Coupling check dams with large wood retention structures in clean water

Meninno, Sabrina; Canelas, Ricardo B.; Cardoso, António H.

doi:10.1007/s10652-019-09711-y

Cited by 17 publications

(14 citation statements)

References 20 publications

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“…where C D is the drag coefficient (-) assumed to be equal to 1.2 for logs without branches (Merten et al, 2010;Ruiz-Villanueva et al, 2014a) and v is the flow velocity near the log (m s −1 ). This formulation relies on several hypotheses: (i) the log is assumed to be in a transverse position with respect to the flow direction and quasi-submerged, consistent with the hypothesis made for buoyancy, and the surface of the log is proportional to its diameter times its length; (ii) the log is quasi-immobile, so the full velocity of the flow is considered; (iii) the precise value of v in the direct vicinity of the logs is unknown, but the cross-sectional-averaged velocity is considered relevant as a first approximation; thus v ≈ Q/(hW ) where W is the flume width (here 0.4 m).…”

Section: Release Conditionsmentioning

confidence: 99%

Open check dams and large wood: head losses and release conditions

Piton¹,

Horiguchi²,

Marchal³

et al. 2020

Nat. Hazards Earth Syst. Sci.

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Abstract. Open check dams are strategic structures to control sediment and large-wood transport during extreme flood events in steep streams and piedmont rivers. Large wood (LW) tends to accumulate at such structures, obstruct their openings and increase energy head losses, thus increasing flow levels. The extent and variability to which the stage–discharge relationship of a check dam is modified by LW presence has so far not been clear. In addition, sufficiently high flows may trigger a sudden release of the trapped LW with eventual dramatic consequences downstream. This paper provides experimental quantification of LW-related energy head loss and simple ways to compute the related increase in water depth at dams of various shapes: trapezoidal, slit, slot and sabo (i.e. made of piles), with consideration of the flow capacity through their open bodies and atop their spillways. In addition, it was observed that LW is often released over the structure when the overflowing depth, i.e. total depth minus spillway elevation, is about 3–5 times the mean log diameter. Two regimes of LW accumulations were observed. Dams with low permeability generate low velocity upstream, and LW then accumulates as floating carpets, i.e. as a single floating layer. Conversely, dams with high permeability maintain high velocities immediately upstream of the dams and LW tends to accumulate in dense complex 3D patterns. This is because the drag forces are stronger than the buoyancy, allowing the logs to be sucked below the flow surface. In such cases, LW releases occur for higher overflowing depth and the LW-related head losses are higher. A new dimensionless number, namely the buoyancy-to-drag-force ratio, can be used to compute whether (or not) flows stay in the floating-carpet domain where buoyancy prevails over drag force.

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Section: Release Conditionsmentioning

confidence: 99%

Open check dams and large wood: head losses and release conditions

Piton¹,

Horiguchi²,

Marchal³

et al. 2020

Nat. Hazards Earth Syst. Sci.

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show abstract

“…It was also recently thoroughly covered by the hydraulic research team of ETH Zürich for rack structures made of piles (Schalko et al, 2018(Schalko et al, , 2019a(Schalko et al, , 2019bSchmocker and Hager, 2013;Schmocker and Weitbrecht, 2013;Schmocker et al, 2014). Recent experiments by Rossi and Armanini (2019), Meninno et al (2019) and Chen et al (2020) also explored trapping efficacy of slits dams, without and eventually with upstream grills as suggested by Bezzola et al (2004). All these works describe comprehensively how LW accumulates against barriers.…”

Section: In Particular Reportedmentioning

confidence: 99%

“…The ratio of LW length to pile interval was also known from SABO and slit dam experiments (Ishikawa and Mizuyama, 1989, Horiguchi et al, 2015, Chen et al 2020. Works on racks and slit dams did not address the question of LW overtopping because the modelled structure were not overtopped (Schmocker and Hager, 2013;Schmocker and Weitbrecht, 2013;Schmocker et al, 2014, Schalko et al, 2018, Rossi and Armanini 2019, Meninno et al, 2019, Chen et al, 2020 Since water depth above the structure seems a key driver of both sediment trapping and LW release, this paper seeks first to provide a way to compute water depth at structures in presence of LW, and secondly to study conditions driving the release of the trapped elements. This paper explores both questions experimentally.…”

