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Natural variability in the distribution, loading and induced scour of large wood in sand‐bed forest streams
Author(s) -
Webb Ashley A.,
Erskine Wayne D.
Publication year - 2005
Publication title -
river research and applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.679
H-Index - 94
eISSN - 1535-1467
pISSN - 1535-1459
DOI - 10.1002/rra.839
Subject(s) - bedrock , streams , debris , hydrology (agriculture) , geology , large woody debris , channel (broadcasting) , stream power , coarse woody debris , habitat , logging , volume (thermodynamics) , environmental science , geomorphology , sediment , ecology , geotechnical engineering , oceanography , biology , computer network , engineering , riparian zone , computer science , electrical engineering , physics , quantum mechanics
Characteristics of large wood and its influence on bed scour and pool formation have been investigated in four sand‐bed forest streams in southeastern Australia. Sites included high‐energy bedrock‐confined streams near Sydney and medium to low energy partially terrace‐confined streams on the south coast of NSW and in East Gippsland, Victoria. Total large wood loadings were inversely correlated with bankfull specific stream power. At the two lower energy sites, up to 18% of the total large wood volume comprised Tristaniopsis laurina trees living within the channel. At all sites, the majority of large wood pieces were small in length and diameter. However, the overall large wood volume was dominated by larger pieces. At the two lower energy sites less than 3% of large wood pieces formed part of debris dams, the majority occurring as individual logs. Debris dams were absent from the higher energy sites. The length of channel classified as pool habitat and the amount of head loss over log‐steps were positively correlated with large wood loading. A greater proportion of large wood pieces was aligned parallel to the flow at the higher energy sites. Such characteristics significantly influenced the type and extent of pools present. Longitudinal, bedrock and boulder scour pools were dominant at the bedrock‐confined sites, while transverse scour pools, log‐step pools and debris dam pools were dominant at the less laterally confined sites. The log‐affected pools were significantly smaller, in terms of length and maximum depth, at three of the study sites, than the non‐log‐affected pools. However, this study indicates that reintroduction of large wood into sand‐bed streams will increase bed scour, pool formation and hydraulic diversity. Copyright © 2005 John Wiley & Sons, Ltd.