TYPICAL PROBLEM

Hauraki Plains Gazette, Volume 56, Issue 32898, 20 August 1947, Page 5

TYPICAL PROBLEM

ROTOKOHU AREA FLOODS

ENGINEERS TO REPORT CATCHMENT BOARD ACTION An example of the problem that the Hauraki Catchment Board had to deal with, which he termed as typical of what was being experienced in the whole of the Thames Valley area, was put before the July meeting of the board by Mr H. R. Thorp, when he brought the notice of the meeting to a petition from the residents of the Rotokohu-Tirohia area for assistance in flood control. Mr Thorp outlined the history of the Tirohia-Rotokohu Drainage Board, giving some details of the flooding that had occurred in the area, and made some suggestions as to how the problem could be attacked.

“In the early days of settlement • this area of approximately 6000 acres from the junction of the Waihou and Ohinemuri rivers to the foothills was mostly under water. The less swampy portions carried heavy kahikatea bush and good stands of flax,” Mr Thorp said in his-report on the history of the drainage of the . area. “ The drainage operations of the settlers met with varying results, according to the nature of the swamp,

and the various levels of the clay

bottom. About 1910 most of this land z was unwatered by several main drains that were cut by individual settlers, but most of the area was in an un-. developed state. The prospect of developing the lower, or northern, portion, of this area at this date was not bright, owing to the periodic flooding which took place from the Ohinemuri river which, was rapidly being choked up with mining tailings. “ In fact the floods were so frequent and the- tailings were so damaging to pastures that many of the settlers were in desperate straits. This state 'Of affairs culminated in the Waihou and Ohinemuri Rivers Commission after the disastrous flood of March,

1910, when much stock was lost and portions of the Waihi-Paeroa and Paeroa-Te Aroha railway lines were washed away. Much damage was also caused to the roads and bridges. “ As a result of the findings of the

1910 commission the Waihou and Ohinemuri Rivers Improvement Act was passed. The main purposes of this Act were the prevention of flooding by the improvement of the two rivers and the construction of stopbanks. *

“ Soon after this work commenced it was found that internal drainage was necessary as the stopbanks blocked most of the settlers’ main drainage outlets as well as many natural waterways.

“ The Tirohia-Rotokohu area was most adversely affected in this respect and the settlers pressed for some relief. The whole area was surveyed and levels taken. Various schemes were considered and finally two main outfall drains were constructed to link, up with the settlers main drainage system. These were the Tirohia drain and the Rotokohu drain which joined in the vicinity of Mill road and then continued north to an outlet on the Ohinemuri river just above the junction of the Waihou, with a large three barrel floodgate. Further up the Ohinemuri river a two barrel floodgate was provided on Cooper’s drain and another three barrel gate, constructed on the Kaouiti stream. ■ “ Some five miles of drains were dug with a dipper dredge which left- a large drain with a very rough bottom and batter. For some years these drains were left without maintenance and owing to weed growth and swamp settlement they got into a very a' J state. This state of affairs continued until 1928 when by strong representation from the settlers these di were reconstructed and the whole area was put under the control c" 'he newly constituted Trrohia-Hmohmu Drainage Board. _ i “ This board immediately extern w_; its operations to include the con tio-n and improvement of all the mam outfall drains in the area. The work was the reconstruction of the Kaouiti stream for which a loan wn raised for £BOO, and, with a Government subsidy of £1 for £2, was completed in 1930. ■‘The first maintenance rates we’? struck in 1930 and were at the rat-3 of lid in the £ on the rateable value and were levied on a classifies, xmi basis. The problem which now faced the board was to maintain some seven miles of machine cut drains and about eight and a-half miles of hand At outfall drains on the small amount of money collected from these ratm. In 1944 it was found necessary co

apply for assistance from the Soil Conservation and Rivers Control Council to re-dredge about 365 chains of these large drains. This work was subsidised by the soil council at £2 for £1 and the work was carried out by the Public Works Department and completed in December, 1945. “ At the same time the board approached the Ohinemuri County Council for assistance and after some consideration that council agreed* to pay the 'board £1 for every £4 spent by the board on the general maintenance of its drains.

“ The position of the .board today is sound financially. The Kaouiti stream loan has been paid' off and when the yearly drain cleaning operations are completed the board will finish the financial year with a small overdraft at the bank and no other commitments. The settlers in this part of the area are prepared to do all they can, but if assistance is riot ■given to them much of this area will go out of production,” Mr Thorp’s report concluded.

After presenting his report Mr Thorp said that he wanted to obtain a report from drainage engineers giving their views on the improvement of the drainage of the area. The possibility of relieving the settlers from flooding had to be considered because the area would be first class dairy land if it could be un-watered. The drains as they were, Mr Thorp said, never got the maximum draw-off except in dry weather, because of the short time of low mean tide in the river. The obvious solution to that, he said, was the installation of pumps and floodgates. The floodgates were already there, and working very well, but the economic possibility of pumping was very questionable because of the foreign water and also the great length of lead in the outfall drains at a very small fall. The total area of the catchment was about 9000 acres, including about 3000 acres of hill country. An alternative to the pumping scheme, Mr Thorp said, would be to stopbank main outlets from the area and lead the water into the Waihou river.

Mr Thoi‘p moved that a report on the area he made hy Works Department engineers, in which they could •give theii’ opinions on the control of floods in the area. In seconding the motion, Mr D. G. McMillan stated that there was insufficient drainage on the top side of the railway line and the •pasture would be ruined for some considerable time from the flooding.

The meeting decided to ask-for the report suggested by Mr Thorp.