Section: In Particular Reportedmentioning

confidence: 99%

Open check dams and large wood: head losses and release conditions

Piton¹,

Horiguchi²,

Marchal³

et al. 2020

Preprint

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Abstract. Open check dams are strategic structures to control sediment and large wood transport during extreme flood events in steep streams and piedmont rivers. Large wood (LW) tends to accumulate against such structures, to obstruct their openings and to increase energy dissipation and thus, flow levels. To which extent open check dams' stage-discharge relationships are consequently modified by LW presence was not clear so far. This question is key (i) to estimate how much bedload transport might be trapped in the related backwater areas and (ii) to estimate how high is the overflowing depth atop the structure. These flows, when sufficiently high, might trigger a sudden release of the previously trapped LW with eventual dramatic consequences downstream. This paper provides experimental quantification of LW-related energy dissipation and simple ways to compute the related increase in water depth at dams of various shapes: trapezoidal, slit, slot and SABO (i.e., made of piles), including flow capacity through their open body and atop the spillway. It was additionally observed that LW is often released over the structure when the overflowing depth, i.e., depth above the spillway, is about 3–5 the mean log diameter. Two regimes of LW accumulations were observed: dams with low permeability generate low velocity upstream and LW then accumulates as floating carpets, i.e., as a floating single layer. Conversely, dams with high permeability maintain high velocities close to the dams and LW tends to jam them in dense complex 3D patterns because drag forces are stronger than buoyancy and logs are sucked below the flow surface. In such cases, LW releases occur for higher overflowing depth and LW-related head losses are higher. A new dimensionless number, namely the ratio buoyancy to drag force, enables to compute whether or not flows stay in the floating carpet domain where buoyancy prevails.

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“…The topics dealt with in the papers range from the development and validation of numerical models to describe the interaction between flow and driftwood [11,17,21,23] to the experimental assessment of the Large Wood blocking at inline structures [14,20,27,31], to the evaluation of the stability of riparian vegetation during flood events and its consequent entrainment in the flow [12].…”

mentioning

confidence: 99%

“…Meninno et al [20] focus on the interaction between in-stream transported wood and check dams, through an experimental evaluation of the performance of rakes built upstream of slit check dams in clear water conditions. The backwater effect and the trapping efficiency of the wood retaining device are coupled to the different geometries and wood inputs, also including as reference the functioning of the check dam without any rack.…”

mentioning

confidence: 99%

Recent developments in the analysis of Large Wood dynamics in fluvial systems

Sibilla

Meninno²,

Canelas

2020

Environ Fluid Mech

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Wood in river plays a significant role in river geomorphology and ecology, by interacting with erosion and sedimentation processes, influencing the nutrients budget and providing physical habitats for a variety of species. However, Large Wood elements (LW, with a trunk diameter > 0.1 cm and a length > 1 m, as defined by Wohl et al. [38] transported during floods can aggravate the expected drawbacks and augment the overall risk at which the urban areas are exposed [7,8,28].LW may cause obstructions along the channel network, mostly in correspondence of bridges or weirs, where it accumulates, clogging the openings and causing a backwater rise upstream. Hydraulic structures can collapse as a result of the increased loads, and unexpected overflowing can occur at the jammed river cross-sections.The formation of LW accumulation is thus a key issue in the hydraulic risk assessment and its mechanism, as well its subsequent modelling, is still object of study [1,10,13,15,32,34]. It is highly affected by the interactions between water, sediments and structures, and it is also influenced by the physical features of LW element and river morphology [30].Due to the potential implications of LW during floods, different types of practical measures have been developed and employed [2, 5] to retain LW upstream of the critical sections (e.g. fins and racks, [26,33] or to reduce its presence in the river. These measures remain highly linked to the expertise of single practitioners, although recent works have proposed physically based designs of safety structures [25] both in mountain streams and low-land rivers.The need of giving a quantitative prediction of wood transport during floods throughout the river network has led researchers to investigate water-wood interactions both at a laboratory scale [3,4,6,9] and through numerical models [19,29]. The motion of floating wood on the water surface has been modelled with different strategies [22,28,35], mostly based on Eulerian-Lagrangian approaches able to trace wood motion and rotation.As an input, the aforementioned models require the volume and distribution of the wood that can be transported by the flood, and these data are affected by high uncertainty and derived through wood budget at basin scale [16,37]. In fact, wood entrained in a river can

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Coupling check dams with large wood retention structures in clean water

Cited by 17 publications

References 20 publications

Open check dams and large wood: head losses and release conditions

Open check dams and large wood: head losses and release conditions

Open check dams and large wood: head losses and release conditions

Recent developments in the analysis of Large Wood dynamics in fluvial systems

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