TIDE CONTROL STRUCTURE

Putaruru Press, Volume XXI, Issue 1237, 3 July 1947, Page 3

TIDE CONTROL STRUCTURE

PIAKO RIVER SCHEME Installation. Of Floodgates Opposed Replying to representations made by the Hauraki Catchment Board, \ Mr. E. Taylor, chief drainage engineer to the Department of Lands and Survey, has advised that, in his opinion, .the proposal Ifco construct a floodgate dam across the mouth of the Piako River, in lieu of the Pipiroa bridge, was impracticable. Apart from the fact that the coslt of building a structure of this kind on mud foundations would be enormous, the exclusion of the tide from the river would not improve the drainage conditions of tha low land on the river banks in wet weather. In dry weather the upland water would not be sufficient to fill the tidal compartment of the river when, the floodgates were closed, and consequently the high water levels in the river would be lower than high tide level in the Hauraki Gulf. The run-off produced by moderate rainfall in tho catchment area of GOO square miles would be sufficient to fill the tidal compartment of the river quicker than it could be filled by tidal inflow. Under these conditions the effect of the dam would be to raise the flood level in the river by tho amount of head required to operate the floodgates.

Interference With Navigation

Mr. K. S. Packwood, district commissioner of works, Public Works Department, agreed with Mr. Taylor’s views, and went further in stating that the lowering of the watertable during the dry weather might have a serious detrimental effect. He did nolb think the proposers of tha scheme realised that a major engineering work would be involved in installing floodgates capable of discharging a flood flow of 14,000 cusecs. The gates would have to be mounted on an impermeable structure founded on alluvium of a moat unsuitable character for the purpose, and necessitating underwater work and cofferdams on a largo scale.

Continuing, Mr. Packwood said Mr. Taylor had not referred to another aspect,- which was interference with navigation. It was quite unlikely that the Government or local bodies would agree to closing the river to small craft such vj towing launches, or barges, -d therefore some form of navigation lock would be needed The cost of installation and operation would be a considerable item. Prom Mr. Packwood’s observations and experience of hydraulic works, both in New Zealand and abroad, he felt the scheme was unsound in conception, that the benefits expected would not oe realised, and its very real disadvantages would do a disservice to the district.