ontario. The Raisin River lies within an agricultural region which relies heavily on groundwater use. The regional groundwater supply is predominantly from a limestone aquifer which underlies various surficial deposits (primarily glacial till). Groundwater movement appears to be in a southeasterly direction, towards the St. Lawrence River. Seepage meters, mini-piezometers, and a falling head permeameter were used to (i) measure the flux of groundwater into (positive seepage) or out (negative seepage) of the Raisin River, and (ii) measure the hydraulic conductivity of the Raisin River sediments. Measurements were made at thirteen sites within the watershed. To identify the source of groundwater and study processes of streamflow generation during storm runoff, surface water, groundwater, and rainwater samples were collected for environmental isotopes (oxygen-18 and deuterium). Raisin River discharge data were also analysed. Seepage measurements and hydraulic conductivities exhibit significant variability. The coefficients of variation for seepage measurements ranged from 20.3 to 392%, and for hydraulic conductivity from 0 to 161%, depending on the site. Seepage flux ranges from $2.23\times10\sp{-6}$ to $\rm{-}9.82\times10\sp{-9}m\sp3m\sp{-2}s\sp{-1},$ and hydraulic conductivity ranges from 10$\sp{-6}$ to 10$\sp{-9}$ ms$\sp{-1}$ (a negative seepage flux indicates groundwater flow from the aquifer to the river). Environmental isotope analyses indicate that meteoric water is the source of local groundwater with a mean residence time of approximately 4 months. After a storm event, groundwater composed 63% of total stream discharge. The peak response in the river is approximately two days after a storm event. These variables indicate that groundwater/surface water relationships should be taken into account if decisions are made with respect to water quality or quantity. (Abstract shortened by UMI.