WAIKATO FLOODING.

New Zealand Herald, Volume LXIII, Issue 19470, 28 October 1926, Page 11

WAIKATO FLOODING.

EFFECT ON DRAINED LAND. RIVER BOARD'S GROYNES. REQUEST MADE FOR REMOVAL. FORMER EXPERT CRITICISM. No. I. Th* request of the Aka Aka Drainage Board to the Government that the groynes in the Waikato River should be removed was inspired by the necessity for increasing the efficiency of drainage works, upon which the productivity of very fertile areas depends. The interests this one hoard represents are sufficiently extensive to call for prompt examination of the case submitted. In addition to these local interests there are others of more direct public importance involved in the vagaries of the lower river, which make it doubly important that whatever action is required to lower the water level and expedite the discharge of flood waters should be taken if it is within the bounds of financial possibility. The Present Position, While opinions are bound to vary as t« what ought to be done to help the river to be a better drain for the land and a more useful waterway, there probably will be general agreement upon the following points:— That the groyning established by the Waikato River Board, which no longer functions, but for the debts of which—some £IO,OOO or £12,000 —the ratepayers of the area will have to go on paying for 20 years or thereabouts, has not benefited tho marsh lands about Mercer, which was their purpose. That such lands as those of Aka Aka that, had been drained for. nearly a-quarter of a century are to-day more difficult to unwater than in the past. That during the past ten years flood waters have been held longer and that the effect, of floods extends nearer to the mouth of the river. That silting has occurred behind some of the groynes and that in some of the outlets from drained areas sand has been Aiposited and has thereby reduced the capacity of the channels. Contributory Causes. It is not suggested by those who desire the removal of the groynes that the growing flood and drainage troubles s.re attributable solely to the groynes. It is generally believed that the bed of the lower river has risen through the deposit of pumice and sand, which, owing to lack of current, is net taken to sea, btiq in regard to floods it is beyond question that the denuding of the watershed of bush and the draining of swamps has had ihe effect of allowing rain to reach the river more quickly than formerly, thus intensifying the difficulties of winter and spring and diminishing the normal flow of summer and autumn. Thus it is not simply a case of deciding whether a series of groynes is causing damage in its vicinity, but an involved problem demanding comprehensive attention by experts. At the same time, the immediate good of lands where drainage is now becoming impaired is the outstanding practical aim. History ol the Board. The history of the Waikato River Beard is not pleasant reading, and it clearly demonstrates that any work affectinj; a river should have official sanction. The preliminary steps took place in 1911. when a combination of landowners south of Mercer formed a drainage association with the object of reclaiming their marshes, which are so low that a moderate rise in the river caused them to be submerged. The possibility of the operations benefiting Crown swamp lands in the Whangamarino and Maramarua districts was acclaimed at the time. The jussoeiation succeeded in forming a river hoard, the proposed district of which was much larger than was ultimately defined. Unfortunately when the board set to work upon its groyning system downstream. the levels supplied to it were inaccurate and its assumption that notwithstanding the reduced fall which further investigations disclosed the scouring effect •would be sufficient to achieve the desired end was fallacious Condemned by Commission. The first official scrutiny of the board's operations was apparently that of the expert. commission of 1917, the members being Messrs. F. W. Furkert, C. B. Vickerman and W. C. Kensington. Its report was generally in agreement, with that of Mr. Ashley Hunter, C.E., already supplied to the Aka Aka Drainage Board. The commission, answering a list of questions in its order of reference, stated that the groynes were not necessary for the protection of the bsnks of the river. Although some groynes, if properly placed so as to provide a channel of sufficient width, should eventually tend to improve navigation, the structures as placed and built were not satisfactory. It, was explained that the groynes were more of the nature of training-walls, consisting of rows of white pine piles in some cases attached by wire and wattled in between with wilJow-. Some of these walls have now become willow banks. The groynes, continued the commission, ■were not necessary for the effective discharge of flood waters, but, rather from evidence had a retarding effect. Silting np had occurred at the back of the groynes and this silting, if the groynes were kept in repair, would extend downstream and eventually affect the mouths of the Aka Aka Drainage Board's drains. So tar the banks had not seriously affected tho egress of water from these drains, but it was merely a matter of time, and any interference with the drains must necessarily reflect adversely on the land. Substantial damage had n't occurred., but it was likely. It could be avoided, however, by constructing i new outlet sufficiently far down stream to l.e beyond the adverse influences or poss.bly by periodical dredging. The removal f the groynes would cause no damage to the river or to the land bordering if,. They had not improved navigation to any extent up to that time. Owing to the hard shoal at Pakau Stream, known locally as the "sheep-paddock," not having materially scoured, the expected action of the rest of the scheme had not, appra ciahly taken place.