BATTLE OF STOPBANKS

Chronicle (Levin), 18 June 1947, Page 3

BATTLE OF STOPBANKS

ENGINEERS' REI'ORT TO BOAItD The battle of the stopbaiiks aloug the two sides of'the Manawatu River in, tht? lower reat^ies should come to au eua following a joint report to the- Manawatu Catchment Board yesterday , by the engineera to the Manawatu-Oroua River Board, Mr. H. R. Farquhar, .the Makerua Drainage Board, Mr. O. J. Dolan, the Manawatu Oatchinent Board, Mr. P. Gr. Evaus, and the resident eugin eer of the Works Departme'ut, Mr. A. R. Acheson. Mr. y. W. Barber, of Moutoa, moved the adoption of the report, aud it was Seconded by Mr. J. D. Aitchison, o± Makerua. The motiou was unaniinously carried, whereupou the represeutatives of the opposiug areas, Messrs Barber and Aitchison, warmly shook hands. Tlie' report of the engineers, togetlier with their reconimendatiolis, was as follows: — . Plans which had been prepared from levels by the catchment board were studied, and it was agreed tliat the levels as shown represented tlie position at the present date. Tliey sliowed the levels of the Makerua and Moutoa banks from about 2 miles above Shan n,on bridge to about (5 miles above the bridge, i.e., from Bryant's to Wail's spillways and the level of the east banli of the Tokomaru Stream i'rom its junetibn with the Manawatu to 5 miles above this point: From the plans, the following points arose. Below Shannon bridge both the Moutoa and Makerua banks were slightly above master grade, except for a few Tow points on both banks. Above Shan flon bridge, a line had been drawn ou the same gradhsiit as master grade for ref'erence, and the Moutoa bank for some considerable lengtlis was beiow this. For oue short length 4A miles above the bridge it was 4ft (iiii beiow this line and for lengths at Am, lim and 4|m, some lxt to 18in below it. The Makerua 'bank was above this line rising at the upper end near Wall's spillway to about 2ft tiin above it. The Makerua bank was at present about 3ft above the Moutoa in the length from 1 mile above Shannon bridge to WallV spillway. 5 The plans of the Tokomaru stream showed that this bank was for considerable lengths beiow the level of 28.00 whieh was the agreed level for master grade at Shannon .bridge, the lowesl portions being about 2 feet, and over .1 mile was nearly 1 foot below this level. it was agreed, altliough plans Were not available, that the Mangaore banks in the Makerua area were, at some points, .alsa below -mastqr grade, taken. ajt, tlie junction of the stream and river. Also it was noted that the Moutoa banks, particulars above Shannon bridge, were in most parts smaller in cross-section than the Makerua banks. There was not at present snfficient inforui'ation : :aivailable tb . give • f complete calciiiations bf the capacity of the Manhwatu River, but from existing planS, the following approximate results of chleulations by the catchment board engineer were aceepted as giving a guide to eonditions. At present the river banks would be over-topped when a sustained llood of about 13ft Gin at Fitzherbert. gauge was experieneed. The river in the length from Wail's to the lower Moutoa would be capable of earrying with the banks raised to the gradient shown on the plan and witli no spills about 52,(JU0 eusocs. With the provision of spilhvays, the flow would be inereased due to the increased gradient in the water surface induced by the lowering of the level at the spills, and if there was one spill of 20 ehains provided every 3 miles, the flow would be in tlie neiglibourhood of 58,000 cusecs. This was about equal to a 15ft level at Fitzherbert" bridge. This gave an increase of about (5000 cusecs. With the banks as recommended, it would cairy about 48,000 cusecs or approximately 14ft on the Fitzherbert gauge. The banks in the lower Moutoa area had been raised very consideriibly of recent years, and in spite of the provision of spilhvays, tlius must have in creased flood level considerably in the river. The approximate calculations showed that the capacity of the river, even with bank levels raised and spillways provided, was not adequate for maximum floods. It was essential if full protection was to be givcn from floods, to have a comprehensive scheme probably with some form of bypass as proposed in previous investigations. Due to the raising of banks in recent years, the flood level had been raised in the area near Shannon bridge and now for a sustained 14ft flood on the gauge at Fitzherbert, there was danger to all banks in the lower Manawatu area. This danger was most acute in the upper Moutoa area and the Tokomaru and Mangaore stream areas.

■In view of the grave danger now existing, it is considered that banks should not be raised except in exeeptional circumstances, until a complete comprehensive scheme has been prepared," stated the report. In consideration of the particular problem at Barber 's Spillway, it was noted that the Main Highway Board would not look with favour on the provision of an extra area where the road was liable to flooding. In. addition the settlers between Wall's and the proposed Barber 's spillway would be cut of? in flood times. It was noted also that consideration in flxing the height of banks must be given to. the effeet of afflux or inm-eased heights of the water at sharp bends. The effeet of providing a spill at Barber 's together with the raising of the banks in the area, would give very. little additional safety to the upper Moutoa area and would raise the j flood level in this area, with eonsequent risks to Tokomaru banks. Tho following rccommonclations wero

inade:— 1. Bank levels must not be raised further in the lower Moutoa area except where prior permission of the catchment board is given in special circumstances. 2. Bank levels in the upper Moutoa area, i.e., between Shannon bridge and YVall's spillway, should not be raised excGpt that the extremely low parts tnay be raised to tho level 1 foot below the gradient line shown on the plans. 3. The banks in the upper- Moutoa area may be widened and cross-seetion improved 30 that they will not be breached so readily in the event of overtopping. - 4. The Makerua Drainage Board should omuder the raising of the banks on the Tokomaru and Mangaore streams in tlie iow areas at an early date. 5. Until the provision of complete protection has been carried out, the upper Moutoa settlers should have special consideration for assistance in the event of flood darnage.