. Columbia River fisheries development program. Fisheries Columbia Stream Clearance and Improvement Another means that has been used by the Columbia River Fisheries Development Program to in- crease the abundance of salmonids in the Basin has been the construction of fishways and the removal or modification of both natural and man-made barriers affecting fish migration. These ac- tivities, authorized and directed by Section 2 of the amended Mitchell Act, have opened nearly two thousand miles of prime rearing and spawning habitat formerly inaccessible to returning adult fish. Although e
. Columbia River fisheries development program. Fisheries Columbia Stream Clearance and Improvement Another means that has been used by the Columbia River Fisheries Development Program to in- crease the abundance of salmonids in the Basin has been the construction of fishways and the removal or modification of both natural and man-made barriers affecting fish migration. These ac- tivities, authorized and directed by Section 2 of the amended Mitchell Act, have opened nearly two thousand miles of prime rearing and spawning habitat formerly inaccessible to returning adult fish. Although early efforts were directed to the area downstream of McNary Dam, in 1957 the Upper Columbia and Snake River drainages were included. A comprehensive survey was conducted which located, catalogued, and assessed the impact of any barriers. Each was evaluated on existing and potential spawning and rearing habitats. Priorities were assigned based on the surveys, engineering estimates, and projected results. With the exception of some projects in Idaho, construction was essentially completed by 1970. Two different types of obstacles were involved; those which could be removed or modified, and those that required the construction of a fishway. In the case of many of the natural barriers such as small waterfalls and cascades, it was possible to blast or otherwise modify the obstruction so that fish could pass upstream without difficulty. Blasting and use of bulldozers also proved effective in remov- ing man-made obstacles such as log jams, coffer dams and crib dams (Figure 26).. Figure 26 A crib dam on South Yamhill River, Oregon, before removal. Where barriers were larger or more permanent, it was often necessary to construct fishways over them. The fishways (or ladders) consist of a series of connected artificial pools through which a fish is able to pass over an obstruction (Figure 27). Those constructed under the program varied in size from the small ladders built over 8 to 10 foo
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