| Summary: | The Shimbashi site of the Taber Irrigation Return Flow study occupies a 28 square-kilometer agricultural environment in southern Alberta. The site is situated in a bend of the Oldman River and therefore is encompassed by the river on 3 sides. Various types of existing and field-generated geologic, geophysical, and hydrologic data were employed to fully evaluate the groundwater flow regime of the study site. Mathematical modelling was carried out to analyse the long-term effects of fertilization on the groundwater and river water quality.
Bedrock of the Foremost Formation subcrops throughout the whole of the Shimbashi study site. This is overlain by 3 to 10 meters of Saskatchewan gravel and sand. The Saskatchewan gravels are covered by approximately 40 meters of glacial deposits consisting of till and outwash sands.
The water table over the site generally slopes down towards the river valley wall as a subdued reflection of the topography. A channel in the surface outwash sands in the northern part of the site causes a local depression in the Water table. Another larger depression occurs to the south and is caused by a channel of outwash sands buried by till.
There are two main routes the groundwater can travel to the river. Much of the groundwater entering the river has moved through the outwash sands that cover the north half of the site. Water infiltrating the tills, which underly the outwash sands and which occur at the surface in the south, moves essentially vertically downward into the Saskatchewan gravels and sand. Once in the gravels the water flows into the river.
Mathematical modelling indicates that nitrates are already entering the river in limited amounts. Fertilization of lowland areas near the river results in the introduction of nitrates into the river within 3 years. Contaminated water in the suraface sands is also entering the river. Nitrate concentrations in this water will remain low unless additional acreage comes under irrigation. Nitrates that move through the till will not reach the river in significant amounts for 5 to 50 years.
Recommendations for future research at the Shimbashi site include field testing to evaluate the dispersivity of the sands and till, the installation of additional piezometers, a laboratory investigation of the cation exchange potential of the till, and a monitoring program of the river water quality. === Science, Faculty of === Earth, Ocean and Atmospheric Sciences, Department of === Graduate
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