CONTROL OF EROSION

Wairarapa Times-Age, 4 March 1940, Page 9

CONTROL OF EROSION

NOT BY ENGINEERING ALONE. “It is good to have news of the decision of the Hon R. Semple, Minister of Public Works, to give effective attention to the very important matter of erosion, - ’ says Captain Sanderson, president of the Forest and Bird Protection Society, “but it is hoped that the new methods of control flooding of rivers will be a great improvement on the mistakes which can be seen in a number of districts of the north and south islands. “The attempts to control turbulent rivers with stop-banks alone must fail because a river is always filling its bed even under natural conditions. When the watershed is denuded of its natural covering the process of bed-filling is very greatly hastened. “Many rivers naturally tend to obstruct their own courses by swishing and rolling debris downward from high country. Then a new channel is cut beside the obstacle, and the former process is repeated. That is why rivers run in tortuous courses.

“Engineers’ efforts to straighten river courses may appear to produce good results for the time being, but before long debris will again pile up in any such channel and sooner or later causethe river to attempt to resume its natural zig-zag course. In the end it will succeed despite the engineers.

“The proper procedure is to look for the trouble at its source and ascertain the cause of the river’s troublesome behaviour. This investigation will usually show that the cause of the destructive flooding is in the loss of nature’s protective covering on the watershed due to foolish burning of bush or scrub or unintelligent timber-milling. It has been truly said that the building of stop-banks on the lower-levels without taking any action in the high country is like maintaining an ambulance at the foot of a precipice instead of putting a fence at the top. Control of erosion requires much more than engineering. That call is for a well-plan-ned national policy which will give good heed to all aspects of the case.”