TIDE-LEVEL CANALS PROPOSAL WAIHOU AND PIAKO RIVERS

Hauraki Plains Gazette, Volume 52, Issue 3244, 26 March 1943, Page 3

TIDE-LEVEL CANALS PROPOSAL WAIHOU AND PIAKO RIVERS

TOO MUCH WATER FOR CHANNELS

DEALING WITH LARGE FLOODS

FORMER LOCAL BODY ENGINEER’S OPINION

A proposal to construct tide level canals in the Waihou and Piako rivers to reduce the distance the water is required to travel to the sea in an effort to deal with heavy floods was outlined recently by Mr W. J. Gibbs, a fonder Piako County Council engineer, in an address to the Te Aroha Chamber of Commerce.

Mr Gibbs pointed out that with the reclamation of thousands of acres in the Awaiti, Piako, Kerepeehi and Ngatea districts flood waters had been confined to the rivers which had not large enough channels to take this additional volume of water.

PROPER OUTLETS

SEA-LEVEL CANAL URGED WOULD BENEFIT THE LAND SHOULD STRAIGHTEN CHANNEL The following is the address delivered 'by Mr 'Gibbs : — “During 1937 I suggested a scheme of river improvement and on September 21 of that year I put forward a scheme for raising the level of the lower football ground and shifting the river course in and to a canal to be constructed from the present traffic bridge to a bend in the river near Moon’s place. The spoil so removed from just near the traffic bridge and adjacent to the football ground was to be used to raise the level of and extend the fields of sports. “Further than this, I suggested a scheme for improving, straightening, widening and deepening the river to Paeroa. This would be a national scheme. • Paeroa’s Concern “On January 24, 1938, Mr Coulter and I attended a meeting of the Paeroa Chamber of Commerce with regard to this scheme, for river improvement. The people of Paeroa were concerned that if the scheme was carried out it would bring the flood water dowri the Waihou much more rapidly, and the peak of flood would coincide with the peak of flood in the Ohinemuri. “They state, as at present, that the peak of flood in the Waihou due to it (being absorbed in the filling up of the ponding areas and flooding of lands, is from 48 to 60 hours later than the peak of flood in the Ohinemuri. The Ohihemuri is made up of five or six small streams forming a basin with a quick run off and a length of about 20 miles from Paeroa whereas the Waihou extends to about 60 to '65 miles south of Te Aroha with a slow or flat run off. Tide-Level Canals “The Piako and Waihou rivers are main outlets for the efficient drainage of this district. A sea-level canal, or better still, a tide-level canal from the sea to near the junction with the Waitoa river, then a gradient to West road bridge on the Piako river, and from near Turua to the old overflow at Bancrofts, then a gradient on to Te Aroha, is required in both rivers. The channels should be straight enough and of sufficient capacity to carry away all flood waters that are now held in ponding areas and on farm lands. Such a development is of vital importance for it would bring in thousands of acres of land that are at present wasted.

“These main drainage canals can he and should te constructed and proper outlets to the Awaiti and Waitoa streams in the. Piako nver and to Te Aroha in the Waihou river. Farming has teen made possible m this district by the operations of drainage boards and the State, but as yet th! final outlets have not been constructed. Provision should be .made for larger channels when, (bridges are constructed over the ,pinko and Waihou rivers on the Pae roa to Pokeno railway. “The distance from Te Aroha to the sea by the river channel is about 47 miles and the fall about 27 feet, the gradient being about seven inches to the mile.' The river is affected by high tide to within two miles of Tirohia bridge so the greater proportion of total fall is between Te Aroha and Tirohia. The present channel froih the Puke bridge to about opposite Omahu is not of sufficient capacity in places to carry a heavy flood and should -be so constructed as to relieve any flooding near Komata or at “It is not possible to get the flood ■waters away by widening and deep-

ening the present river channel so many miles of new channels or canals should be constructed and distances between points greatly reduced. From Te Aroha to Mangaiti by river course is over six and a-half miles, while a line taken down the flooded area is only three and a-half and from Mangaiti to Tirohia bridge by the river course is eight miles whereas it is only four and threequarters along a line. This position also applies in the Piako river. Local Bottlenecks “At the present time there are two obstructions or bottlenecks in the river other than the general meander. These are near Tirohia (north of Bancrofts) and at Mangaiti bridge. “The dates of heavy floods in recent years are: 4/2/1917, 26/5/1924, 2-3/2/1926; 16-17/5/1937. Of these the 1917 flood was the highest at Te Aroha.

“In removing the bottleneck at near the old pond in Mr J• Strange s near the old pond in Mt J. Ctrange’s property and a new bridge erected over the canal where it would cross the present road. “Up until a few years back the flood waters of the Waihou ran across country in a very wide area to the Awaiti and over to the Piako and eventually out to sea. Now a stopbank has been constructed on the western side of the river from Bancroft’s at Tirohia to Strange’s, at Mangaiti. This has cut the flood waters off from thousands of acres of land in the Awaiti, iPiako, Kerepeehi and Ngatea districts. Confined to Waihou

“Confined to the Waihou, this water is now backed up over the road, railway line and several farms up to Mangaiti. Th? restricted river channel towards Turua has not been enlarged to take this extra volume of water, the channel from Bancroft’s northwards towards Paeroa is as it was before the overflow was cut off, and is not large enough to carry the extra flow.

“The rough measurement widths of river channels at the different bridges when the river is low, are as follows: Waiorongomai, river channel about 96 feet, bridge about 160 feet. Te Aroha traffic bridge, length about 406 feet, river channel about 110' feet. Mangaiti bridge, about 228 feet, river channel 162 feet. Tirohia bridge, about 507 feet, river channel ,150 feet. A channel with a bottom width of less than 300 feet is of little use to cope with flood waters in the Waihou. A very much smaller channel or canal would suffice for the Piako river.

“The restricted flow at the traffic and railway bridges in Te Aroha could be greatly improved by removing from the waterways up to 130,000 cubic yards of soil and silt; this could be used for filling or ‘ banks where required. “Since 1917 the river channel near and under the Railway bridge has silted up to a depth of 10 to 12 feet and for a width of 51 feet. Since the river boat has ceased running to Te Aroha the wharf approach has silted up for at least 30 feet in width. The rise of the river at the wharf in the 1917 flood was nearly 15 feet.”