Coarse woody debris in stream channels in relation to river channel management in woodland areas

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Abstract
Although river channel management now generally uses soft rather than hard engineering techniques the considerable research achieved for woodland river channels has not been completely collated with reference to management implications. Research results from 22 research papers show how debris dams have a significant influence upon the morphological, the process and the ecological aspects of channels; vary in their permanence, and differ in stability according to the overall organic matter budget. A summary diagram contrasts the impact of dams on river channel morphology, process and ecology before and after dam removal. Four major types of specific recommendation about the management of channels in woodland areas are identified from 29 research papers are that (1) management should be undertaken against a background knowledge of the behaviour of coarse, woody debris under natural conditions and that the organic matter budget should be disturbed as little as possible; (2) logging operations should minimize the amount of disturbance to, and disruption of, channel processes; (3) management should optimize the maintenance of habitat diversity and minimize the ecological disturbance to the channel; (4) in some areas specific management practices may require the introduction of new material into the channel. These recommendations are applied to the New Forest, southern U.K., which has a long history of clearance and management of coarse woody debris and where the requirements for clearance in relation to fish, drainage, and aesthetic impact can be achieved by minimizing the amount of removal of material from the river channel. In managing channels with debris dams in woodland areas, it is desirable to work with the river in a holistic basin context.