THE OPAWA RIVER.

Marlborough Express, Volume III, Issue 125, 11 July 1868, Page 4

THE OPAWA RIVER.

To the Editor of the Marlborough Express. Sir,— I request; through your kindness, to be allowed space in your valuable paper for this letter, relative to the above river. Should any effort of mine (though feeble), or any plan or suggestion [of mine, tend to lessen the calamity which has been, and is still increasingly so, spreading over the Wairau district and the town of Blenheim, through the overflow of the above river, I wish earnestly to place it before the public, hoping it may be of some service to the community at large. Various and numerous are the plans proposed for turning the Opawa river, one of which has been for some years contemplated, and which is to enlarge and extend the channel north of the Big Bush, known as Kelly’s ditch, up to the bend of the Opawa. I have recently made an estimate for opening a (channel suitable for the purpose, according to the

present state of the river, and for which 1 propose that three chains wide should be first purchased, the whole distance being, including Kelly’s ditch, about 14(J chains ; and to excavate a channel along the centre half a chain wide, and 4 feet deep, half the dirt from which to be v placod on each side, and forming banks on the outside of the above three chains, and the banks to be thickly sown with grass ; and also to add two spans of 30 feet each to the bridge already built over, Kelly’s ditch being 30 feet span, making the bridge 90 feet over all. The whole of which, including a portion of the materials for carrying out the work, would cost £3OOO. This plan, although it may be considered on a large scale, may, in my opinion, prove insufficient very shortly ; whilst the head of the Opawa would be still left open, with its enormously increasing quantity of water coming down as each Hood tends to widen the Breach ; therefore I would suggest that any outlay upon the above river should be applied at once to the head of it, as anything done lower down would be a fruitless expenditure. With regard to the plan of a dam for turning the river, some has proposed a weir dam, but neither this or any other dam (in my opinion) would answer, that would admit of any water passing over it, although a platform for its reception may be placed on the lower side, and which may answer for some time, I am decidedly of opinion it would not be for long, when it would wash a hole that would cause the whole of the dam to be washed away, as there is nothing but shingle to deal with all over the place ; it requires a suitable dam accordingly. The dam I would suggest the most suitable, in my opinion, for the place is a dam of sheetpiling, which could be driven to any depth required, and to be of sufficient height so as to admit of no water to pass over it, and to be carried out on the banks at both ends for a good distance, so as that no water from above, over the banks, would interfere with it; and the dam should be placed some 14 or 15 chains at least below the head of the Opawa, and below one of the falls in the lowest part of the river, as this would have the greater tendency to resist the force of the water working its way under the dam. It may also have the effect, I have no doubt, of raising a shingle bank between the dam and the Wairau river, across the head of the Opawa, and such a dam, if properly constructed, would not fail in stopping it effectually, and, according to an estimate I have recently made out, would cost £7,200; and as the water would require to be turned down the Wairau river, and kept to that during the operation of the works, I presume it would take about £B,OOO to complete the whole. This may be considered a large sum to be expended on it, but considering the great amount costly work to be performed, and the benefit to be derived fram it, together with the certsinty of its answering the desired object, it would very shortly repay the outlay, and moreover it would be the means of saving any (expenditure on the river lower down, and which would also tend to the protection of both -roads and bridges, and afford free communication with both town and country, as well as allowing the farmers and others to go on with their work again as before. With regard to the means of raising funds for the above object, I do not consider it my place to state, but leave that to all who are interested ; but this I would suggest, that the chonnels leading into the Wairau river be kept open in the meantime, until such time as the dam would be completed ; and those channels might be assisted by wings of strong manuka wattling, to be placed in convenient or suitable places higher up the Wairau river, where it may run close to the South bank, and which may cause a large portion of the water to go down the Wairau river, if properly carried out, and would no doubt relieve the Opawa by attention being paid to it after each flood. Apologising for trespassing so much on your valuable space,—l am &c., John O’Sullivan, Sen. Picton Road, July 9th, 1868.