FLOOD CONTROL

Manawatu Standard, Volume L, Issue 86, 8 March 1930, Page 2

FLOOD CONTROL

MANAWATU-OROUA RIVERS. MODIFIED SCHEME APPROVED. With the object of securing immunity from flood damage and improving the drainage, the Manawatu-Oroua River Board, since its inception eight years ago, has made exhaustive investigations into the _ best scheme for tho control of the two rivers. The cost of tho original scheme adopted was £450,000. Tho principal provisions were rectifying tho alignment of tho _ existing courses of tho rivers and increasing their carrying capacity by tho erection of levees. Tho diversion of tho Manawatu River, to shorten its courso to tho sea by 20 miles, was also considered. The tremendous cost of this project made it necessary for the board to procuro an estimate for a modified scheme. At Thursday’s meeting of the board it was resolved that these modified proposals be placed before the ratepayers for their approval after the land in tho board’s area had been reclassiged. Tho detailed report propared by the board’s engineer, Mr F. C. Hay, reads as follows:—“As instructed by tho board I havo made investigations into tho matter of modifying the comprehensive scheme of flood control for tho Manawatu and Oroua Rivers, with tho object of enabling the board to consider tho advisibality of doing tho work in stages. Tho principles on which I havo gone aro as follow: (1) Each section of tho work is part of tho comprehensive scheme; (2) tho work proposed is that which will give tho best results for minimum expenditure; (3) each portion of the river board district will receive benefit; (4) channel improvement takes precedence over banking. I now submit to you the particulars of 18 different jobs:— LOWER SECTION OF MANAWATU “Job I.—Rush Flat navigablo channel: This channel is 50 ft. wide by 12 ft. deep and is 57 chains long. The quantity of excavation is 100,000 cubic yards. The work can bo done either by a dipper dredge, by a suction dredge or by a land oxcavator working on a platform. It will cost £SOOO. The purposes of this work are (1) primarily to give a better route for shipping to Foxton and to obviate any objection from the Marino Department to the dumping of spoil from job 2 into tho channel of tho river;; and (2) secondarily to assist in the scouring out 'of the new channels proposed through Manawatu-ICuku and Moutoa. By tho adoption of certain methods for tho carrying out of job 2, the first necessity for the navigablo channel through Rush Flat may bo oviated; tho secondary object of tho channel, viz., to assist in tho scouring out of the new channels proposed above it, is not of sufficient present importance to justify this work. “Job 2.—Mankuk cut: This cut is 56 chains long and 40 ft. wide by 35ft deep. Tho side slopes would havo to be 1£ to 1 and the total quantity of excavation is 450,000 cubic yards. The work can bo done by a suction dredgo and would cost £20,000. This amount ’ allows for any compensation that might have to bo paid for severance of tho nativo land through which the cut is made. This cut joins the Manawatu River on tho west opposite Rush Flat and on the cast at a point half a milo north of tho outlet of the Moutoa main drain, cutting off threo miles 60 chains of the river. Its purpose is to tako flood waters from the Moutoa quickly -and to enable tho Moutoa main cut to scour out. The work can be dono by land excavators and at no greater cost than if dono by suction dredge, and if laud machines aro used there would be no necessity to use tho channel of the river for tho dumping of spoil and tho necessity for the Rush Flat cut for navigation would be obviated. “Job 3.—Main cut: This cut runs from tho Manawatu near Poplar mill, through tho Moutoa, and joins tho Manawatu again about It, miles above the Foxton wharf. It is six miles 41 chains long and cuts off 22 miles 20 chains of river. Tho work proposed consists of building stop banks an average height of 12ft 3in, spaced 22 chains apart centre to centre, cutting a central channel from tho Manawatu River at the lower end of the Karikari drain, a distance of five miles, tho building of two low level bridges, the construction of 11 floodgates and adjustment of Moutoa drainage, fencing both sides, protective work and planting, and included in tho estimate is tho purchase of 1225 acres of land. The following aro tho details of tho, estimate: Whirokino Road-river, 99 acres at £3O, £2970; Whirokino Road-Karikari, 238 acres at £6O, £14,280; Shannon Road-river, 56 acres at £7O, 3920; total, 1225 acres at £3B, £46,130.

