RIVER CONTROL

Press, Volume XCII, Issue 27735, 12 August 1955, Page 3

RIVER CONTROL

Work Of Catchment Board Discussed ADDRESS BY CHIEF ENGINEER “I do not think we have yet experienced the maximum flood in any of our rivers,” said the chief engineer of the North Canterbury Catchment Board (Mr H. M. Reid) in an address to the Canterbury branch of the Professional Engineers’ Association of New Zealand. The meeting, which was an open one, was well attended by the public, who also saw two films dealing with soil erosion and the Waimakariri river. Speaking on river control and the general functions of catchment boards, Mr Reid said that there had been a great deal of confusion and misunderstanding in the past as to the works involved in river control and more especially as to the general functions, works and responsibilities of catchment boards. The work of catchment boards was all long term policy and in many cases it was impossible to provide satisfactory control works without a great deal of investigation, he said. Staff shortages were affecting that. A few of the North Canterbury Catchment Board’s activities were river control works, involving bank protection, groynes and other training works, channel clearing, stop banking and flood prevention works; soil conservation; and land drainage. Criticism of catchment boards had been particularly severe from some local bodies. “In some cases rivers within a catchment board’s territory traverse many local authorities’ areas and I fail to see just how adequate and efficient control of such rivers could ever be established with each local authority responsible for its respective length,” said Mr Reid. Run-off of Flood Waters Discussing river control, Mr Reid said that when a gravel bearing river reached the state of the Waimakariri, with a gradually flattening grade towards the sea, and a heavy bed load to be transported, trouble must be anticipated, particularly in the lower reaches. If the run-off of flood waters from the upper catchments of rivers could be slowed down, it would have a beneficial effect on the lower reaches. “I consider every £ spent to achieve this will pay dividends in the future.” Before any control scheme could be devised, record? were required of rainfall, run-off from the various catchments, and its effect on the river. Existing instruments were accurate for flows up to 15 feet a second, but not reliable for the higher velocities in the upper reaches during high floods. “At the Waimakariri Gorge bridge we believe velocities reach at least 25 feet a second, or more than 20 miles an hour,” he said. After discussing methods of control, including groynes, stop-banks, dredging, dams, and detention areas, Mr Reid said: “It is unfortunate that finance always seems to be one of the main stumbling blocks to success. In the past it has definitely been the main obstacle to works, but the position iS becoming somewhat easier as the importance of soil conservation and rivers control work becomes more evident to all. Of what use is it to plan huge public works unless some precautions are takeh to protect the land, our heritage? “Generous Subsidies” “The Government now provides boards with quite generous subsidies for approved river and conservation works and provided catchment boards can raise the local share of the cost, capital expenditure is assured within reason. However, many major control schemes have already been approved and others are in preparation so that as time goes on more and more Government assistance will be required. “Once again this is a case for education and it is our z hope that one day the whole < population will cooperate and impress on the Government the need for adequate finance to carry out these most important works. “Immediately after capital expenditure the question of maintenance arises. Catchment boards are fully alive to this angle and will not allow works to deteriorate for want of maintenance, as so many works have done in the past. Unless adequate maintenance is undertaken by the controlling authority it is quite possible for the whole of the original expenditure to be lost within a few years. This has already happened in a number of places and I consider maintenance work to be just as important as capital expenditure,” he said. Mr Reid said the problems were the coverage of the catchment areas with adequate rainfall stations; thq measurement of floods and the installation of further recording stations; the assessment of run-o.; the reduction of flood discharges: aggradation and its vices, including upstream and local erosion; the disposal of bed load; stabilisation of river banks;' flood prevention; and maintenance of' completed works.