AQUIFER CHARACTERISTICS AND LONG-TERM GROUNDWATER LEVELS

Water-table depth, piezometric head, and precipitation were measured at nine sites in southern Alberta over a period of up to 28 years to determine the effect of irrigation on long-term groundwater levels. Irrigation and precipitation, mainly rainfall, directly recharged the unconfined aquifer. Temporary mounding of water occurred immediately following irrigation applications, causing short-term lateral groundwater movement. Downward hydraulic heads occurred during the spring and summer seasons and upward ones in the fall-winter period. High water tables were most frequent during May-July, when irrigation water was applied and precipitation was high. Highest levels generally occurred in soils with glacial till at depths less than 1.50 m from the surface. Water tables receded during the fall-winter period, most frequently to depths greater than 2.00 m, due chiefly to closure of irrigation canals. Above average precipitation was generally reflected in that year's average annual water-table depth, but there was a one-year lag before drought effects were evident. Irrigation method and management also affected average water-table depth. Depth to water table did not change appreciably over the duration of the study, increasing slightly but significantly at four sites and decreasing similarly at four other sites. As increasing water-table levels predominated at sites with till within 1.50 m of the surface, special management schemes need to be developed for these soils should salinization become a problem.