“Bridges: Low lovol bridge whore contral channel crosses main road —Two 40ft. spans on ironbark pile piers, 20ft. roadway, with approaches, £1000; access bridge whore central channel crosses Langley’s Road —One 40ft span on piles, 9ft. roadway, £350; total, £1350. “Floodgates: Ivarikari, right, ono 3ft. x 60ft. Armoc, £200; Karikari left, two 6ft x sft. reinforced concrete, £1000; I.angloy’s right, one 3ft x 60ft. Armco, £200; Langley’s, right,, two 3ft. x 60 ft. Armco, £400; sm. 60, right, ono 3ft. x 60ft. Armco, £200; sm. 57 left, two 3ft. 60 Armco, £400; right one 3ift. 60 Armco, £200; 4m. 60, left, two 3ft. x 60ft. Armco £400; 4m. 35, right, one 3ft. x 60ft. Armco, £200; 4m. 20, left, two 3ft. x. 60ft. Armco, £400; 3m. 20, right, threo 3ft. x 60ft. Armco, £6OO. Inlet and outlet ditches and adjustment of outside drainage, £IBOO. Total, £6OOO. “Fencing: Thirteen miles at £1 15s per chain, £1820; contingencies, £180; total, £2OOO. Protective planting: Thirteen miles by 100 feet —156 acres —at £lO, £1560; contingencies, £140; total, £I7OO. Contral channel: Fivo miles by 40ft. wide by Bft. deep—--313,000 cubic yards—at Is, £15,650. Stop banks: Six miles 41 chains, average height 12ft. 3in.. 6ft. top, 2 to 1 sido slopes—l,llo,000 cubic yards—all Is, £55,500. SUMMARY OF ESTIMATE. £ Land (1225 acres) 46,130 Bridges, low level main road and access ... ... 1,350 Floodgates and drainage 6,000 Fencing 2,000 Protective planting 1,700 Earthworks 71,150 Total 128,330 Say £130,000

“Tho quantities have been taken out on the assumption that the stop banks are built separately and not by suction dredge from the central channel. This gives the least yardage, but it is not quite certain that tho work could be done in this way, which depends on whether land excavators supported on platforms could work, in the Moutoa. If so, a dipper dredge would excavate the central channel and draglines build the stop banks. If it were necessary to use a suction dredge, the stop banks as far as the Karikari would be built from the material excavated by the suction dredge out of the central channel. The quantities would, however, be increased as the slopes of the stop banks would have to bo made 3 to 1 instead of 2 to 1, and the total quantities of earthworks would be 1,520,000 cubic yards, or about 100,000 cubic yards more than if the work were done by land machines. Excopt for tho risk of having to write off the whole cost of tho suction dredge plant, this plant would be the more satisfactory. During the construction of the central channel the water for flotation would have to be let into tho channel through temporary gates on the bank of the river and bo controlled so that there would be no interference with the present drainage of Moutoa. “As regards the bridge, it will be no-iced that the present proposal is for a low level bridge on tho main road over the central channel. This is all that the River Board could be expected to do and, though traffic would still be blocked during flood time, the flood waters would run olf quicker and in that respect the users of the road would benefit. “As regards the bridge, it will be noticed central channel up to the Karikari would very considerably improve tho drainage of Moutoa. Tho bottom of the channel where it would connect with the Karikari would be 6ft lower than the present bottom of the Karikari drain, and at least 4ft. better drainage would bo available. Langley’s north and south and the diagonal would benefit in the same degree and, by taking advantage of tho floodgates proposed under this scheme, tho land lying between the river and tho cut below tho diagonal would bo very much improved as regards drainage. “This job is essential for the flood pro-

