Managing snags and large woody debris

Contents

• Theme: Managing snags and Large Woody Debris
• Research notes 1: The importance of large woody debris surfaces for algal growth in lowland rivers
• Getting a Grip: Resnagging the River Murray
• Research notes 2: Some observations on the amount and distribution of large woody debris in Australian streams
• The riparian adventures of Eco-man and Dr Earth
• It's a Wrap: News from around Australia

Managing snags and large woody debris

Snags and large woody debris (LWD) are the sticks, branches, trunks and whole trees that fall into rivers and streams. LWD is important in streams and rivers from both an ecological and a geomorphic/hydraulic viewpoint. LWD provides important in-stream habitat for aquatic animals, as well as stable sites for the processing of carbon and nutrients. Through its impact on channel structure and flow, LWD also assists in the formation of habitat (such as scour pools). This latter process has led to the misguided belief that LWD also causes significant channel erosion. Another false belief is that snags significantly reduce channel capacity, leading to overflowing of banks during flood events.

These misunderstandings about the effects of LWD on erosion and flooding, has meant that snag removal programs have continued throughout Australia, even after the initial rationale for snag removal (safer river transport) had ceased to be relevant.The problems that exist in managing large woody debris are, therefore, not so much its negative impact, but the long and widely-held perceptions of its impact.

From the Editor

April 2000 already (!) and the Riparian Lands Program Phase One is wrapping up in time for Phase Two to begin in June 2000. I am pleased to announce that I have been appointed as the Program Coordinator for Phase Two, with Phil Price also working with me in this role over the next five years. We are thrilled to be able to continue working on a program that is committed to integrating science and practical experience in ways that promote and assist the improved management of rivers and riparian lands across Australia. Negotiations are now underway with many different groups about the priorities for investment, and opportunities for partnership in Phase Two of the Program.

Before we can move into Phase Two, however, there remains a great deal of work to be done in Phase One. The next few months will be spent ensuring that the results of the research undertaken in Phase One are converted into useful and relevant products for a range of different end-users. One of these products is RipRap, with this edition focusing on the issue of snag and large woody debris management. This topic was requested by quite a few readers, and we have tracked down the most recent research being undertaken across the country and combined it with information from the Riparian Land Management Technical Guidelines to provide a good overview of the management and R&D issues. I hope you enjoy this edition and, in particular, the cartoon that is thinking laterally about ways to better manage our riparian lands!!!

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