WATER LEVELS IN CANTERBURY

Press, Volume LXXXV, Issue 25738, 25 February 1949, Page 8

WATER LEVELS IN CANTERBURY

LITTLE INFLUENCE FROM RIVERS GEOLOGIST’S SUMMARY

Ground water levels in Canterbury were related more to local rainfall records than to the flow of rivers, said Mr B. W. Collins, of the New Zealand Geological Survey, in a paper for the Pacific Science Congress. “The opinion has been expressed by geologists, and is still commonly held by the general public, that ground water in the Canterbury plains (including the artesian water of the Christchurch area) <is largely supplied by percolation from the major rivers,” he said. “Records of water levels in wells, which have been kept for some years, show little or no correlation with river flows, but a high degree of agreement with local rainfall records. “It is only near the rivers (within about a mile k>r less) that well water levels are significantly affected by river water level. The present gener-ally-high stage of the water table over much of the plains area of the province seems to be mainly caused by a seriey of years of greater-than-normal rainfall, rather than to other suggested causes such as leakage of irrigation water or aggradation of the river beds, though these and other factors may have combined to aggravate the position. “In many parts of the Canterbury Plains water supplies for both domestic and stock use are a major problem for settlers. Rainfall is only moderate or even low, and the rivers are widely separated and in many places deeply entrenched. Where the water table is more than about 20 or 30 feet below the surface few wells have been sunk, and its depth is frequently not known. Many settlers are unwilling to try sinking wells and depend on gainwater and open water races supplied by creeks in the foothills or from intakes on the main rivers. “Earth resistivity tests in the Methven district have recently given very encouraging results in determining the depth to the water table. where ground water may be reached within reasonable depths, it may be found worthwhile constructing drilled wells, since few wells in Canterbury have failed to deliver adequate supplies of water from depths only a few feet below the water table. As far as is known the water is everywhere of good quality, except in a few areas, near swamps, where it may be contaminated by rotting vegetation.”