Impacts of river restoration on small-wood dynamics in a low-gradient headwater stream

摘要

Wood is an important element in many river systems, interacting with channel and floodplain geomorphology, hydrology and ecology. Restoration practices are increasingly re-introducing wood into streams and researchers have started to study the geomorphic and ecological effects of re-introducing wood into rivers. However, little research has attempted to quantify the impacts of river restoration (including the addition of wood jams) on wood retention. Based on tracing dowels to simulate small wood (ranging in length from 0.184 to 1.06 m and diameter from 0.006 to 0.035 m) in three study reaches before and after restoration, this study provides a detailed representation of the influence of restoration on small-wood transport and the relative importance of different trapping sites within a low-order meandering stream in the New Forest, UK. The research specifically addresses the following questions. (i) Does restoration reduce transport of small wood? (ii) Does restoration increase the frequency and type of small-wood trapping sites? (iii) Do wood jams trap more small wood than other trapping sites? (iv) Do shorter pieces of wood travel further than long pieces? The study has demonstrated that (i) different types of restoration have different effects on the frequency and type of small-wood trapping mechanisms, and hence also on small-wood transport; (ii) wood jams were the most effective structures for trapping small wood in this environment; (iii) shorter pieces of wood travelled further than long pieces. Channel-floodplain interactions were also found to be important, allowing the floodplain to function as a trapping site. Copyright (c) 2007 John Wiley & Sons, Ltd.