WAIMAKARIRI RIVER AS WATER RESOURCE

Press, Volume CXI, Issue 32797, 23 December 1971, Page 11

WAIMAKARIRI RIVER AS WATER RESOURCE

In the accompanying article L. W. McCaskill reviews E. B. Dalmers recent report on "The Waimakariri as a Water Resource", a matter of considerable interest to farmers in the light of proposals to take water from the river for irrigation.

From the dawn of civilisation man has favoured the mouths and floodplains of rivers as sites for his cities, usually without attempts at anticipating the behaviour of the river he has adopted.

Once having occupied the flood-plain with dwellings, factories, houses of business, highways and railways, it is decided that floods are calamities which must be prevented from damaging or destroying the assets by building stopbanks, no matter what the cost. Having decided this, the encroachment is permitted of more and greater buildings and, installations on the floodplain, and such encroachment is used to justify the greater and greater costs of controlling floods by more, bigger, and better stopbanks. Christchurch has been no exception to the common pattern and since the early 1850 s engineers have been called on to carry out works which culminated in the Waimakariri River Improvement Scheme, 1960, estimated then to cost s2m, but with completion still four or five years away the total cost may well be considerably in excess of that sum. All this explains why the engineers over the years, and the various boards involved, especially the Waimakariri River Trust and (since 1944) the North Canterbury Catchment Board, have concentrated so much attention on peak discharges of the river in flood. The Water and Soil Conservation Act, 1967, under which the catchment board also became the regional water board, requires the board to investigate and record all significant resources of natural water within the region, and its quality and availability. Under the act the sole right to take natural water is vested in the Crown and all applications are adjudicated upon by the catchment board. The board soon realised it could not reasonably allocate water unless ’ it knew how much was available in various situations over the whole region. It was decided that

i the needs of Christchurch should have priority and in January, 1970, an examination of the Waimakariri River as a water resource was commenced. The need for the study became more urgent when irrigation committees were formed both north and south of the Waimakariri and quickly developed pro-

posals for taking vast amounts of water from the Waimakariri near the lower gorge, tentative plans providing for 2850 cusecs to be abstracted from the river and used to irrigate farm lands. Whether this amount of water, or in fact any water at all, could be made available became a vital question, and, as chief engineer to the catchment board, Mr Dalmer directed the elaborate study described in this book. The act requires that every regional water board “shall have due regard to recreational needs and the safeguarding of scenic and natural features, fisheries, and wildlife habitats, and shall consult the appropriate authority controlling fisheries and wildlife where they are likely to be affected.” All this has been done and Mr Dalmer has considered the needs of those using underground water, bathers, jet-boaters, campers, fishermen, picnickers, fish, birds, waterrace systems for farm stock, shipping, domestic water supplies, fire-fighting, irrigation, dilution of trade wastes and sewage, and, of course, the need for maintaining a drainage channel for discharges ranging up to 150,000 cusecs and for

transporting vast quantities of shingle and silt from the catchment of 1415 square miles. After a description of the catchment a summary is given of available information on precipitation; river flows generally follow the pattern of rainfall at Arthur’s Pass with an average rainfall of 184 inches. Then follows a mass of figures recording what has been ascertained about river flows since the first gaugings were made in 1866. Of special importance affecting the allocation of water, is that the lowest flow recorded at the Highway Bridge was 1225 cusecs on April 9, 1960. In recent years gauging has been much assisted by the use of jet boats; they were especially useful in February, 1970, when the Ministry of Works, at the request of the board, carried out a comprehensive series of simultaneous gaugings on one day at specific stations. These showed that Professor Speight’s views in 1927 were correct that between the Halkett and West Melton groynes much river water disappears underground to enter the artesian area under Christchurch. Over three miles the river under normal flow loses an average of 382 cusecs in this way. “The conclusion at the present time is that the users of artesian water in the area from Christchurch to Lake Ellesmere are users of Waimakariri water to the extent that their sup- ■ plies are drawn from aqui- i fers fed by infiltration from | the Waimakariri River.” Fishermen are a very i vocal section of the com- ■ munity when their rights, ; needs, or desires are under attack and Mr Dalmer ' wisely consulted the North , Canterbury Acclimatisation i Society on its views as to I the minimum discharge i necessary for fish life and I for fishing. Their recommended minimum at Wright’s Cut, just above the Highway Bridge, was 1650 cusecs. The other main organisation consulted regarding its needs was the Christchurch Drainage Board. It should be realised that a major service by the Waimakariri

River is; the dilution of polluted discharges into the lower foqr miles by about a dozen important industries. Mindful of its duties under various acts the Drainage Board says that it will oppose any reduction in the low flow of the river below 1400 cusecs. The only consideration which would alter the board’s views would be the purification of the various discharges before . entry into the river. And this will cost vast sums of money. But on the face of it unless this purification is brought about there seems little hope of the Waimakariri River being available as a large-scale irrigation resource.

Mr Dalmer does not' make recommendations for the allocation of water far any future use. This would be improper as the catchment board’s responsibilities are both investigatory and judicial and.it is not able to make any decision concerning the availability of water in advance of an application. But any person or organisation interested in applying for the use of Waimakariri water would do well to study the report Understanding of Mr Dalmer’s account is greatly helped by the excellent diagrams and by'the end-paper maps of the complete catchment The board is to be congratulated on publishing the report. More local bodies could similarly

take their constituents into their confidence.