Will Fish Climb Big “Hurdle”?
UNIQUE PROVISIONS AT WAITAKI INTERESTING CONJECTURES AROUSED
Will the Salmon in the Waitaki surmount the big hurdle that has been placed in their path? That is a question which has been occupying the thoughts of anglers, who naturally are interested as to what effect the big dam is going to have on the fishing. The following information has been contributed by Mr R. H. Packwood, engineer-in-charge at the works:
American Practice Followed
One of the less conspicuous, but nevertheless interesting, adjuncts to the Waitaki dam will be the so-called “fish-ladder,” by means of which salmon may ascend to the lake created by the dam, and thence to the headwaters of the Waitaki river. In some States in America, the provision of a fishway is a legal requirement, designed to protect the interests of an important industry. Although in this country we have not progressed so far as that, it was decided to follow American practice at the Waitaki dam. The dam is divided into two main sections, namely, a spillway or overflow section 1200 feet long, and a non-over-flow section on which is located the power-house, 400 feet long. It is flanked on each end with strut wingdams, abutting on to Otago and Canterbury respectively. Under normal river conditions, the spillway will be overtopped by two or three feet of water, but during extreme floods, there may be as much as 12 feet. The overflowing water, in its descent of some 70 feet, will acquire a velocity of about 60 feet per second, and not even a super-salmon could be expected to negotiate so formidable an obstacle. A route through the intricate water-pas-sages and whirling turbines in the powerhouse is equally impracticable, so a small stream will be created by bypassing a little water through the sluice-gates in the wing-dam at the Otago end of the structure along which salmon can find a way up in easy stages. The “bed” of this stream will be of concrete, formed in compartments eight feet long, four feet wide and two feet deep, making a series of pools arranged one above the other in twofoot steps. By opening one of the sluice-gates at the top of the “ladder,” a regulated amount of water will flow down these steps, and when the stream meets the river channel below the dam. the turbulence it creates is expected to tempt salmon to investigate the way up the ladder. The length of the pools (eight feet) is considered to be sufficient to enable the fish to gain the speed necessary to jump the two feet rise into the adjoining pool, while at intervals longer ones are provided as resting places.
Steps on Retaining Wall
The ladder commences with steps moulded on to a retaining wall at the exit to the draft tube of the turbine nearest the Otago river-bank, and after zig-zagging up the adjoining hillside, terminates in another similar series of steps formed on the wingdam. Through the wing-dam there will be water . passages at different levels, and admission of water will be controlled by sluice gates operated from the crest of the wing-dam: Experience in America shows that salmon travel along well-defined routes, keeping always to one side or the other year after year. It is recorded that when such a route has become blocked by the headworks of a power scheme, they will exhaust themselves to death in a vain attempt to fight their way up the turbulent waters of the draft-tubes of the turbines, rather than seek & route elsewhere. No doubt, as in the case of migratory birds, adherence to a particular route is instinctive, derived from centuries of forbears who have followed the same road. Whether or not a fish-ladder is going to be successful, therefore, cannot be foretold. Our Waitaki salmon have only a few years of New Zealand history, and may not in that time have acquired the impulse whicn leads •their American cousins along the same route throughout the centuries. Nevertheless, the task of “educating” them will be full of interest. The fact that the Waitaki is subject
to violent floods during the summer and autumn, and particularly so during March and April when the salmon are running complicates the local problem. The variation in the water level of the lake created by the dam may be as much as 12 feet, and to meet this condition, the water passages through the dam, as well as the sluice gates controlling the flow of water through them, have to be arranged at various levels to suit varying conditions of the river. In some seasons, it may occur that, due to melting snows on its alpine watershed, the floods may be prolongued throughout the entire season when salmon are running, and the minor disturbance caused by the small stream pouring down the fish ladder may be imperceptible, especially as the river is always highly discoloured at such times.
The effect of the 2000 acre artificial lake above the dam towards clarifying the water will be negligible, as it will be a mere pond in comparison with the three natural lakes which feed the Waitaki, and through which flood waters now pass without any noticeable change of colour. The fish ladder is being designed by engineers of the Public Works Department, in collaboration with the Chief Inspector of Fisheries, and much useful information has been obtained from America. It will be realised, hdwever, how largely experimental the project will be, and the designers themselves are by no means sanguine that it will prove entirely successful. It is interesting to note that the fish ladder has been put in voluntarily by the Public Works Department, as there is no legal enactment in New Zealand making such a course compulsory. In England and America there are such laws and in the United States some extraordinary difficulties have been encountered in complying with the law. In some dams lifts or, as they are there called, elevators have been provided to carry the fish over the great obstacles.
An Angler's Paradise
When the lake has been formed at the Hydro the Waitaki Acclimatisation Society will stock it with rainbow trout. Situated as it will be, the lake should become an angler’s paradise. Another proposal is that the slopes surrounding the lake be planted with trees. This has been the subject of consideration by the Waitaki County Council and Oamaru Beautifying Society. It is very likely that quite a substantial area will be planted, but nothing can be done until the definite high water level shore of the lake has been defined.
The Chief Inspector of Fisheries (Mr A. E. Hefford) submitted a plan for the ladder to the Fish Conservation Board of America and this body replied that the plans should meet the requirements of a very difficult position. It was. however, not definite that they would. With numbers of anglers in this district the salmon is not at all popular, it being contended that they have spoilt the Waitaki as a trout stream. These anglers would not be sorry to see the salmon leave the river for good, but there is a danger that, if the ladder fails, the salmon might head up the Hakataramere river, which is still a good trout stream.
As to what will happen when the dam is closed and the lake is in process of filling, it is stated that there should be ample water downstream for the fish. The two permanent sluiceways in the dam will be used and, as these are capable of carrying more water than has been in the river during several recent weeks, there should be an ample flow below the dam. In addition this will, of course, be supplemented by the waters of the river’s tributaries the Hakataramea and Maerewhenua rivers—lower down. The maintenance of flow below the dam will result in the lake being, filled more slowly than would be the case if the dam could be completely shut.
Permanent link to this item
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Bibliographic details
Timaru Herald, Volume CXXXVIII, Issue 19941, 27 October 1934, Page 6
Word Count
1,331Will Fish Climb Big “Hurdle”? Timaru Herald, Volume CXXXVIII, Issue 19941, 27 October 1934, Page 6
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