scholarly journals Flume Experiments Evaluating the Efficacy of a Large Wood Trap Featuring Horizontal Rods

Water ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 1837
Author(s):  
Mayuko Furukawa ◽  
Daizo Tsutsumi ◽  
Hironori Muto ◽  
Taro Uchida ◽  
Takuro Suzuki ◽  
...  
Keyword(s):  
Relative Length ◽  
Large Wood ◽  
Basic Information ◽  
Trapping Rate ◽  
Supply Rate ◽  
Flume Experiments ◽  
Water And Sediment ◽  
Constant Rate

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.

Flume experiments on the geomorphic effects of large wood in gravel-bed rivers

2020 ◽  
pp. 1609-1615
Author(s):  
D. Ravazzolo ◽  
G. Spreitzer ◽  
H. Friedrich ◽  
J. Tunnicliffe
Keyword(s):  
Large Wood ◽  
Flume Experiments ◽  
Gravel Bed ◽  
Gravel Bed Rivers

scholarly journals Hazards due to large wood accumulations: Local scour and backwater rise

2018 ◽  
Vol 40 ◽  
pp. 02003 ◽  
Author(s):  
Isabella Schalko ◽  
Lukas Schmocker ◽  
Volker Weitbrecht ◽  
Robert M. Boes
Keyword(s):  
Shear Stress ◽  
Flood Hazard ◽  
Local Scour ◽  
Bridge Piers ◽  
Bed Shear Stress ◽  
Large Wood ◽  
Flume Experiments ◽  
Governing Parameter ◽  
Bed Material ◽  
Movable Bed

Large wood (LW) in rivers increases the flow variability and provides habitats for various species. During flood events, transported logs can accumulate at river infrastructures and increase the flood hazard. LW accumulations result in an upstream backwater rise and may increase local scour, for instance at bridge piers. Consequently, estimates of the resulting backwater rise and local scour are necessary to improve the flood hazard assessment. This study presents the findings of flume experiments with a movable bed on local scour and backwater rise due to LW accumulations. The approach flow conditions and the bed material were varied systematically for a specific LW accumulation volume. For all experiments, the initial condition for the bed material was defined as weak transport, since the bed shear stress was slightly below the critical bed shear stress for incipient motion. The inflow Froude number was identified as the governing parameter for backwater rise due to LW accumulations. The present study confirms the hypothesis that the resulting local scour reduces backwater rise. For the local scour, the unit discharge and the grain size diameter are the decisive parameters.

scholarly journals Laboratory Flume Experiments on the Formation of Spanwise Large Wood Accumulations: Part II-Effect on local scour

2019 ◽  
Vol 55 (6) ◽  
pp. 4871-4885 ◽  
Author(s):  
I. Schalko ◽  
C. Lageder ◽  
L. Schmocker ◽  
V. Weitbrecht ◽  
R. M. Boes
Keyword(s):  
Local Scour ◽  
Large Wood ◽  
Flume Experiments ◽  
Laboratory Flume

scholarly journals Wood Retention at Inclined Bar Screens: Effect of Wood Characteristics on Backwater Rise and Bedload Transport

Water ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2231
Author(s):  
Isabella Schalko ◽  
Virginia Ruiz-Villanueva ◽  
Fiona Maager ◽  
Volker Weitbrecht
Keyword(s):  
Sediment Traps ◽  
Bedload Transport ◽  
Large Wood ◽  
Transport Capacity ◽  
Flume Experiments ◽  
Fine Material ◽  
Mountain Catchment ◽  
Catchment Areas ◽  
Bed Material ◽  
Retention Structures

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.

Drag coefficients of large instream wood – mystery or science?

2021 ◽  
Author(s):  
Ingo Schnauder
Keyword(s):  
Horizontal Cylinder ◽  
Large Wood ◽  
Flume Experiments ◽  
Cross Sectional ◽  
Drag Coefficients ◽  
Free Stream Turbulence ◽  
First Results ◽  
Channel Aspect Ratio ◽  
3D Effects ◽  
Energy And Momentum

<p>Drag coefficients convert flow velocity into the force exerted on a body and hydraulic head loss. They spatially integrate all properties of a given configuration into one single parameter. Therefore, drag coefficients are widely used in engineering, including environmental flow applications such as large wood log. However, the scatter in drag coefficients reported from previous studies clearly indicate that universality is no longer given and predictions underlie large uncertainties. Deeper analyses are mostly restricted due to insufficient hydraulic data – which in many studies is simply the discharge and the derived cross-sectionally averaged velocity.</p><p>It is obvious, that the ‘ideal’ drag coefficients from infinite and low-turbulence wind tunnel studies with the iconic c<sub>D</sub> = 1.1 for the subcritical regime (10<sup>4</sup> < Re < 10<sup>5</sup>) do not apply anymore. Instead, disturbances play a major role. For large wood, these are typically (i) blockage of the finite river cross-sectional area, (ii) the proximities of the bed below and the free-surface above, (iii) interaction with the free-stream turbulence, (iv) wake interference and (v) 3D-effects such as free ends of the cylindrical or channel aspect ratio.</p><p>To search for a more robust predictive scheme, we started flume experiments with horizontal cylinder configurations and measured the flow field in vertical profiles as well as the overall drag. First results shifted our emphasis from drag to velocity coefficients like the ones used in energy and momentum equations to account for non-uniformity. This seems reasonable, both because of the the squared represention of velocity in the drag term and because of the significant non-uniformities in large wood constellations.</p>

scholarly journals Large wood transport and jam formation in a series of flume experiments

