FLOOD CONTROL.
(Concluded from Page 1) TUESDAY’S SITTING.
The first witness heard was Mr Hugh Akers, who said that he was the owner of considerable land in the Makerua district of which he had had a lengthy experience. The 1002 flood had oveitopped the natural banks, but subsequently floods had come over the lower portions of the banks. He had recently built a house in the district and a bank he had erected was the only insurance he had against flooding. He was not engaged in dairying, but fattened stock. He thought that part ot his property was among the best fattenino- land in New Zealand and it would improve when the banking and drainage were completed. It paid him better to grow grass than to plant lucerne. In his opinion, the banking of the Makerua swamp had improved the flax which, before the work had been done, was frequently under water for a week at a time. the Makerua Board had “banked” as the floods were bringing in weeds and, without protection from floods, it was impossible to keep weeds out. Goat’s rue was a dangerous weed as it “blew” stock turned on to it. In 1898 property fringing the Makerua swamp was sold at £7 or £8 per acie. His property was fairly high. There were some settlers paying over £1 per acre rates, plus the county rate. The average would be about 14s per acre. Mr Baldwin: Would you as a settler welcome the cut in the Manawatu river as an insurance to. your properly ? . Witness: Certainly, I would. Continuing, witness said that he had done a fair amount of protection work as he had suffered some of the worst erosion to his banks. The river had obtained a considerable hold before lie had attacked the situation. Describing the method of dealing with the trouble he said that he sunk blocks on wire ropes into.the water and piled in logs and trees. When silt had collected he planted willows. This had been successful. He preferred a quarter mile channel as it would be more economical. Cross-examined by Mr J. P. Innes, witness said that he doubted whether some of the settlers could stand further rating. Some were paying about 2os per acre. He was unable to say exactly what the rate was, but it was fairly high. He knew that the amount borrowed by his board was very near the maximum allowed. If the proposed cut had been put in before the Makerua Board had commenced its work, the rates would not have been so high. To Mr Cooke, witness stated that he had not taken into account special rates. He did not think that the maintenance rates would be as high as some people expected. Mr Hay, he thought, had been very cautious and was on the safe side. Ete knew that the Borough Council and the Palmerston North River Board had -spent some £30,000 in protecting the river bank just opposite Palmerston North. He did not favour rating Palmerston North for the board’s scheme. If the scheme were put into operation, it would mean that the board would have to maintain a considerable portion of the Makerua bank. PROGRESS OF TOWN. Mr H. L. Young, chairman of the Palmerston North Chamber of Commerce, next gave evidence. In his opinion the increase in the business done by Palmerston North with the surrounding district in the last ten years was substantial. One firm had informed him that up to 40 per cent, of the Saturday business came from the country. About 20 per cent, was an average. The facilities for traffic had had a beneficial effect on the town as had also the increasing population ot the country districts. To Mr Cooke, witness said that it would be impossible to calculate what benefit would accrue to Palmerston North through the proposed flood control scheme. In 20 years to his knowledge the road to Foxton had been blocked on three occasions for about a week or 10 days at a time.
