The current state of the use of large wood in river restoration and management

Abstract

Trees fall naturally into rivers generating flow heterogeneity, inducing geomorphological features, and creating habitats for biota. Wood is increasingly used in restoration projects and the potential of wood acting as leaky barriers to deliver natural flood management by 'slowing the flow' is recognised. However, wood in rivers can pose a risk to infrastructure and locally increase flood hazards. The aim of this paper is to provide an up-to-date summary of the benefits and risks associated with using wood to promote geomorphological processes to restore and manage rivers. This summary was developed through a workshop that brought together academics, river managers, restoration practitioners and consultants in the UK to share science and best practice on wood in rivers. A consensus was developed on four key issues: (i) hydrogeomorphological effects, (ii) current use in restoration and management, (iii) uncertainties and risks and (iv) tools and guidance required to inform process-based restoration and management.

Is the Hyporheic Zone Relevant beyond the Scientific Community?

“…At river-basin-scale, improved land management practices can reduce fine sediment generation and delivery to the river (e.g., cover crops, buffer strips), which deposits on, and ingresses into, the riverbed, clogging coarse bed sediments [182,243]. In-channel measures can be used to narrow the channel, increase river flow velocities, and induce scour (e.g., willow spilling, flow deflectors, and natural riparian vegetation growth) to flush fine sediment from the riverbed, which increases hydraulic conductivity and promotes the formation of bedforms [244].…”

Functional traits of hyporheic and benthic invertebrates reveal importance of wood‐driven geomorphological processes in rivers

“…Finally, in the context of river restoration, large wood has been gradually integrated into management strategies as a means of improving the biodiversity and conservation value of lowland rivers (Grabowski et al, ; Larson et al, ). Yet, such approaches have not always given due attention to the ecological effects of physical processes potentially promoting ecological responses.…”

“…Large wood (LW; length > 1 m; diameter > 10 cm; Wohl et al, ), for example, is a natural hydrostatic driver of HEF (Krause et al, ), enhancing HEF by increasing riverbed roughness and creating hydraulic gradients (Lautz, Siegel, & Bauer, ; Mutz, Kalbus, & Meinecke, ). Large wood induces multiple hydrological (i.e., flow deflection and scour), geomorphological (i.e., sediment entrainment and transport) and chemical (i.e., organic matter deposition, nutrient retention) processes that are key to river ecology (i.e., habitat for invertebrates; Table ; Benke & Wallace, ) and to river restoration (Grabowski et al, ; Larson, Booth, & Morley, ). Reaches with LW are usually more geomorphologically and hydraulically heterogeneous in space and time than sites without LW (Gurnell, ; Gurnell & Grabowski, ; Krause et al, ).…”

Representing natural and artificial in‐channel large wood in numerical hydraulic and hydrological models

“…By affecting sediment transport processes, artificial wood placement is also an alternative to conventional engineering for managing sediment movement problems (Addy & Wilkinson, 2016;Brooks, Howell, Abbe, & Arthington, 2006;Shields, Knight, & Stofleth, 2006). Reflecting this range of different applications, artifical LW addition has become a popular river management tool in recent decades (Grabowski et al, 2019); for example, in the UK, it has greatly increased since 2008 and accounts for about one fifth of all restoration schemes (Cashman, Wharton, Harvey, Naura, & Bryden, 2019).…”