These dams would normally be empty, for they could be pierced by a pipe which would carry about one-and-a-half times the normal flow of the stream. However, when much more water came down from the catchment area above, its flow through the pipe would be restricted to one-and-a-half times its normal flow; the excess water would be held back and released gradually, so helping to prevent flooding in the river downstream.
Such dams could usually be quite small; they could be built easily with a bulldozer and grassed over; they would not be expensive to make; and, as they would usually be on upland pastures, they should be of very little nuisance to the farmers.
It would be interesting to know whether the river authorities have considered this comparatively cheap method of flood control.
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