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The Nelson Photo News



Combating Flash Floods

Flash flooding of the York Stream in the Nelson South area is infrequent, but when such floods do occur they create tremendous drainage problems for the Nelson City Council. To overcome these problems, the Council is constructing a flood detention dam across the stream about a quarter of a mile above Waimea Road. Its job will be to minimise peak flooding conditions and to retain the water behind it during heavy rainfall. Water in the stream and the surrounding area will find a controlled outlet (above) and will flow through a pipeline built under the dam to an outlet port. The holes in the pipe will also help to drain the area when the water reaches this height. At left are concrete drop structures. Excess water that may accumulate behind the dam will flow along an overflow channel into these boxes, thus preventing scouring.



This picture, taken above the dam site, gives a better idea of the scheme. Eventually the dam's height will reach the level on which the bulldozer (centre) is standing, and along that track the overflow channel will be constructed to take the excess water j banked up by the dam on the right of the picture. The drop boxes jean be seen at left and also, at bottom left, the end of the pipe. I line under the dam. The cow is not provided for in the overall scheme.