A case study to assess the potential for saline soil development due to irrigation

With the help of a generalized conceptual model for the formation of saline soil, we examine whether irrigation proposed for an area near Lethbridge, Alberta will compound an existing salinity problem. The geology of the site is characterized by weathered and non-weathered tills which overlie Cretaceous bedrock. Locally, preglacial sands and gravels occur along the axes of two bedrock valleys beneath the site. Piezometric data define local groundwater flow from west to east, following the regional topographic slope. However, the depth to the water table is extremely variable and controlled by the preglacial sand and gravel unit. The existing problem of soil salinity, which is restricted to the western part of the study area, is caused by the high water table and large quantities of dissolved mineral mass in the groundwater. In the central and eastern part of the area, the water table occurs at depths greater than 20m and saline soils have not formed. Flow modeling along a two-dimensional cross section confirms that the water table configuration and hence the distribution of saline soils is controlled by the preglacial deposits. Indications are that excess recharge due to irrigation will not result in a water table rise unless the quantity involved is considerably larger than the natural rate of recharge. Thus, irrigation will not contributed to a marked increase in the size of the area affected by the saline soil.