ENGINEER THINKS FLOODGATE EFFECTIVE

Manawatu Times, Volume LIV, Issue 6811, 15 January 1929, Page 2

ENGINEER THINKS FLOODGATE EFFECTIVE

Bui Could be Larger LAND NOT SUBMERGED LONGER TITAN USUAL MEETING TO BE CALLED. A report was submitted by the engineer (Mr. A. 11. M. Wright) to tho Munawatu Drainage Board yesterday relative tho controversy as to whether the floodgate and bridge recently erected at tho outlet of Bourke’s diain, Rangiotu, had unduly held back floodwaters in October last.

Mr. Wright stated: For reasons to be given I am of tho opinion that the land adjoining Bourko’s and Main drain was not submerged for a longer period than would have been tho case had there been no floodgato erected and also that in the latter case more land would have been submerged. I ?.m also of the opinion that tho total area of tho floodgatos could, with advantage, have boon made much greater, more particularly in the lower section. Should it be considered absolutely essential to increase the capacity of the floodgate, I am of the opinion that such increase should ho not less than 50 square feet below tho level of the second tier of floodgates. Unfortunately tho existing structure is so designed that it would be a most difficult and expensive work to add sufficient floodgates to obtain this capacity and in my opinion it would be easier end cheaper to construct a now culvert alongside, fitted with floodgates or penstock.” Prior to the erection of the floodgates the low-lying lands adjoining Bourko’s and Main drains were flooded from the following causes:— 1. As soon as tho level of water in tho Manawatu river rose it commenced to run back up these drains and from this alone was sufficient to submerge low-lying lands in times of moderately high flood. 2. In times of very high flood the Manawatu Tivor will over-run its banks in the vicinity of Jackeytbwn and waters run across Foxton lino. 3. Tho drains themselves, during heavy local rains may over-run their banks and flood adjoining land. 4. Mangaono stream over-running its banks and large quantities of this water finding its way into the Main drain causing it in turn to flood and over-run its banks.

Since the erection of the floodgate cause of flooding No. 1 has been eliminated or would have been if gates had not been interfered with. Tho improvements effected by the board to the Mangaono stream have already reduced tendency of this stream to overflotv its banks thus partially eliminating cause No. 4. Tho question then arises, is the capacity of floodgates under existing conditions sufficient to carry off tho reduced quantity of flood water from low-lying land as quickly as the original drain with all four causes of flooding operating. During times of flood in tho Manawatu river prior to the erection of the floodgate, a very largo quantity of water ran back up tho drains and over low-lying land as during the recent flood tho level of water outside the floodgate was at times at least six feet higher than inside.

It therefore appears certain that had there been no floodgate erected during period of flood last October, a groat deal of tho land would havo been submerged earlier than actually occurred and' that tho depth of water ovor the land would have been greater. Thoro is no doubt that at times the capacity of tho floodgates was insufficient' to permit of floodwaters inside being discharged at the same rate as the Manawatu river roccdcd, though the worst instance wc know of, the wator inside the gates was approximately three feet higher than outside. Settlers in tho district informed me, added the engineer, that prior to the erection of the floodgate after a big flood such as that experienced last October it was generally tbreo weeks boforo low-lying land was again free of water..

As previously reported scour is occurring on outside of gate, and on the western bank has already undermined abutment wall. We had prepared a schemo to remedy this which, although comparatively cheap, would prove effective. He estimated the cost of carrying out this work at £GS or, together with the cost of drecting a short length of stopbank already authorised at. this point, at approximately £75. Unless this work was carried out. the approaches to the bridge and later the bridge itself, were endangered, though ho was uncertain whether the County council, and through them the Highway board, w'ould contribute to the cost of the work.

Mr. E. Wood observed that if the Manawatu-Oroua River board’s scheme was gone on with, tho money spent on tho floodgate will have been thrown away. The chairman: “Absolutely, I think wo should wait and sec what the River board is going to do.” He further commented that it looked as if the Manawatu would get behind the floodgate if nothing was done. As regards the works that the Drainage board had done, it was never contemplated' that the overflow of the MunawutA &*al Oroua would be coped with

and settlers would have to put up with that inconvenience. Mr. Eliott: The whole thing in a nutshell is that when the basin fills with Oroua and Manawatu water, the floodgate doors aro too small to cope with the accumulation. The engineer reported that there was no blockages in Burke’s drain at tho present time. On the motion of Trustee Eliott, it was decided to call a meeting of settlers and "explain tho object of the relief channel. The engineer was instructed to prepare plans and data for the meeting. Mr. F. D. Herrick wrote hoping that the board would do something to increase the size of the floodgate. l?e i 3 to bo advised of the meeting with a request that he be represented. In a letter to the board, Messrs Harrison and Lett (Rangiotu) estimated their loss through accumulated water during the October flood, at £SOO or £ooo—a serious New Zear gift. They were also of opinion that the floodgates were too small and that tho board should tako steps to have the position remedied. Tho floodgate was a complete success, howevor, in closing down on tho. Manawatu for at least four days during the flood and if such had not boon the case, the water in their case would have easily reached the 1P26 level. However, in spite of the early closing of tho doors, tho water that flooded over took three times as long to got away.