PROTECTING SALMON

Evening Post, Issue 149, 20 December 1935, Page 9

PROTECTING SALMON

COLUMBIA RIVER RUNS

BONNEVILLE DAMS

LADDERS AND LOCKS

The commercial harvests obtained j from salmon in New Zealand, though j no doubt satisfactory to the small operatives who devote their time to it in the season, are negligible when compared with the enormous yield of the great American rivers, which has resulted in a huge industry. Thus the problem of fish-ladders, which in New Zealand is regarded by many people as a fad for the edification of anglers, is in America regarded very seriously indeed. The great hydro-electric dams, raising the level of rivers, which are many times the size of.the largest.in New Zealand, present difficulties which it would require a vivid imagination to visualise in this country. .What is being done at the Bonneville Dam, on the Columbia CRiver, is described in "Pacific Fisherman" as "exceeding in concept and magnitude any programme hitherto undertaken by man to protect migratory fish against the perils of advancing civilisation." These works have met with the approval of the fishing and packing industries, the fish and game authorities of Washington and Oregon, the United States Bureau of Fisheries and the War Department, which is constructing the dam, with but two points on which they are in doubt; the adequacy of the collection system for upstream migrants and the adequacy of the collection system for downstream migrants. The problem exceeds in i difficulty any similar problem hitherto presented. It consists in passing a vast number pf salmon bound for-their spawning beds over an obstruction standing 72ft above mean low water, and in returning to tidewaters their tiny progeny, and the task must be carried out on a river flowing as much as 800,000 cubic feet of water per second. Moreover, the flow of the river varies'with the seasons down to less than 100,000 cf.s., while the level of the river below the dam alters as much' as 40ft. There are two dams, the powerhouse dam, lying between Bradford Island and-the Oregon bank,of the Columbia River, and the spillway, or main dam, lying between Bradford Island and the Washington bank of the river. UPSTREAM MIGRANTS. For upstream, migrants the provisions made are as follows:—(1) Tanner Creek canal, a channel cut in the ■: Oregon bank from a point above the dam to Tanner Creek, which enters,the river a mile downstream. The canal will be 40ft wide, and the fish climb by a series of steps, each' of one foot. Pools between steps ace a minimum of 16ft long, while in one case the distance between the jumps will be 1300 ft. (2) The navigation lock, primarily intended .for vessels with a draught not exceeding 26ft, connected with' the fish! collection system on the power-house dam. (3) A collection system extending right across1 the eh tire face of the power-house structure, consisting pf a channel in the power-house wall above the draft tubes. Water pouring from forty-one openings, each 9ft wide, is expected to attract the fish, which will have to jump about a foot through the openings. A current runs in the channel. Once the fish are in, it is expected to lead them; to cither the. navigation lock or a pair of fish locks which allow the water to be • raised to that of the river above the dam. (4) A pair of fish .locks, in which a perforated floor rises with the water,' arid gates let the fish out when the lock' is fulL These locks are worked alternately. (5) A fish-ladder rising on Bradford Island from the north end" of the power-house dam. This ladder is 30ft in width at its lowest point; and most of it is 40ft wide. Each of the pools in the ladder is 16ft long, and the jump between is only a. foot. (6) At the spillway dam,: between Bradford Island and the Washington... bank of the river, there is a collection system at each end of the dani;7 with screens which lead the fish to fish-ladders or locks, which are similar to those.being built in connection with the other dam. DOWNSTREAM MIGRANTS. For downstream migrants there* are the Tanner Greek canal, the navigation lock, a "flngerlirig" pass through the dam (in effect a steep fish-ladder), an ice sluice—primarily designed to prevent ice and trash entering the power wheels, but affording an opportunity for small fish to pass down the dam—and the Bradford Island and north bank fish-ladders. There are some who doubt that the scheme, when complete,' will, attract 'the fish. Possible unforeseen eddies may be encountered, .and some consider that; the number of gates is insufficient. What will happen to downstream bound fingerlings which miss their collection system and are drawn into the power wheels, 23ft in diameter, turning at only seventy-five revolutions per minute, is also unknown, though many consider, as there is room below the wheels, that the damage to either young.or adult fish would be light. ■'■:.,, ■.'-■•■ The magnitude of these fish-protec-tive works is staggering, and the cost some £720,000/ and probably more,' but the.cost is much" less than the annual value of the Columbia River salmon. These fishways will require when ;in use 8000 cubic feet of water every second, or 5,170,000,000 gallons a day. ."There can be no decision by trial and error," says the "Pacific Fisherman." "If the flshways do not work in the first year of their installation that cycle of the Columbia River salmon run will be wiped out for ever. In view of this all agencies participating in the project have sought to make every poss; /ie-provision for saving the fish." ; ■ . -,: '