To Mr Baldwin: He thought that, provided, say, 1800 more families settled in the district as a result of the scheme. Palmerston North would benefit considerably. Mr A. Seifert, who was unable to be present in the morning, was called to give further evidence. To Mr P. E. Baldwin, witness said that lie knew the lower part of the Mputioa district and in his opinion there were considerable areas or lowlying land which could be acquired by the Government and which would obviate to a large extent the compensation question arising out of the board’s scheme. He was convinced that the scheme was sound from an economic viewpoint. He did not think the district could stand the burden of £450,000, as there had been well over £IOO,000 spent by the Makerua Board. Forty-three and a-half per cent, of the whole of the betterment of the scheme, according to Mr Hay’s report, would fall upon the Makerua. After giving credit for what had been spent by the Makerua Board, the Manawatu-Oroua Board would charge them £254,000 or about £l2 per acre. This at seven per cent, would amount* to about 16s per acre. In the case of his company’s property it would amount to more, probably £1 per acre. Provided no credit was given for work already done, that amount would be in addition to the rates already being paid. He did not think the land could stand it. He stated that, in the flax area, the roots of the crops were included in the unimproved value for taxation pur|>oses and for local rating purposes the leaf was included as part of the unimproved value. The industry was thus handicapped. Witness stated that the land in the Makerua district could not stand much more rating. The relief to the banks would be welcomed, but too much could be paid for a good thing, band adjoining the flooded area would benefit were the scheme gone on with, as would also the neighbouring towns. The counties would benefit from the increased rating values. The towns, Palmerston North for instance, would benefit as floods reduced considerably the spending power of the farmers. MAKERUA RATING. Cross-examined by Mr limes, witness said he was satisfied that the Makerua land could not stand very much more rating. Mr Innes: Assuming that tho scheme went on, and the Manawatu-Oroua Board did not take over the Makerua banks, then you would be liable to pay the ordinary rate struck by the board? Witness:’Well, that,would hardly be a fair deal. " To Mr Cooke, witness said that in his opinion, if the River Board had to raise £175,000, Makerua should be om’tted. Mr Cooke: Now don’t you think the same should apply to the Palmerston North Borough Council, as that body has spent a considerable sum in pro teeting the river .banks? Witness: It would be perfectly logical to credit them with any effect ve work. Mr Cooke then asked whether, m the Sacramento (U.S.A.) Valley, the banks were protected, but witness said that, although he had not seen any, he had not asked about the matter, as his visit there was to the lower regions where erosion was not serious. Possibly, in the higher regions, the danger might have been greater. In reply to Mr Baldwin, witness said that in onlv two cases in the Makerua district hacl the banks been damaged, and that was where the banks had been too close to the river. He was sure that the travelling public had * been benefited considerably by the operations of the Makerua Board. At this stage Mr Baldwin stated that, with the exception of certain statistical evidence and that of the engineer of the Manawatu-Oroua Power Board, that was the ease for the River Board.
ENGINEERING EVIDENCE. Mr Innes then called upon Mr 11. W. Holmes, civil engineer, of Wellington, who said that he was familiar with the country under discussion. Some slight confusion had arisen in the use of the term “bank,” said witness, who added that he proposed to use the term to describe the river bank, and to use the term stop-bank to describe the banks to be erected. He then described the composition of the old delta which Makerua was situated on. It was composed of sea-borne sand and river-borne silt. The lower part of the Manawatu river could be compared with the delta at the Clutha river, where considerable trouble had been experienced. Witness also called attention to the loop in the river adjacent to the town of Foxton. This be said, could never carry the total flood water of the river. Witness then described by means of a map how a scheme which had been, ■onsidered in 1907 proposed to divert the river. Reverting/ to the question of velocity, witness said it was generally conceded that, in light sandy country, a velocity of less than one foot per second would cause erosion on the bottom and banks. That would he the velocity of the water on the bed ol the river. The mean velocity of the water in the channel would be about three feet per second and the surface velocity about four feet. At a velocity of five feet per second, the banks of the river would need permanent protection. Proceeding, Mr Holmes dealt with water-races in connection with mining, stating that, when the velocity of the water reached 2.5 feet, it became necessarv to use rock owing to erosion. Measuring eleven miles up the present channel of the Manawatu river -from the sea, the bed of the river was five feet below the level of spring tide low water at 'the sea. After passing the 11 mile point the bed was five feet above low water spring tide. ihe rivor was tidal as far as Moutoa and salt water actually passed some considerable distance beyond Foxton. When the new cut was made there was every reason to suppose that the present' tidal conditions would obtain in tho new channel, and that the salt water would flow up for half tho distance of the cut. The consequence of the different levels in the river would be similar to what had happened in every other river he was acquainted with. When the course was