Large wood transport and jam formation in a series of flume experiments

Abstract

Large wood has historically been removed from streams, resulting in the depletion of instream wood in waterways worldwide. As wood increases morphological and hydraulic complexity, the addition of large wood is commonly employed as a means to rehabilitate in-stream habitat. At present, however, the scientific understanding of wood mobilization and transport is incomplete. This paper presents results from a series of four flume experiments in which wood was added to a reach to investigate the piece and reach characteristics that determine wood stability and transport, as well as the time scale required for newly recruited wood to self-organize into stable jams. Our results show that wood transitions from a randomly distributed newly recruited state to a self-organized, or jam-stabilized state, over the course of a single bankfull flow event. Statistical analyses of piece mobility during this transitional period indicate that piece irregularities, especially rootwads, dictate the stability of individual wood pieces; rootwad presence or absence accounts for up to 80% of the variance explained by linear regression models for transport distance. Furthermore, small pieces containing rootwads are especially stable. Large ramped pieces provide nuclei for the formation of persistent wood jams, and the frequency of these pieces in the reach impacts the travel distance of mobile wood. This research shows that the simulation of realistic wood dynamics is possible using a simplified physical model, and also has management implications, as it suggests that randomly added wood may organize into persistent, stable jams, and characterizes the time scale for this transition. Key Points:Unstable newly recruited wood adopts a stable configuration during a single flood event Stable jams form around large key members and ramped wood pieces Realistic wood dynamics can be reproduced in a physical model

A conceptual model of riparian forest restoration for natural flood management

“…It is probable that some, if not all, transported in‐stream wood will be trapped and deposited within the catchment (e.g. Braudrick et al , ; Gurnell et al , ; Bocchiola et al , ; Dixon and Sear, ), as stable large wood and logjams have been shown to be effective trapping locations for mobile wood in the channel (Davidson et al , ), furthermore, it is probable that some longer pieces less than 30 cm in diameter would also remain stable. Although these values will be an underestimate of total in‐stream dead wood biomass it is a useful measure of the likely relative abundance of logjam features in small and medium‐sized forest streams (Gurnell et al , ), furthermore total and average in‐stream wood volumes have been shown to be heavily dependent on the largest pieces of wood (e.g.…”

Modelling Spatiotemporal Dynamics of Large Wood Recruitment, Transport, and Deposition at the River Reach Scale during Extreme Floods

“…The modelling of the clogging process has to be improved in the future. Recently, some experiments showed possible ways to improve the modelling of this process [99][100][101][102]. For this question, we recommend using more detailed and fully coupled models, i.e., those in [60].…”

Observations of Channel Change from Constructed Wood Jams on a Forested Gravel‐Bed Stream

“…The interlacing or wedging of key pieces into standing live trees on the floodplain provides a way to increase the longevity of the jam without the need for the steel cables, bolts, and imported boulders used in standard practice. A growing body of research (Merten et al 2010;Davidson et al 2015;Wohl, in press) supports the importance of these factors in jam stability.…”

“…However, the composition and volume of jam material controls stream velocities and shear stress in and around the jam (Manners et al 2007). Piece irregularities, especially rootwads, play a large role in determining piece stability as shown in flume experiments (Davidson et al 2015) and natural settings (Merten et al 2010).…”