Trends in the use of large wood in UK river restoration projects: insights from the National River Restoration Inventory

Abstract

Large Wood (LW) is increasingly employed in river restoration to promote physical habitat heterogeneity and ecological diversity. To explore how LW has been used in restoration schemes across the United Kingdom in recent decades, we analysed data on 912 LW projects archived in the UK's National River Restoration Inventory (NRRI). The number of LW schemes has continued to increase following the earliest records in the 1990s, largely tracking overall trends in river restorations. LW projects have been predominantly located in lowland, rural streams, although there has been a notable cluster in and around London. LW projects have mainly revolved around the desire to deliver hydromorphological improvements and specifically the creation of fish habitat. Most schemes used LW in simple deflector forms despite the growing scientific evidence of the benefits of using structurally complex LW. Post project monitoring has been limited and mostly restricted to photographic records. This type of database analysis can provide important insights and help guide future restoration practice.

Hydromorphological, hydraulic and ecological effects of restored wood: findings and reflections from an academic partnership approach

“…Restored large wood jams surveyed in the River Loddon catchment were structurally simpler than naturally occurring examples, containing fewer key pieces and extending only part way across the channel width. This is consistent with the tendency to use more conservative large wood features in restoration design (Cashman et al ., ), but more complex jams (e.g. Nisbet, ) may be more effective in delivering channel and habitat recovery (Harvey et al , ) and biodiversity goals (Thompson et al , ).…”

“…Growing recognition of the important role of large wood in river channels has led to increasing use of large wood in restoration schemes. There has been a tendency for large wood restoration to favour simpler flow deflectors over more structurally complex wood features (Gippel et al , ; Cashman et al ., ), reflecting concerns over increased stage and flood risk (Linstead and Gurnell, ) and the potential for mobilisation and risks to downstream structures (Gippel et al , ; Erskine and Webb, ; Roni et al , ). More recently, however, some projects have incorporated more complex wood jams (e.g.…”

“…Learning from past successes and failures in restoration is vital to the development best practice (Kondolf, ; Kondolf et al , ; Downs and Kondolf, ; Palmer et al , ). Unfortunately, opportunities are limited because of an overall lack of detailed and longer‐term project appraisal (Bernhardt et al , ; Kail et al , ; Morandi et al , ; Cashman et al , ). PhD and MSc research can make important contributions to post‐project monitoring and assessment of river restoration projects, with the potential for successive cohorts to extend the temporal reach of monitoring.…”

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).…”

Editorial

“…Dixon et al () develop this theme further by considering the time lag between the start of riparian forest growth and the age at which the forest can begin to deliver wood of sufficient size to the river to resist fluvial transport, anchor logjams and so increase channel morphological complexity and hydraulic resistance. Cashman et al () evaluate trends and patterns in the use of large wood for ecological restoration in UK river systems using information extracted from the National River Restoration Inventory. They find that, while the number of projects using large wood is increasing, there has not yet been a shift towards the emplacement of complex large wood structures that fully emulate those that might develop naturally.…”