tection of the district. By doing it alone, Moutoa, Koputaroa and Makerua would receive immediate benefit, while Kairanga and Oroua would be able to get rid of flood waters more quickly even if no further work were done. “It will bo noticed that the central channel is in tho estimates only considered as being taken as far as the Karikari. The reasons for this are first, to obviate the necessity of putting a bridge on the Shannon Road and, second, to prevent too great a scour taking place, with risk of silting up the lower portion of tho main cut. “Another feature of this proposal which I wish to bring beforo your notice is that it connects with the Manawatu on the Foxton side of Poplar mill and that the stop bank on tho east side of the cut bends round to join the existing stop banks at the back of Newth’s. Several reasons govern this; the first is that if no further work were done upstream, this position for tho beginning of tho overflow is the best and cheapest for tho concentration of tho flood waters and tho consequent relief of the channel Lower down; the second is that ]t enables the Opui channel (job 4) to be located where it will cause the least disturbance of vested interests; and the third is that the section of river tapped by the cut as shown is at present in a better state for development than the section below Poplar mill which it was originally proposed to use. “Job 4. —Opui spillway: This work is to provide a flood spillway from Opui bend to tho Manawatu river - just above Poplar mill. It is 50 chains long and cuts off three miles 60 chains of river. It is not proposed to make this a cut at present; it would not be safe to do so till tho main cut was sufficiently developed. The following aro the details of the estimate: Land (103 acres at £7O), £7560; earthworks (100,000 cubic yards at Is), £5000; fencing (100 chains at £1 15s), £175; protective planting (15 acres ut £10), £150; floodgates, £400; spillway and contingencies, £1715; total, £15,000. This job is of direct benefit to Makerua and less directly of benefit to Kairanga and Oroua subdivisions.

“Job 5. —Tributary channel: This channel is for the purpose of taking ultimately the drainage from Makerua and Koputaroa subdivisions and the waters of the Tokonrnru, Mangore and Koputaroa rivers. Its immediate purpose is to relieve tho flow in tho main river below Paiaka and to act as a scouring agent on the lower portion of the main cut. The estimate for the work is as follows: Land (79 acres at £3O), £2370; earthworks (200,000 cubic yards at Is), £10,000; fencing (226 chains at £1 15s), £400; protective planting (23 acres at £10), £230; floodgate (two 3ft. x 60ft.), £400; contingencies, £1600; total, £15,000. It would not be necessary to cut a central channel at once, but merely to build stopbanks and lower the river bank so that small freshes would come down the tributary channel. But if land excavators were unable to work to advantage, tho work could be done by 6uction dredge and tho central channel cut at once. If this were done, however, more yardage would have to be excavated and an access bridge built, and the estimate would be increased to £IB,OOO. “Job 6. —Stop-banking Manawatu river from mouth of cut to Foxton, a distance of 70 chains, would take about 14,000 cubic yards, which at Is 3d per cubic yard would cost in round figures £9OO. This work is necessitated because of tho raising of the water level at the mouth of tho main cut, which will happen till tho Man-Kuk is scoured out. “Job 7.—Stop-banking the right end of the Manawatu from the end of the main cut upstream to Conolly’s camp: This work is required in any ense for the protection of Moutoa from small floods and will take up 48,000 cubic yards of material, oosting, at Is 3d per cubic yard, £3OOO. “Job 8. —Deepening Koputaroa stream and stop-banking: This work, which will be of benefit to Koputaroa subdivision, will cost about £3OOO. “Job 9. —Cutting off bend in Manawatu liver opposite the Koputaroa river. Tho length of cut is eight chains and will cost £2OO. The land severed by tho cut is 36 acres, which at £25 per aero will cost £9OO, making the total estimate £llOO. Principal benefit to Koputaroa, but has some interest to Makerua. “Job 10. —Cutting off double bend in Manawatu near Moutoa hall: The total length of cuts is 30 chains, while about 17 chains of stop bank on the Makerua side will have to be re-erected. The total yardage is 20,000, which at Is 3d will cost £1250. On tho Moutoa side 31 acres of land will be severed, with 10 acres on the Makorua side. Land (31 acres at £35), £1035; 10 acres at £SO, £500; earthworks (20,000 cubic yards at Is 3d), £1250; contingencies, £165; total, £3OOO. Benefiting Makerua and Mputoa subdivisions. “Jobs 1 to 10 comprise the work in the lower section of the Manawatu and the total estimated cost is £196,000.

