The influence of geomorphology on large wood dynamics in a low gradient headwater stream

Abstract

Understanding large wood dynamics is critical for a range of disciplines including flood risk management, ecology and geomorphology. Despite the importance of wood in rivers, our understanding of the mobility of large wood remains limited. In this study individual pieces of large wood were tagged and surveyed over a 32 month period within a third and fourth order lowland forest river. Individual pieces of wood were found to be highly mobile, with 75% of pieces moving during the survey period, and a maximum transport distance of 5.6 km. Multivariate analyses of data from this study and two other published studies identified dimensionless wood length as the important factor in explaining likelihood of movement. A length threshold of 2.5 channel widths is identified for near functional immobility, with few pieces above this size moving. In addition, for this study, wood type, branching complexity, location and dimensionless wood diameter were found to be important in determining mobility only for sinuous reaches with readily inundated floodplains. Where logjams persist over multiple years they were shown to be reworked, with component pieces being transported away and replaced by newly trapped pieces. The findings of this study have implications for river management and restoration. The high mobility observed in this study demonstrates that only very large pieces of wood of length greater than 2.5 channel widths should be considered functionally immobile. For pieces of wood of length less than the channel width the possibility of high rates of mobility and long transport distances should be anticipated.

Natural vs anthropogenic streams in Europe: History, ecology and implications for restoration, river-rewilding and riverine ecosystem services

“…In headwater streams the role of wood varies since the processes of supply are influenced by slope processes (shallow landslides) and channel width:wood ratios (Dixon and Sear, 2014). Large wood recruitment in headwaters can block valleys forcing aggradation of the valley floor (Montgomery and Abbe 2006).…”

Geomorphic and stream flow influences on large wood dynamics and displacement lengths in high gradient mountain streams (Chile)

“…Consequently, to take advantage of the benefits of LW and to prevent its potential negative impacts in the case of floods, natural LW dynamics must be managed properly (Mao, Andreoli, Iroumé, Comiti, & Lenzi, ; Mazzorana et al, ; Wohl et al, ). However, our understanding of wood entrainment and deposition processes is still limited (Dixon & Sear, ; Schenk, Moulin, Hupp, & Richter, ) and largely restricted to a small number of field‐based (Ravazzolo, Mao, Picco, & Lenzi, ); laboratory (Welber, Bertoldi, & Tubino, ); or modelling (Ruiz‐Villanueva, Wyżga, Hajdukiewicz, & Stoffel, ) approaches, typically hampered by short measurement periods and a limited number of tagged logs. Therefore, a better understanding of geomorphic and stream flow influences on LW dynamics, and tools for the quantification of displacement lengths and entrainment and deposition processes are still needed and are a prerequisite for proper management of wood transport volumes and related hazards.…”

“…Martin and Benda () report that in narrow (about 3–5 m wide) channels, the probability of a LW piece being transported at least 50 m is 90% but only 10% of the pieces would, at the same time, move more than 300 m, whereas in 20‐ to 30‐m‐wide channels, LW is likely to travel at least 300 m with a 90% probability. However, the displacement distance of a LW piece is significantly related to other factors, such as branching complexity, wood type, and decay (i.e., density), and this renders the process highly variable and is also difficult to predict (Dixon & Sear, ). Moreover, LW is routed more quickly and stored for less time in confined reaches, but mobility and displacement lengths are limited during low flows by coarse substrate and other obstructions (Kramer & Wohl, ).…”

Large wood recruitment and transport during large floods: A review

“…al., 2013;Dixon and Sear, et al, 2014;Boivin et al, 2015; Ravazzolo et al, 2015b;Ruiz-Villanueva et al, 2015b;Ulloa et al, 2015), but only a few studies analyzed quantitatively LW transport during large floods. Such studies are of paramount importance to gain insights into the 'real' wood dynamics during high-magnitude events.After the 2005 flood in Switzerland (discussed in the previous section) and in addition to wood recruitment processes, locations and volumes of LW depositions also were identified and quantified in the four investigated catchments (Kander, Kl.…”