Reduction of Bend Scour by an Outer Bank Footing: Footing Design and Bed Topography

Roca, Marta; Vide, Juan Pedro Martín; Blanckaert, Koen

doi:10.1061/(asce)0733-9429(2007)133:2(139)

Cited by 35 publications

(17 citation statements)

References 11 publications

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“…Figure 2 illustrates the morphology in the three experiments. The flume-averaged bed level defines the reference level, z = 0 m. The live-bed (LB_NB) and clear-water scour (CW_NB) experiments without bubble screen are characterized by similar morphological features that are typical for sharply curved open-channel bends (Roca et al, 2007;Blanckaert, 2010): a bar-pool morphology with two deep scour holes located near the entry and the exit of the bend, respectively, and a depositional bar at the inner bank between the cross sections located at 30° and 150° in the bend. The maximum scour depth in both experiments is similar and about 0.25 m under the flume-averaged bed level.…”

Section: Experimental Conditionsmentioning

confidence: 99%

“…Several techniques exist to reduce these adverse impacts, but they generally imply substantial constructive works. Techniques reported in literature include bottom vanes (Odgaard and Spoljaric, 1986;Odgaard and Wang, 1991), fixed layers (Roca et al, 2007), submerged groynes (Przedwojski, 1995) and bandal-like structures (Teraguchi et al, 2011). However, these techniques have the disadvantage of being fixed constructions on the bed that represent a possible threat for navigation.…”

Section: Introductionmentioning

confidence: 99%

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Reduction of bend scour with an air-bubble screen – morphology and flow patterns

Dugué

Blanckaert

Chen

et al. 2013

International Journal of Sediment Research

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The interplay between streamwise flow, curvature-induced secondary flow, sediment transport and bed morphology leads to the formation of a typical bar-pool bed morphology in open-channel bends. The associated scour at the outer bank and deposition at the inner bank may endanger the outer bank's stability or reduce the navigable width of the channel. Previous preliminary laboratory experiments in a sharply curved flume with a fixed horizontal bed have shown that a bubble screen located near the outer bank can generate an additional secondary flow located between the outer bank and the curvature-induced secondary flow and with a sense of rotation opposite to the latter. This bubble-induced secondary flow redistributes velocities and bed shear stresses. The reported study investigates the implications of a bubble screen on the flow and the morphology in configurations with mobile bed. Velocity measurements show that the bubble-induced secondary flow shifts the curvature-induced secondary flow in inwards direction and reduces its strength. The bubble screen considerably reduces morphological gradients. Maximum bend scour is reduced by about 50% and occurs further away from the outer bank where it does not endanger the bank stability anymore. The location of maximum scour coincides with the junction of the curvature-induced and bubble-induced secondary flows. At this same location, the maximum streamwise velocities and maximum vertical velocities impinging on the bed also occur, which indicates their importance with respect to the formation of bend scour. The bubble screen also substantially reduced deposition at the inner bank. These preliminary experiments show the potential of a bubble screen to influence and modify the bed morphology.

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Section: Experimental Conditionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Reduction of bend scour with an air-bubble screen – morphology and flow patterns

Dugué

Blanckaert

Chen

et al. 2013

International Journal of Sediment Research

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“…Pagliara and Palermo (2008) and Pagliara et al (2009) studied the effect of protection sills in the stilling basin for different bed materials on the scour morphology downstream of block ramps. Roca et al (2007Roca et al ( , 2009 showed that a well-designed horizontal foundation of the outer river bend, called footing, could protect vertical outer banks against erosion reducing the scour depth. Bhuiyan et al (2007) studied the scour development downstream of W-weir at river bends in clear water and live-bed conditions.…”

Section: Introductionmentioning

confidence: 99%

Clear water scour at J-Hook Vanes in channel bends for stream restorations

Pagliara

Kurdistani

2015

Ecological Engineering

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“…Such measures include either changing the flow patterns directly or protecting the riverbed. Examples of erosion preventing measures are utilization of riprap (Martin-Vide et al 2010); undulated, macrorough riprap (Chèvre and Schleiss 2005); installation of bottom vanes (Odgaard and Spoljaric 1986;Odgaard and Wang 1991;Voisin and Townsend 2002) or bank-attached vanes (Bhuiyan et al 2010); lining of the outer bank with concrete slabs (Sloff et al 2006;Roca et al 2007); construction of groynes or spur dikes (Przedwojski 1995;Sukhodolov et al 2002;Jamieson et al 2013b, a); construction of bendway weirs (Abad et al 2008); and construction of bandal-like structures (Teraguchi et al 2011). Blanckaert et al (2010Blanckaert et al ( , 2012 studied the influence of roughness at the outer bank in two distinct situations in a laboratory 193°channel bend (Blanckaert 2002), a rectangular channel, and a trapezoidal channel with 30°-inclined outer bank.…”

Section: Introductionmentioning

confidence: 99%

Wall-Roughness Effects on Flow and Scouring in Curved Channels with Gravel Beds

2016

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Due to a complex three-dimensional flow pattern, the outer banks of river bends are predisposed to erosion. When endangering civil structures, preventing measures to mitigate this erosion are thus required. Vertical ribs at protection walls for scour reduction have been applied to several flood protection projects in mountain rivers; nevertheless, no systematic and intensive study has been presented so far to evaluate their effect. This paper investigates experimentally the effect of vertical ribs, placed as macroroughness elements on the outer vertical wall of a 90°laboratory channel bend. Systematic tests were performed using a wide and coarse grain-size distribution. Scour formation and velocity distribution were assessed in the channel in the presence of a macrorough outer bank, materialized in the laboratory by vertical elements placed on the outer vertical wall along the channel bend. Experiments showed that the macrorough outer bank changed considerably the bed morphology under equilibrium conditions. Maximum scour depth is considerably reduced by the vertical ribs placed at an optimal spacing on the bend outer wall. A considerable grain sorting process occurs across the cross section in the bend, which influences the scour process; differences are observed between situations with and without macrorough banks. The distribution of the time-averaged velocity field across the section shows the influence of the channel rough wall. An optimal macroroughness configuration in terms of scour reduction is discussed and proposed. It was observed that when spacing between vertical ribs is too reduced, these ribs act as uniformly distributed wall roughness, contributing to the width reduction due to the occupation of the cross section and increasing consequently the flow velocity with negative effects in scour reduction.

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Reduction of Bend Scour by an Outer Bank Footing: Footing Design and Bed Topography

Cited by 35 publications

References 11 publications

Reduction of bend scour with an air-bubble screen – morphology and flow patterns

Reduction of bend scour with an air-bubble screen – morphology and flow patterns

Clear water scour at J-Hook Vanes in channel bends for stream restorations

Wall-Roughness Effects on Flow and Scouring in Curved Channels with Gravel Beds

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