Flow, turbulence, and drag associated with engineered log jams in a fixed-bed experimental channel

Bennett, Sean J.; Ghaneeizad, Seyed Mohammad; Gallisdorfer, Michael S.; Cai, De; Atkinson, Joseph F.; Simon, Andrew; Langendoen, Eddy J.

doi:10.1016/j.geomorph.2015.07.046

Cited by 31 publications

(28 citation statements)

References 42 publications

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“…For the fully-resolved case, which serves as the baseline for the evaluation of the other two simplifications, we found that the turbulent inlet condition was critical for better comparison with the experiments in Bennett et al [10]. In this study, a background case without ELJ was first run to get a fully-developed open channel flow, which was then used at the inlet.…”

Section: Validation Of the Fully-resolved Configurationmentioning

confidence: 99%

“…In this study, the ELJ flume experiments in [10,30] were simulated and analyzed. The water depth was H = 114 mm, and the flume width was B = 1900 mm.…”

Section: Geometry Preparation and Mesh Generationmentioning

confidence: 99%

“…The channel outlet was set as a far field, and no back flow was allowed. The inlet boundary condition is more difficult to impose in order to reproduce the physical experiment in Bennett et al [10]. The mean velocity of the incoming flow was u 0 ≈ 0.124 m/s.…”

Section: Boundary Conditionsmentioning

confidence: 99%

“…Recognizing their importance to rivers, in-stream structures have been widely used in stream restoration projects [8]. Examples of these structures include single log vane, log cross vane, mud sill, multi-log vane deflector, water jack and engineered log jams (ELJ) [9], among which ELJ is a very attractive option due to its abundant eco-hydraulic benefits [10].…”

Section: Introductionmentioning

confidence: 99%

“…The three geometric representations include the fully-resolved model (no simplification in geometry), the porosity model and solid barrier (i.e., treating the ELJ as an impervious box). The simulation case was based on the flume experiments for ELJ in [10,30]. In the following, the computational models will be introduced first.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Different In-Stream Structure Representations in Computational Fluid Dynamics Models—Taking Engineered Log Jams (ELJ) as an Example

Liu

2017

Water

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Abstract:In-stream structures contribute greatly to the biodiversity in streams and play an important role in restoring and protecting rivers. They usually have complex geometries. To evaluate their impact and effectiveness, computational models are increasingly used. However, how to faithfully represent them in computer models remains a challenge. Often, simplifications have to be made. This work evaluated the effects of geometric simplification of an example in-stream structure, an engineered log jam (ELJ), in computational models. Three different representations were considered, namely full resolution, the porous media model and the solid barrier model. The turbulent flow was resolved with large eddy simulation (LES). First, the simulations were validated with a physical experiment in a flume. Then, the results from the three models were compared and analyzed on various aspects related to the stability and functionalities of the structures. Unsurprisingly, it is found that the porous media model and the solid barrier model, which are computationally economic, can describe the flow dynamics only to some extent. From the calibration of drag force and wake length, we found that the equivalent grain size d 50 in the porosity model should scale as the key element diameter for the simulated ELJ. A wake length scale analysis was performed for the semi-bounded flow around this in-stream structure near the bank. The length estimator in the literature for unbounded vegetation patches can be used with modifications. The results also show that the flow passing through the porous in-stream structure has a significant impact on mean velocity, turbulence kinetic energy, sediment transport capacity and integral wake length. Since geometrically-fully-resolved simulations are not currently feasible for engineering practices, the following suggestions are made based on this study. If the near-field and wake are important for the purpose of the structure, the well-calibrated porosity model seems to perform better than the solid barrier model. However, care needs to be taken when interpreting the results because this work also identified substantial loss of physical information with the porosity model. When the emphasis is the far field away from the structure, both the porosity model and the solid barrier model give comparable results.

