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

Abstract

Large wood (re)introduction can deliver multiple benefits in river restoration, but there is a dearth of the detailed and longer-term post-project monitoring and evaluation required for improving best practice. We present findings from an academic partnership approach to post-project evaluation, based on successive MSc research projects on restored large wood in the Loddon catchment, UK. Field and modelling data reveal: (i) key differences in large wood features between restored and natural reaches; (ii) increased hydraulic retention and changes to mesohabitats associated with large wood; (iii) differences in macroinvertebrate community composition around large wood but a lack of site-level effects; (iv) interactions between macrophytes and large wood that may be specific to restored reaches; (v) a need for further field and modelling studies to inform the accurate representation of large wood in hydraulic models. Some key challenges in partnership working are identified to aid planning and effectiveness of future collaborations.

Adding large woody material into a headwater stream has immediate benefits for macroinvertebrate community structure and function

“…There was good support for the hypothesis that macroinvertebrate communities were enhanced by LWM installation at the reach scale. The significant increases in total density, total biomass, and taxon richness of macroinvertebrates in this study are contrary to the growing body of literature, which reports only minor effects of stream rehabilitation processes on macroinvertebrates (Hilderbrand et al, 1997; Roni et al, 2006; Testa, Shields & Cooper, 2011; Leal, 2012; Pinto et al, 2019), but they are consistent with some studies that compared rehabilitation outcomes with nearby natural systems and/or the status before rehabilitation. Smock, Metzler & Gladden (1989) found that macroinvertebrate abundance and biomass increased with an increase in the number of woody dams that led to the collection of organic matter and increased food availability in two low‐gradient, headwater streams on the Coastal Plain of Virginia, USA.…”

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

“…Comparative testing of different LW representations to determine the possible equifinality of predictions is also an area requiring more research. For example, in the study of Pinto et al (), for a low discharge (0.283 m 3 /s), using a blockage factor or Manning's n representations resulted in similar predicted stages. The most parsimonious approach that is adequately supported by previous validation should be chosen over preference to more complicated representations (e.g., addition of elements to meshes).…”

“…Thirdly, in relation to lowland rivers, the hydraulic interaction of LW with aquatic vegetation, remains underexplored in empirical‐ and model‐based studies and should also be considered (Pinto et al, ). Aquatic vegetation can generate significant flow resistance that can vary according to temporal growth patterns (O'Hare, Mountford, Maroto, & Gunn, ) and its coincidence with LW could potentially have synergistic effects on flow resistance.…”

“…This includes assessment of the suitability of approaches to represent stationary LW in numerical hydraulic and hydrological models (Nisbet, Silgram, Shah, Morrow, & Broadmeadow, 2011). To date, no accepted guidance or bespoke tools are available (Metcalfe, Beven, Hankin, & Lamb, 2018;Nagai et al, 2017;Pinto et al, 2019;SEPA, 2016). In part this reflects the difficulty of modeling such complex, porous features that vary considerably in form and setting (Figure 1; Abbe & Montgomery, 1996) but also the recently developed interest in the topic.…”

Editorial

“…They apply a newly developed river morphological survey (MoRPh) to evaluate channel and vegetation adjustments over a year in response to these restoration actions and in comparison with an unrestored (control) reach. Finally, Pinto et al () report on a series of small research projects conducted over several years on a single lowland river in a partnership between academia and environmental regulators to explore how large wood has impacted on multiple attributes of this river system (geomorphology, ecology, flood risk). On behalf of the guest editors and I, we hope you enjoy this edition of the journal.…”