All Logjams Are Not Created Equal

Abstract

AbstractLogjams create diverse physical and ecological effects in stream channels, including at least temporary storage of water, sediment, and particulate organic matter. We hypothesize that logjams that span the entire bankfull channel width in channels ≤25 m wide are more effective in storing these materials than non‐channel spanning logjams. We test this hypothesis by systematically comparing characteristics of 183 logjams from 17 stream reaches in the Southern Rocky Mountains. Our data set is novel in that it evaluates naturally occurring logjams in unaltered streams in a single study area specifically based on whether they span the stream channel. We find that channel‐spanning logjams have a significantly larger number of wood pieces, longer & wider pieces, more ramp and bridge pieces, and greater logjam height and volume, both as raw data and when standardized by average channel width. Channel‐spanning logjams also have significantly greater backwater pool volume and volume of particulate organic matter stored in backwater pools and in logjams. Restoration employing engineered logjams in relatively small channels currently focuses on non‐spanning logjams, but could be expanded to include spanning logjams.