Ground Water Resources of British Columbia
Chapter 13 — Case Histories
13.1 GROUND WATER SUPPLIES USED IN AGRICULTURE
Ground water has been used for irrigation on a small scale in British Columbia since before 1900 when small domestic artesian wells were used to irrigate gardens. The first use of ground water for large scale irrigation depended on the development of the well screen and the arrival of electric power in rural areas. In British Columbia, the first use of ground water to supply a major irrigation district was in 1963 when a high capacity well was constructed at Oyama in the Okanagan Valley (Figure 13.1).
Figure 13.1 Intermontane valleys in the Southern Interior System showing
locations of Keremeos wells (adapted from Foweraker et al, 1985)
The change to ground water for irrigation supply was brought about largely by economic factors. In addition, there was a need to supply domestic quality water to residents in irrigation districts on a year-round basis. It was often found to be less costly to supply untreated water from wells in the district than to treat existing surface water supplies and to replace long canals and ditches with buried pipes for winter operation. More recently, ground water is used for irrigation where no other sources of irrigation water are available and in places where all available surface water has been allotted to existing water users.
Most of the large irrigation districts using ground water in British Columbia are located in the Okanagan Valley where a variety of fruit tress, grapes and commercial crops are grown. The use of ground water for irrigation to commercial crops (primarily raspberries and strawberries) in the Fraser Lowland has become significant in the last 10 years, but still represents only 10% or less of total water use.
A good example of the use of ground water for large scale irrigation in British Columbia is the Keremeos Irrigation District (Figure 13.1) located in the valley of the Similkameen River near the United States Boundary. The floor of the Similkameen Valley in this region is 1 1/2 to 2 km wide; the valley sides are very steep above low gravel terraces.
The Keremeos area was settled at the turn of the century and irrigation started in 1908. A large irrigation scheme that was built about 1930 used water flowing by gravity from the Ashnola River, a large tributary of the Similkameen River. When the irrigation system required major repairs in 1967, the feasibility of using ground water was investigated. The cost of a system based on ground water was found to be less than repairs to the Ashnola Surface Water System so the system was reconstructed using two well fields to supply the entire demand which reaches about 700 L/s. The present system was put into operation in 1973; two additional wells were added and minor changes to the system were made in 1978.
The nature of the surficial deposits filling the Similkameen Valley is known mostly from many water wells that have been constructed in the near-surface aquifer. A log from a 126 m deep test well shows two other gravelly sand aquifers separated by till below the upper gravel aquifer.
The upper aquifer which extends from near surface to 43 m is very productive so it is the only one being exploited. Recharge is mostly from the Similkameen River which is a meandering stream with a coarse gravel bottom and an average gradient over 51 km of about 2.6 x 10-3. A number of topographic features and geologic exposures show that the valley was the site of a huge flood of short duration at the end of the last glacial episode in the area about 10,000 years ago. This flood, and similar events in other valleys in Southern British Columbia, occurred when a dam of ice and glacial debris impounding a glacial lake suddenly broke. These floods were essentially erosive events but, at the end of the flood, large amounts of sand and gravel were deposited, especially at places where the valleys became wider. The upper aquifer may well be torrential gravel which is usually very highly permeable.
Two well fields (East and West) supply the Keremeos system. The East Well Field consists of 6 wells with a total pump capacity of about 438 L/s. The West Well Field consists of 4 wells with a total pump capacity of 263 L/s. All wells are 400 mm diameter except for one 200 mm well in each of the well fields. The 400 mm wells are completed with 300 mm pipe size stainless steel spiral-wound well screens. Specific capacities of the 400 mm wells vary from 30 L/s/m to 66 L/s/m of drawdown. Pump testing shows that the transmissivity at both well fields is about 1.4 x 10-1m2/s.
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