. Protecting and enhancing America's forests and rangelands : 1986 research accomplishments. Forests and forestry United States; Rangelands United States. Providing Structures To Improve Fish Habitat: What Natural Obstructions in Streams Tell Us Resistant obstructions in and along stream channels, such as large woody debris, bedrock outcrops, or rooted bank projections, are vital to fish habitat. They greatly diversify aquatic habitat by disrupting the even flow of water and sediment downstream and by causing pools to scour and spawning gravels to deposit. In the past decade or so, fishery man
. Protecting and enhancing America's forests and rangelands : 1986 research accomplishments. Forests and forestry United States; Rangelands United States. Providing Structures To Improve Fish Habitat: What Natural Obstructions in Streams Tell Us Resistant obstructions in and along stream channels, such as large woody debris, bedrock outcrops, or rooted bank projections, are vital to fish habitat. They greatly diversify aquatic habitat by disrupting the even flow of water and sediment downstream and by causing pools to scour and spawning gravels to deposit. In the past decade or so, fishery managers have attempted to improve habitat by adding artificial structure in the form of logs, boulders, and gabion weirs, and by controlling inputs of large woody debris. Though the success of most of these efforts to increase fish production remains unknown, there have been some obvious successes and failures to create the desired changes in physical habitat. The success rate in a variety of streams can best be improved by understanding better how natural obstructions affect channel processes. This year, scientists of the Pacific Southwest Station completed a study on how natural obstructions affect fish habitat in a California stream supporting runs of both coho salmon and steelhead trout. Large obstructions were found to stabilize the stream channel despite the large volumes of sediment transported downstream. The channel changed only where large woody debris had moved. Obstructions were important for the distribution of habitats as well. Of the pools where larger fish resided in summer, most (85 percent) were formed by scour around obstructions. Bars, where spawning gravel was stored, were deposited upstream and downstream of obstructions. These results highlight the need to maintain numerous, stable obstructions in fishery streams in order to keep a diverse and stable habitat. Additional findings from this research provide specific guides to design of artificial habitat impr
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