Ground Water Resources of British Columbia
Chapter 13 — Case Histories
13.7 POOR MANAGEMENT OF AN AQUIFER SUPPLYING IRRIGATION WATER TO TWO RANCHES IN THE SEMLIN VALLEY EAST OF THE VILLAGE OF CACHE CREEK
An example of poor management of the ground water resource in British Columbia is that of the aquifer underlying the Perry and Semlin Ranches in the Semlin Valley east of Cache Creek.
The Semlin Valley is a high eastward sloping valley which extends from the Bonaparte River drainage on the west to the Thompson River drainage on the east. The Perry Ranch occupies the eastern part of the Valley; the Semlin Ranch adjoins it on the west. The Semlin Valley has been isolated from present day drainage by the downcutting of both drainage systems, probably in Pleistocene time. Irrigation water is brought into the western end of the Valley by ditches from Cache Creek, but the water from Cache Creek is not sufficient to irrigate all of the arable land in the valley.
In the late 1950s, the Perry Ranch started a search for ground water as a source of additional irrigation water. A dowser was hired and drilling was carried out on the north side of the Semlin Valley without success. In 1961, at the suggestion of a drilling contractor, a 200 mm diameter hole was drilled in the valley bottom. It encountered a thick, permeable gravel aquifer under about 27 1/2 m of glacial till. The aquifer was under artesian pressure and, after the casing had been perforated with a mills knife between 28.4 and 39.6 m, the well flowed at about 57 1/2 L/s. In 1965, another 200 mm diameter well was constructed using a 16.5 m length of slotted 150 mm diameter pipe instead of well screen. This was followed in 1970 by construction a 400 mm diameter well with a 300 mm pipe-size diameter well screen which was 15.2 m in length. The well constructed in 1970 was pump tested at 110.4 L/s.
In 1970, the adjacent Semlin Ranch started the search for ground water as a source of irrigation water. The geology at the Semlin Ranch is somewhat more complex than it is a short distance to the east on the Perry Ranch. Between 1970 and 1981, eleven holes were drilled on the Semlin Ranch. Five of these were completed as production wells to provide water for irrigation.
From the time of completion of the first Perry Ranch well in 1961, the artesian head in the aquifer in the Semlin Valley has declined steadily from its original level of 4.9 m above ground. The water has been used for irrigation but large amounts of water were wasted in the past when the wells were allowed to flow in the winter months to water cattle. For irrigation, water was pumped into open ditches and repumped to sprinklers in the fields; this practice led to additional losses.
As early as the mid-1960s, it was clear that the artesian aquifer was limited to the Semlin Valley in which the Ranches are located and that it was unlikely, because of its location and the dry climate, to receive much recharge. It was apparent that management of the aquifer would be required to deal with the problem of eventual aquifer depletion.
The aquifer depletion situation outlined has been further complicated by frequent changes in ownership of the Perry and Semlin Ranches in the period of rapid rise in the price of ranch land during the 1960s and 1970s. The high costs of financing the speculative purchases of the ranches, along with low prices for cattle and agricultural commodities, have brought about the end of profitable ranch operations in the Semlin Valley. Under these economic conditions, the present owners have no resources available to attempt to deal with the aquifer depletion problem by means of artificial recharge and water conservation. With proper management, the life of this important aquifer could have been prolonged and perhaps, with artificial recharge, may eventually be recharged and its life prolonged indefinitely. There is plenty of water in Cache Creek in the non-irrigation season for artificial recharge of the aquifer if an artificial recharge scheme can be designed.
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