Special Issue "Impact of Large Wood on River Ecosystems"

A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Hydraulics and Hydrodynamics".

Deadline for manuscript submissions: closed (30 November 2021).

Special Issue Editors

Dr. Isabella Schalko
E-Mail Website
Guest Editor
Massachusetts Institute of Technology, Cambridge, MA, United States
Interests: environmental fluid mechanics; flood assessment; physical modeling; sediment transport; turbulence structures; wood dynamics in rivers
Dr. Volker Weitbrecht
E-Mail Website
Guest Editor
Laboratory of Hydraulics, Hydrology and Glaciology, ETH Zürich, Zurich, Switzerland
Interests: environmental fluid mechanics; physical modeling; experimental techniques; river revitalization; flood assessment; river bed stabilization; airborne river monitoring; mixing and transport processes

Special Issue Information

Dear Colleagues,

Large wood (LW), also referred to as instream wood or driftwood, is a relevant part of a river ecosystem, commonly used for restoration and interacting with river engineering structures. LW in rivers creates heterogeneous flow conditions and morphological structures. LW accumulations may form ecologically beneficial dead water zones, thereby enabling the storage of nutrients. In addition, LW accumulations provide habitat for many different species and increase hyporheic exchange. To improve river restoration efforts, it is important to understand the LW transport dynamics and how LW affects and interacts with flow, sediment, and fauna.

Recent floods demonstrated an increase in sediment and wood-laden flows, which affects the design of hydraulic structures. Current river engineering structures impair the ecologically required sediment and LW continuity during low flows. Therefore, innovative monitoring and design concepts are required that sustainably manage sediment and LW transport.

This Special Issue focuses on the impact of large wood on river morphodynamics and the related ecosystems. We invite contributions that study wood transport dynamics and the interactions between wood, flow, sediment, or fauna to inform restoration efforts. We further encourage studies on sustainable wood management in rivers, including innovative technical solutions.

We invite contributions using field, laboratory, or numerical approaches. Original research papers, case-studies, and critical reviews will be considered.

Dr. Isabella Schalko
Dr. Volker Weitbrecht
Guest Editors

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Ecohydraulics
  • Environmental flows
  • Driftwood
  • Instream wood
  • Large wood
  • Flood control
  • Wood hazard assessment
  • Wood transport dynamics
  • Wood–sediment interaction
  • Wood–fauna interaction

Published Papers (5 papers)