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Section: Validation Of the Fully-resolved Configurationmentioning

confidence: 99%

“…In this study, the ELJ flume experiments in [10,30] were simulated and analyzed. The water depth was H = 114 mm, and the flume width was B = 1900 mm.…”

Section: Geometry Preparation and Mesh Generationmentioning

confidence: 99%

Section: Boundary Conditionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Effects of Different In-Stream Structure Representations in Computational Fluid Dynamics Models—Taking Engineered Log Jams (ELJ) as an Example

Liu

2017

Water

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Untangling the controls on bedload transport in a wood‐loaded river with RFID tracers and linear mixed modelling

Clark

Bennett

Ryan-Burkett

et al. 2022

Earth Surf Processes Landf

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Bedload transport is a fundamental process by which coarse sediment is transferred through landscapes by river networks and may be well described stochastically by distributions of grain step length and rest time obtained through tracer studies. To date, none of these published tracer studies have specifically investigated the influence of large wood in the river channel on sediment transport dynamics, limiting the applicability of stochastic sediment transport models in these settings. Large wood is a major component of many forested rivers and is increasing due to anthropogenic ‘Natural Flood Management’ (NFM) practices. This study aims to investigate and model the influence of large wood on grain‐scale bedload transport. We tagged 957 cobble to pebble sized particles (D50 = 73 mm) and 28 pieces of large wood (> 1 m in length) with radio frequency identification (RFID) tracers in an alpine mountain stream. We monitored the transport distance of tracers annually over 3 years, building distributions of tracer transport distances with which to compare with published distributions from wood free settings. We also applied linear mixed modelling (LMM), to tease out the influence of wood from other controls on likelihood of entrainment, deposition, and the transport distances of sediments. Tracer sediments accumulated both upstream and downstream of large wood pieces, with LMM analysis confirming a reduction in the probability of entrainment of tracers closer to wood in all 3 years. Upon remobilization, tracers entrained from positions closer to large wood had shorter subsequent transport distances in each year. In 2019, large wood also had a trapping effect, significantly reducing the transport distances of tracer particles entrained from upstream, that is forcing premature deposition of tracers. This study demonstrates the role of large wood in influencing bedload transport in alpine stream environments, with implications for both natural and anthropogenic addition of wood debris in fluvial environments.

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Effects of an engineered log jam on spatial variability of the flow field across submergence depths

L'Hommedieu¹,

Tullos

Jones

2020

River Research & Apps

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Engineered log jams (ELJs) are commonly implemented in rivers to diversify fish habitat, but few studies have verified the hydraulic benefits of ELJs by assessing their effects on the spatial variability and turbulence structure of the flow field. This field and modelling study assessed the effects of an ELJ on various characteristics of the flow field with increasing submergence. A 2‐D hydrodynamic model was applied to simulate flow conditions of the Calapooia River, Oregon, with an ELJ installed at the upstream end of a meander. Output was analyzed using coherent flow structure identification, maps of turbulence measures, and wavelet analysis along linear transects. At the highest discharge (62% ELJ submergence), more and smaller coherent flow structures were identified than in the no ELJ model run, but the magnitudes of turbulence metrics were unaffected. At low flow (1% jam submergence), the presence of the ELJ did not affect the number of coherent flow structures identified and produced only small and localized effects on turbulence measures. Taken together, results indicate that the ELJ primarily affected the flow field by increasing the number of flow structures at higher discharges and submergence depths. However, these changes were small and local to the ELJ. The limited effects of this wood jam over limited spatial scales raise questions about the conditions under which such structures increase hydraulic diversity and highlight the need for more detailed understanding on spatial variability around habitat structures with complex shapes.

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Flow, turbulence, and drag associated with engineered log jams in a fixed-bed experimental channel

Cited by 31 publications

References 42 publications

Effects of Different In-Stream Structure Representations in Computational Fluid Dynamics Models—Taking Engineered Log Jams (ELJ) as an Example

Effects of Different In-Stream Structure Representations in Computational Fluid Dynamics Models—Taking Engineered Log Jams (ELJ) as an Example

Untangling the controls on bedload transport in a wood‐loaded river with RFID tracers and linear mixed modelling

Effects of an engineered log jam on spatial variability of the flow field across submergence depths

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