FLOOD DAMAGE

Chronicle (Levin), 26 July 1947, Page 3

FLOOD DAMAGE

COMPREHENSIV E REPORT The most comprehensive report 011 flood damage ever presented before the Manawa tu-Oroua River Board was made by the engineer (Mr. H. R. Farquhar) at a meeting of the board last week. Mr. Farquhar's report read as follows: — "Preeipitation for 24 hours varying from 4in. at the southern to 2in. at the northern end of the upper Manawatu Catchment produced flood peak at the Fitzherbert gauge of 17ft. 3in. for seven hours on Sunday, June 29. The time in hours that the flood was above each foot mark commenced at 10ft. on the Fitzherbert gauge as follows: — 10ft., 44 hours; 11ft,, 39 hours; 12ft., 35 hours; 13ft., 32 hours; 14ft., 27 hours; 15ft., 21 hours; 16ft., 16 hours; 17ft., nine hours; 17ft., 3ins., seven hours. Makerua: For 12 days preceding the flood the level at Fitzherbert gauge aid not fall below 5ft. 6in. and there were six freslies of approximately 8ft. Floodgates in the lower river were mostly closed, so local water had to be retained. Thls eaused local flooding of several thousand acres of j the lowest land in Makerua and also Koputaroa for the week before the flood. i "Koputaroa: Mangaore stop- j bank was breached during Satur- 1 day night at the new Te Maire ; floodgate and when found the gap ! was too extensive to repair. This ! breach widened to 70 feet and to a , depth of 30 feet below the top of the stopbank, flooding the Buckley area and washing out- the Main Trunk railway. At the Koputaroa floodgate, the internal water ievel was one foot below the flood level in the river. The Koputaroa stopbanks were breached in several places on both sides of the stream, and the internal flood watei*s nioved over the Koputaroa subdivision towards the high land on Winiata's, where the Manawatu ; left stopbank ends, some two miles above the Whirokino Bridge. The i internal water level was 4ft to 5ft. 1 above river flood level, and the bank was blown to allow this internal flocd water to return to the river. j "Moutoa: Wall's spillway dis- ! charged for 26 hours generally 6in. | deep. All but heavy trafiic was j unable to use the road. Recom- ■; mended that the southern side of j the road, where the spillway waters pass, be cleared of tall grass and obstructions. This will materially lower the water level at the trafficway and reduce the time that cars ■ are held up. "Bryant's spillway discharged I slightly at the upstream end and commenced to seour. This was ' sandbagged after the peak to nre- 1 vent further scour. Flattening the land side slope still further is required a'nd encouraging the growth of a dense sward, as the material in the bank is very light and sandy. Spring's spillway dis- : charged for a few hours, three or : four inches in depth. Kari spill- I way juest discharged, while Paiaka-' spillway did not discharge, having . a margin of four to six inches. Harper's spillway had 15m. to 18in. margin. Flood level at Whirokino Bridge was 10ft. 9ins., one foot above the high spring tides a week j or so earlier. The amount of flood- ! water on Moutoa is exceptionally j small. The main results of this i flood are that the Taonui basin and Koputaroa sub-division have 1 been heavily flooded, Moutoa and | Oroua have been slightly flooded, I while Makerua without river water has had several thousand acres under water for a week or so. "The small discharge over Wsfll's spillway is mainly the result of the Whirokino Cut. The increased flood gradient in the lower river is causing degrading of the river bed progressively upstream, and so increasing the flood discharge of spillways below the Shannon Bridge, and probably a little to that of Wall's, but insuflicient to account for the marked reduction in what would normally be expected to pass over Wall's spillway with a 17ft. 3in. flood with a seven hour peak. The Buckley breach shows the protecti'on given to the railway by the board's stopbank system, and saved the adjacent subdivision from further flood damage. The Buckley breach at the new Te Maire floodgate shows the necessity of patrolling the stopbanks during high floods, and also giving special attention to new works and knowing weak places, which should be strengthened .at the most suitable time of the year. Considerable care was taken to consolidate the soil that was replaced over this floodgate, and ample height was provided for settlement." The meeting was attended by Messrs. J. Chrystall (chairman), J. B. Chrystall, G. M. Mitchell, L .J. Vile, F. Jackson, T. R. Saunders, R. J. Law, S. M. Newth, H. R. Farquhar and R. H. Spencer.