2015 ◽  
Vol 51 (12) ◽  
pp. 10065-10077 ◽  
Author(s):  
S. L. Davidson ◽  
L. G. MacKenzie ◽  
B.C. Eaton
Keyword(s):  
Large Wood ◽  
Flume Experiments ◽  
Large Wood Transport ◽  
Wood Transport

scholarly journals A One-Way Coupled Hydrodynamic Advection-Diffusion Model to Simulate Congested Large Wood Transport

Hydrology ◽  
2021 ◽  
Vol 8 (1) ◽  
pp. 21
Author(s):  
Elisabetta Persi ◽  
Gabriella Petaccia ◽  
Stefano Sibilla ◽  
Roberto Bentivoglio ◽  
Aronne Armanini
Keyword(s):  
Diffusion Model ◽  
Large Wood ◽  
Flume Experiments ◽  
Longitudinal Diffusion ◽  
Advection Diffusion Equation ◽  
Advection Diffusion ◽  
Proposed Model ◽  
Coupled Solution ◽  
Large Wood Transport ◽  
Wood Transport

An advection-diffusion model is proposed to simulate large wood transport during high flows. The mathematical model is derived from the wood mass balance, taking into consideration both the wood mass concentration and the log orientation, which affects log transport and, most importantly, wood accumulation. Focusing on wood mass transport, the advection-diffusion equation is implemented in a hydrodynamic model to provide a one-way coupled solution of the flow and of the floating wood mass. The model is tested on a large series of flume experiments, involving at least 30 logs and different control parameters (flow Froude number, log length, diameter, release point). The validation through the experimental data shows that the proposed model can predict the correct displacement of the most probable position of the logs and to simulate with a sufficient accuracy the planar diffusion of the wooden mass. Transversal wood distribution is more accurate than the streamwise one, indicating that a higher control on the longitudinal diffusion needs to be implemented.

The effects of large wood (LW) on water and sediment connectivity in river systems: a new LW dis-connectivity index and its application in sediment management contexts

2021 ◽  
Author(s):  
Ronald E. Pöppl ◽  
Hannah Fergg ◽  
Maria T. Wurster ◽  
Anne Schuchardt ◽  
David Morche
Keyword(s):  
Sediment Management ◽  
Connectivity Index ◽  
Large Wood ◽  
Transport Capacity ◽  
Water And Sediment ◽  
Channel Blockage ◽  
Sediment Connectivity ◽  
Channel Hydraulics ◽  
The Relationship ◽  
Mixed Load

<p>It is well known that in-stream large wood (LW) can have significant effects on channel hydraulics and thus water and sediment connectivity, i.e. by creating hydraulic resistance that decreases flow velocity and transport capacity. The relationship between an in-stream LW structure and its hydraulic function (incl. the related effects on water and sediment connectivity) is generally quantified through drag force. Drag analyses, however, are data-demanding and often not straightforward - especially in complex debris jam settings where LW accumulations consist of wood pieces of widely variable sizes. Here, we introduce a simple LW dis-connectivity index (calculated based on visually estimated, field-derived LW parameters such as the degree of channel blockage), which has been applied in different sediment management contexts in medium-sized mixed-load streams in Austria.</p><p> </p>

Large wood hydraulics - a fluvial process of growing interest

2020 ◽  
Author(s):  
Ingo Schnauder
Keyword(s):  
River Restoration ◽  
Research Programme ◽  
Field Measurements ◽  
Large Wood ◽  
Interference Field ◽  
Flume Experiments ◽  
Fluvial Process ◽  
Wake Interference ◽  
Lab Experiments ◽  
Flow Morphology

<p>In the last decade, the perception of large wood in rivers has shifted from a hazard perspective towards a valuable and required component of the river ecosystem. Consequently, there is a demand to quantify and predict the effects of large wood on flow, morphology and retention.</p><p>The research programme ‘Large Wood Hydraulics’ investigates the flow and turbulence characteristics of instream large wood. Within the programme, field measurements and lab experiments are conducted and cover different wood types (tree morphology, branching pattern), their position / orientation in the cross-section and single or multiple elements (wake interference). Field measurements were carried out in river Mulde, Germany within the BMBF-project ‘Wilde Mulde’ and flume experiments in the hydraulics lab of  TU Vienna.</p><p>The aim of the study is to predict the effects of different wood configurations to promote the use of wood in river restoration schemes.</p>

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