Experimental analysis of open check dams and protection bars against debris flows and driftwood

Rossi, Giulia; Armanini, Aronne

doi:10.1007/s10652-019-09714-9

Cited by 20 publications

(20 citation statements)

References 16 publications

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“…Acknowledging that LW recruitment and transfer is quite random in the field (Comiti et al, 2016), we did not try to define a relevant rate of LW introduction in the flume as done in other works (e.g. D'Agostino et al, 2000;Meninno et al, 2019;or Rossi and Armanini, 2019). Rather, an inverse approach was chosen of trying to supply LW to make the jam "supply unlimited".…”

Section: Experimental Protocolmentioning

confidence: 99%

“…These works have mostly focused on trapping efficacy and on defining relevant opening sizes and shapes to achieve the desired function. Numerical modelling of LW freely floating or interacting with structures emerged in the 2010s and is subject to constant improvement (Horiguchi et al, 2015;Kimura and Kitazono, 2019;Ruiz-Villanueva et al, 2014a;Shrestha et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

“…Recent experiments by Rossi and Armanini 2019, Meninno et al (2019), and Chen et al (2020) also explored the trapping efficacy of slits dams, without and eventually with upstream grills as suggested by Bezzola et al (2004). Experiments on racks and slit dams did not address the question of LW overtopping because the modelled structures were not overtopped (D'Agostino et al, 2000;Schmocker and Hager, 2013;Schmocker and Weitbrecht, 2013;Schmocker et al, 2014;Schalko et al, 2018Schalko et al, , 2019aRossi and Armanini, 2019;Meninno et al, 2019;Chen et al, 2020). The authors merely reported high trapping efficacy (> 90 %) for the tested racks and that trapping efficacy varies with slit width and the interval between upstream grill bars.…”

Section: Introductionmentioning

confidence: 99%

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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: Experimental Protocolmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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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“…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%

“…Rossi and Armanini [27] analyse the efficiency of different protection structures (slit check dams, either alone or equipped with steel ramps) in mountain steep streams characterized by intense phenomena of driftwood and bed load/debris flow. Several different parameters are defined to evaluate these structural measures, namely the percentage of trapped driftwood, the clogging tie for driftwood and sediment, the driftwood trapping efficiency.…”

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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Wood retention at inclined racks: Effects on flow and local bedload processes

Schalko

2020

Earth Surf Processes Landf

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Large wood (LW) transport can increase greatly during floods, leading to accumulations at river infrastructures. To mitigate the potential flood hazard, racks are a common method to retain LW upstream of endangered settlements or infrastructures. The majority of LW retention racks consist of vertical bars and, therefore, disrupt bedload transport. It can be hypothesized that inclined racks reduce backwater rise and local scour, as wood will block the upper part of the rack, thereby increasing the open flow cross‐section below the accumulation. Flume experiments were conducted under clear water conditions to analyse backwater rise and local scour as a function of (1) rack inclination, (2) hydraulic inflow condition, (3) uniform bed material, and (4) LW volume. In addition, the first experiments were performed under live bed scour conditions to study the effect of bedload transport on local scour and backwater rise. Based on the experiments, backwater rise and local scour decrease with decreasing rack angle to the horizontal. LW predominantly accumulated at the upper part of the rack, leading to an open flow cross‐section below the accumulation. The effect of rack angle was included in existing design equations for backwater rise and local scour depth. In addition, the first experiments with bedload transport resulted in smaller backwater rise and local scour depth. This study contributes to an enhanced process understanding of wood retention and bedload transport at rack structures and an improved design of LW retention racks. © 2020 John Wiley & Sons, Ltd.

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Experimental analysis of open check dams and protection bars against debris flows and driftwood

Cited by 20 publications

References 16 publications

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

Wood retention at inclined racks: Effects on flow and local bedload processes

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