CONTROLLING THE MANAWATU RIVER.

Manawatu Standard, Volume XLI, Issue 9743, 7 March 1914, Page 5

CONTROLLING THE MANAWATU RIVER.

WHAT THE RIVER BOARD INTENDS DOING. A TESTED SCHEME. Shortly after its formation the Palmerston North-Kairanga River Board engaged Mr E. E. Fisher, the Board's present engineer, but who was then ergineer of the Hutt River Board, to inspect the Manawatu river and report on the regulation and control of same. This Mr Fisher did, taking four davs t) make an exhaustive examination oi the river within' the board's district. On his rounds of inspection he met and interviewed some old settlers who afford«hl him valuable information relating ti the history and flood conditions of the

river for many years past up to tli « present time. It was only after having obtained a thorough knowledge of the situation on the ground that he proceeded to consider the subject in all its bearings and to frame his report and estimate. What Mr Fisher rejiorted to the board is given below, and gives a comprehensive idea of the undertaking the board has in hand. BANK PROTECTIVE WORKS FUTILE.

The first question, Mr Fisher states, that presented itself to him was:—ls'ii practicable with the present erratic course and congested state or the river channel to efficiently maintain any class of bank protective works that will pievent the erosion of land in places hereafter referred to? Mr Fisher considered it not feasible in practice to do so. This was amply demonstrated by the futility of such works in the past! notably at the Fitzroy street bond. Conclusive evidence of the futility of such works under similar conditions he had experienced in the Hutt river where ho had twelve years practical exigence of diffor wit classes of works undor varioiv conditions. The class of work in que*tion was employed in the Hutt river for several years, the capital and maintenance cost being very heavy. Even then i it was not a success. The diffic ultv was ' overcome in the Hutt river by means! of open timber groins which had tV effect of first relieving the weak points and nnally completing restoration bv reclamation. This, said Mr F>her/ has proved a practical and sarisiactorv remedy, being economical and offtM-rive THE ONLY EFFECTIVE REMEDY. The maximum discharging capacity of the Manawatu river is considerably greater than that of the Hutt river ami the maximum flood capacity about- three times that, of the latter* river Tho angles, however, are less accute, consequently the conditions of the Manawatu river are more favourable and Mr Fisher believes, would respond ' more readily to treatment for diversion than has been the case rith the Hutt river ) oltime and velocity are essential to facilitate the development of the river diversions through the agency of open groynes It is manifestly "evident says Mr Fisher, that the works employed to protect the banks in the Manawatu river bends has proved effective, and it is also manifest that it is hopehw to seek an effective remedy within the radius of the bends subject- to erosion because the specific gravity of the river U ,P the high convex banks of shingle creates an irresistible hydraulic action in the concave (opposite) "sections xf- l TlVOr Therefore, Mr t isher considered that the relaxation of the present restrictions of the river channel was the only practical solution ot affording efficient protection to the bends. FIVE YEARS TO COMPLETE. The next- question Mr Fisher considered was whether the river channel could be iegulated at a reasonable exjiendiUire to prevent further waste of land He considered that by the employment of a system of open timber groynes placed in suitable positions above" the respective l>ends affected, the banks would be first relieved of undue pressure and the erosive action minimised Then, by the agency of sufficient groynes, time, ard fWls, the river would be completely diverted from the respective bends and in time the bends would be fully reclaimed. The groynes would then have established a definite and permanent channel which would result in the augmentation of the velocity and discharge of the river and the reduction of the flood level. A complete and successful regulation of the river channel could only be achieved by adopting a comprehensive groyne 6<?heme. Mr Fi.siier estimates that with his scheme (given there are sufficient floods) the necessary diversions would be accomplished in about five yoars. LOCATION OF THE GROYNES. The groynes required would be f jft above summer level and about lL'nft in length. There are five points at which Mr Fisher considers the river should be diverted from its present- channel. (1) At Mr Anderson s property where, tor a start, three groynes would be necessary; (2) at Mr Mcßae's. where one groyne was wanted: <:">) at the Fitzroy bend, where three ought to be put in (4) at the Cliff hill, where three were necesasry on one side and one on the other: and (5) at the rubbish depot below the bridge, where three groyne* should be erected. It was absolutely necessary to start at Anderson's bend about 40 chains above the board's district. The groynes as above enumerated should bo erected if possible in one season, as co-operative action was necessary. The following season the scheme should be added to according to degree of development, and so on until the respective diversions have been completely effected. It is impossible to say accurately how many groynes will be required to complete the scheme, but approximately about 40. that is eight groynes for each diversion. There" is no maintenance required with this class of groyne, but it- is necessary to remove drift timber that will collect on them in times of flood. In conjunction with this groyne system it is necessary to plant with willow stakes an area of the reclamations as established from time to time by the groynes. Mr Fisher said he felt sure the diversion scheme as described is the correct thing for the control of this river providing it is systematically installed. He did not anticipate any difficulty in carrying it to a successful issue. The staff required for the construction of the groynes was four men. and these men could do the necessary willow planting as required. ESTIMATED COST. The estimated cost of the proposed works is as follows: £' First instalment 14 groynes 3360 Balance to complete scheme 6240 Contingencies and probable extensions 500 Willow planting 800 Plant for groyne construction ... 524 I Engineering and supervision 571 Total £11.995 The Permanent maintenance of works after completion would amount yearly to alnuit £SOO. IMPORTANT TO THE BOROUGH. To a Standard representative Mr Fisher stated that the proposed work;were of the greatest importance to tlx borough as a whole. He "pointed out in the firs! place that the septic tank. 1 were in immediate danger from tin rnor. At the old racecomse the watei was cut tin 2 m extT.s'Virly, and iherc were indications in the nks there c.f old river channel-?, one difl H know when a flood might sweeofML \Je away and the septic tank with " t,ieiv v :'^ the danger of the supply being

■ut off by the destruction of the bridge utd also tho big yearly loss of land at Fitzroy street. \\ lien tho diversion scheme was completed the river would )e confined practically to a straight 'oui>e from Stoney creek right down last tho old racecourse, and when the "iver was once in that straight channel t would bo easy to keep it there. The pressure on both banks would bo practically equal, and consequently it would have 110 tendency to curve.