Logjam fluctuations during the decade after a major blowdown along a mountain stream in the US Southern Rockies

Abstract

AbstractA blowdown in 2011 along a 1200‐m length of Glacier Creek in the Southern Rockies of Colorado, USA substantially increased the number of channel‐spanning logjams and initiated formation of a 100‐m‐long multithread channel segment. Annual logjam surveys during 2012–2020 indicate that these effects have persisted for a decade, with the number of logjams remaining high despite inter‐annual variations in the location of individual jams. No single logjam has remained in place continuously since the blowdown, but logjams tend to persist longest and to re‐form at sites with large ramp pieces from one or both sides of the channel and a lateral constriction created by bedrock or large boulders that can buttress the ramped piece(s) downstream. The most persistent logjams also form in secondary channels in the multithread section and logjams in the multithread reach tend to have larger backwater storage than logjams in the single‐thread reaches. The results presented here are unique in detailing changes in logjams during the decade following abrupt recruitment of a substantial volume of large wood to a mountain stream.