UPPER SECTION OF MANAWATU. “Job 11.— This works consists in cutting a channel across tho narrow neck of land at Paki’s Point; 92 acres of land would be severed, and the estimate for the purchase of land and cutting the channel is: Land (92 acres at £3O), £2760; cut (15 chains at £29), £440; total, £3200. “Job 12. —This work is the cutting across the narrow neck of land at Page’s Point, above Miss Edwards’s farm, and the estimate is: Land severed (48 acres at £3O), £1440; cut (three chains), £160; total, £I6OO. “Job 13. —This work consists in the construction of a stop bank about 3ft. high round the bight in the river at the end and north of the Tiakitahuna road, taking about 4000 cubic yards, and the estimate at Is 6d per cubic yard, allowing for contingencies, is £3OO. “These three jobs would be of direct benefit to Kairanga and their total cost is £SIOO. OROUA RIVER. “Job 14.—This cut is for the purposo of diverting the Oroua river from the bend below the Rangiotu bridge into tho Manawatu river below Russell’s house, about 16 chains below the outlet of Burke’s drain. It is 30 chains long and cuts otf two miles 16 chains of the Oroua river. The estimate is as follows: Land (18 acres at £SO), £900; earthworks (20,000 cubic yards at Is 3d), £1250; floodgate (threo 3ft. Armcos at £166), £500; access bridge (four 40ft x 10ft), £1550; total, £4200. Benefiting Oroua and Kairanga subdivisions. “Job 15. —Tho course of the Oroua is particularly tortuous over a length of one mile situated some distance above Mangawhatu. This job conisst in straightening the river and reducing its length from one mile to 40 chains. The estimate does not provide for the purchase of land, as the land affected is entirely between stop banks and the various severances would counterbalance each other, so that little land, if any, would be taken off the titles. The total length of the various cuts would be 36 chains and the cost of doing the work, allowing for clearing, would bo £750, benefiting Kairanga and Oroua. “Job 16.—This work is an alternative to job 14, but would not be of such great benefit. It consists in stop-banking the Oroua on the left 6ido from Rangiotu to the junction with tho Manawatu. About 20,000 cubic yards of earthworks would be necessary, which at Is per cubic yard, and allowing £2OO for snagging, would amount to £I2OO. Benefiting Lower Kairanga. “Job 17. —This work is the erection of stop banks from Rangiotu to above Mangawhata and joins up with job 15. The total quantity of earthworks is 60,000 cubic yards, which at Is will cost £3OOO. Benefiting Oroua and Kairanga. “Job 18. —This work is the construction of a floodgate at tho mouth of the main drain of the Sluggish River Board’s district. The structure would be of reinforced concrete with ironbark gates hung vertically and giving a clear opening of 120 square feet. It is estimated to cost £I2OO, with provision for an access road over the top. Benefit to Oroua subdivision. “These four jobs, Nos. 14 and 16 being considered as alternatives, total £9150 if No. 14 is undertaken, or £6150 if No. 16 is done instead of No. 14. They directly benefit tho Kairanga and Oroua subdivisions. “Omitting jobs 1 and 16, the total cost is £205,250, made up as follows: —Land, £66,925; earthworks, £121,970; bridges, £2900; floodgates and drainage, £8800; fencing, £2575; planting protective belts, £2OBO. “The total area of land to bo bought is 1759 acres, and the total ynrdago in 6top banks and cuts is 2,410,400.”