shortened, or the velocity increased, either one or two things happened—the river lowered its bed by cutting back or by developing sufficient “meanders bv means of erosion to make up for the loss of length. Witness amplified Ins remarks by saying that it would be the same as if tho whole country had been lifted up from 10 to 20 feet and a water-fall thus made at the mouth of the river. Such a water-fall would easily cut back through the easily eroded material. There would then be seen raised river terraces such as occurred in many places in the Rangitikei valley and between Ashhurst and Palmerston North. It was proposed in the scliemo to prevent the new “meanders” forming by means of stop-banks and, therefore, the only course for tho river to adopt would be to cut back or lower its bed. Tho consequence of this cutting back would be an extremely difficult matter to combat, and would extend upstream in the Manawatu as far as the Gorge and also in the Pohangina river. This condition would prevail until tho natural slope of the river bed was restored. “ONLY PRACTICAL SCHEME.” Reverting again to the part of the river between Tiakitahuna and Burke’s drain, witness said that the maximum velocity of the current would occur when the river channel proper was full to the brim and it commenced to spill over. The reason for this was that, when the water flowed over, it met itself flowing in the opposite direction as it were owing to the bends in the channel. Thus there were two surfaces of water flowing against each other at this stage which now caused retardation and consequently loss of velocity. Witness therefore assume*! that the maximum shingle travel occurred just before the overflow. He ijssumed that work on the new scheme would be commenced by cutting through the two loops near Foxton and leaving a small portion in place. When these and the bank at Moutoa were cut the result would lie a sudden drop in a short distance with increased velocity upstream. A mass of material would then be carried down and temporarily deposited in the now cue. Witness stated that lie thought Mr Hay’s scheme was the only practical one* but that gentleman considered that certain costs should be considered as maintenance. In the case of the Manawatu river it was impossible to carry out permanent protection in the first instance. It was proposed to carry out the work by means ot a pilot channel of large enough dimensions to provide enough material for the formation of stop-banks. The scouring action of the water was being relied on to enlarge as the river “meandered,” and steps were to be taken to prevent the destructive action by means of protective devices. The provision of such protection was a matter of«considerable difficulty. In the lower portion of the river, salt water was present and ordinary vegetation would not live near it, while timber protection would be liable to destructive pests, particularly the teredo. In the United States of America, particularly in the Mississippi district, and in Japan, it had been found necessary to adopt permanent protective devices uonsisting of concrete slabs on wires. The river banks were sloped to receive the slabs. The slabs formed a surface which to a great extent were mobile and adapted itself to inequalities existing originally, or formed subsequently by erosion. Witness stated that Mr Hay had allowed two per cent, of the capital cost for maintenance purposes. Two per cent, of £450,000 amounted to £9OOO. The protection required would be necessary only along the concave sides of the* bends—or, ,as they would be, embryo bends. ■ Witness estimated the cost of the work to be about £ISO,(XX) to £200,000. The expenditure would be spread over a number of years, say, 20. Nine thousand pounds for 20 years amounted to £IBO,OOO which confirmed liis estimate. In his opinion the ratepayers should realise at the present the total expenditure necessary to provide a permanent channel. When this had been done the maintenance would probably vanish, or nearly so, as the river would have assumed a permanent and stable condition. Referring to the probable effect of the cutting-back of the bed of the river, witness said that it would lower the flood level at Burke’s drain and would also affect the. railway bridge at Longburn. It was logical that the board should take over the control of the river right back to the Gorge. ARTIFICIAL LAKES.
The modeni method of flood control was by the formation of artificial lakes. The Government was assisting in a modest way by the construction of the dams at Mangahao. In his opinion the board would be well advised to spend a few hundreds in research work. He himself had obtained very satisfactory results by constructing models of the country to be de,alt with. The Foxton bar and estuary were situated on a sandy coast and were not in any way controlled. The natural forces at work were the flood waters, the tidal currents and the action of the sea. The effect of the flood water was of a very temporary nature. There was no doubt there was a slight deepening of the river due to a flood, but the general effect was to widen the mouth of the river to a, sufficient .width to enable the water to jie discharged. As soon as a north-west sea drove in it would narrow the mouth again and in a few hours’ time- would undo the work of the flood. There had been a suggestion made to the effect that the wharf there should -be shifted to the estuary, but that was useless as there was no knowing when it would be yards away from the water, owing to the action of wind and sea.
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Manawatu Herald, Volume XLVIII, Issue 3541, 23 September 1926, Page 4
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2,687FLOOD CONTROL. Manawatu Herald, Volume XLVIII, Issue 3541, 23 September 1926, Page 4
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