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Research

Article
Ecosystem Services of Large Wood: Mapping the Research Gap
Water 2021, 13(18), 2594; https://doi.org/10.3390/w13182594 - 20 Sep 2021
Viewed by 596
Abstract
It is well known that large wood affects geomorphic processes and functions in rivers. It enhances the quality of the habitat but it can also cause a threat to the population. These processes and functions of the environment can be transformed into ecosystem [...] Read more.
It is well known that large wood affects geomorphic processes and functions in rivers. It enhances the quality of the habitat but it can also cause a threat to the population. These processes and functions of the environment can be transformed into ecosystem (dis)services, which represent direct or indirect (dis)benefits that the society obtains from nature. The goal of this paper was to describe the current relations between large wood and ecosystem services and map the related knowledge gaps. Firstly, we conducted a systematic literature review that was elaborated according to the six-stage and PRISMA protocols and workflow diagram. We found 499 papers; however, only 137 were eligible for the following analyses. Secondly, we made a transformation of research information from the articles (n = 135) into ecosystem services. The highest number of ecosystem services detected in the articles belonged to the regulation and maintenance section (n = 126), followed by the provisioning (n = 15) and cultural (n = 11) sections. The detected classes with the highest frequency of studies were specific habitat creation and increased channel heterogeneity. The findings show that the number of research papers on this topic is still insufficient; however, anaylzing ecosystem services could be useful to advocate the presence of large wood in the rivers. Full article
(This article belongs to the Special Issue Impact of Large Wood on River Ecosystems)
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Article
Engineered Large Wood Structures in Stream Restoration Projects in Switzerland: Practice-Based Experiences
Water 2021, 13(18), 2520; https://doi.org/10.3390/w13182520 - 14 Sep 2021
Viewed by 992
Abstract
The effects of large wood (LW) presence in streams on river ecology and morphology are becoming widely researched and nowadays their ecological benefits are undisputed. Yet LW presence in most Swiss plateau streams is poor mainly due to anthropological pressure on river ecosystems. [...] Read more.
The effects of large wood (LW) presence in streams on river ecology and morphology are becoming widely researched and nowadays their ecological benefits are undisputed. Yet LW presence in most Swiss plateau streams is poor mainly due to anthropological pressure on river ecosystems. The use of anchored, engineered LW structures under various forms in stream restoration projects is now state of the art. However, binding benchmarks for the equivalent naturally occurring instream LW quantities and complex LW structures do not yet exist. Therefore, hydraulic engineers often find themselves in a conflict between acceptable instream LW quantities for flood protection, quantities desirable from an ecological point of view and, last but not least, quantities accepted by the public based on the current ideologies of landscape design. In the first section, this paper treats the complexity of defining benchmarks for LW quantities in restoration projects. In the second section, we provide a qualitative practical insight into relevant questions when planning engineered LW structures, such as placement, anchoring, naturalness, and effectiveness from a hydraulic engineer’s point of view. The third part presents three examples of restoration projects with different dimensions where various engineered LW structures with different outcomes were built and introduced into active streams. Finally, the conclusion provides further possible measures to retain LW in streams and to restore more natural LW dynamics in rivers. Full article
(This article belongs to the Special Issue Impact of Large Wood on River Ecosystems)
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Article
Field Study on Wood Accumulation at a Bridge Pier
Water 2021, 13(18), 2475; https://doi.org/10.3390/w13182475 - 09 Sep 2021
Viewed by 624
Abstract
Transported large wood (LW) in rivers may block at river infrastructures such as bridge piers and pose an additional flood hazard. An improved process understanding of LW accumulations at bridge piers is essential for a flood risk assessment. Therefore, we conducted a field [...] Read more.
Transported large wood (LW) in rivers may block at river infrastructures such as bridge piers and pose an additional flood hazard. An improved process understanding of LW accumulations at bridge piers is essential for a flood risk assessment. Therefore, we conducted a field study at the River Glatt in Zurich (Switzerland) to analyze the LW accumulation process of single logs at a circular bridge pier and to evaluate the results of previous flume experiments with respect to potential scale effects. The field test demonstrated that the LW accumulation process can be described by an impact, rotation, and separation phase. The LW accumulation was described by combining two simplified equilibria of acting forces and moments, which are mainly a function of the pier diameter, pier roughness, and flow properties. We applied the resulting analytic criterion to the field data and demonstrated that the criterion can explain the behavior of 82% of the logs. In general, the field observations confirmed previous results on the LW accumulation probability in the laboratory, which supports the applicability of laboratory studies to investigate LW–structure interactions. Full article
(This article belongs to the Special Issue Impact of Large Wood on River Ecosystems)
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Article
Wood Retention at Inclined Bar Screens: Effect of Wood Characteristics on Backwater Rise and Bedload Transport
Water 2021, 13(16), 2231; https://doi.org/10.3390/w13162231 - 16 Aug 2021
Viewed by 626
Abstract
In forested mountain catchment areas, both bedload and large wood (LW) can be transported during ordinary flows. Retention structures such as sediment traps or racks are built to mitigate potential hazards downstream. Up to now, the design of these retention structures focuses on [...] Read more.
In forested mountain catchment areas, both bedload and large wood (LW) can be transported during ordinary flows. Retention structures such as sediment traps or racks are built to mitigate potential hazards downstream. Up to now, the design of these retention structures focuses on either LW or bedload. In addition, the majority of LW retention racks tend to retain both LW and bedload, while bedload transport continuity during ordinary flows is an important aspect to be considered in the design. Therefore, a series of flume experiments was conducted to study the effect of LW accumulations at an inclined bar screen with a bottom clearance on backwater rise and bedload transport. The main focus was put on testing different LW characteristics such as LW size, density, fine material, and shape (branches and rootwads), as well as a sequenced flood. The results demonstrated that a few logs (wood volume of ≈ 7 m3 prototype scale with a model scale factor of 30) are sufficient to reduce the bedload transport capacity to below 75% compared to the condition without LW. Fine material and smaller wood sizes further reduced bedload transport and increased backwater rise. In contrast, LW density and LW shape had a negligible effect. The test focusing on a sequenced flood highlighted the need for maintenance measures to avoid self-flushing of the bed material. The results of this study further indicate that an inclined bar screen may need to be adapted by considering LW characteristics in the design of the bottom clearance to enable bedload continuity during ordinary flows. Full article
(This article belongs to the Special Issue Impact of Large Wood on River Ecosystems)
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Article
Flume Experiments Evaluating the Efficacy of a Large Wood Trap Featuring Horizontal Rods
Water 2021, 13(13), 1837; https://doi.org/10.3390/w13131837 - 30 Jun 2021
Viewed by 730
Abstract
Large wood (LW) disasters, which often accompany sediment-related disasters, occur worldwide. To prevent and mitigate such disasters, we developed a unique LW trap featuring horizontal rods aligned with the flow. When LW enters the trap, it is scooped up by the rods and [...] Read more.
Large wood (LW) disasters, which often accompany sediment-related disasters, occur worldwide. To prevent and mitigate such disasters, we developed a unique LW trap featuring horizontal rods aligned with the flow. When LW enters the trap, it is scooped up by the rods and thus separated from water and sediment. We explored trapping efficacy using a flume of slope 0.087. Water circulated at a constant rate of 1.8 L/s, LW was added to the flow, and the trapping rates were measured. We focused on the relative wood length (Lw) with respect to the horizontal rod spacing (Sr), the number of LW units supplied, and the supply rate. A longer relative length (Lw/Sr) of LW was associated with a higher trapping rate. The trapping rate was also high when the LW number or supply rate was high. The critical Lw/Sr value was 1.5; below this value, LW was not trapped. This study yields the basic information needed to design traps featuring horizontal rods to mitigate LW-related disasters. Full article
(This article belongs to the Special Issue Impact of Large Wood on River Ecosystems)
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