Observations on flow and local scour around submerged flexible vegetation

Chen, Su‐Chin; Chan, Hsun-Chuan; Li, Yu-Hsiu

doi:10.1016/j.advwatres.2012.03.017

Cited by 44 publications

(37 citation statements)

References 32 publications

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“…Many seagrass meadows can therefore be separated into two zones, based on the distance x from the front of the meadow (Fig. ): an erosive zone where the shoot‐scale turbulence promotes erosion ( x ≤ L D ), and a depositional zone where the reduction in current velocities overcomes the shoot‐scale turbulence to promote deposition ( x

\underset{>}{true}

L D ) (consistent with the observations of Bouma et al ; Chen et al ).…”

Section: Overview Of the Seagrass‐sediment‐light Feedbacksupporting

confidence: 79%

“…Hence, seagrass meadows of reduced length L and lower shoot density ( L / L D

\sim O (1)

) are more likely to enhance erosion, while longer meadows with higher shoot density ( L / L D >>

O (1)

) are more likely to be net depositional. This conceptual model is supported by laboratory studies that reported an increase in erosion associated with the presence of seagrass (Chen et al ; Follett and Nepf ; Ortiz et al ); in all of these studies, L / L D was

O (1)

. In the erosive zone, the volume of sediment eroded increases with flow velocity, plant size (Bouma et al ) and shoot density (Lawson et al ), all of which serve to increase the intensity of near‐bed turbulence.…”

Section: Overview Of the Seagrass‐sediment‐light Feedbackmentioning

confidence: 67%

“… (a) Reduction in near‐bed velocity occurs over the drag length scale L D , which defines the transition of the meadow from a net erosive zone to a net depositional zone. (b) A laboratory canopy showing the net erosive and depositional zones (modified from Chen et al ); the orange arrow represents the initial sediment bed height.…”

Section: Overview Of the Seagrass‐sediment‐light Feedbackmentioning

confidence: 99%

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Feedback between sediment and light for seagrass: Where is it important?

et al. 2016

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A feedback between seagrass presence, suspended sediment and benthic light can induce bistability between two ecosystem states: one where the presence of seagrass reduces suspended sediment concentrations to increase benthic light availability thereby favoring growth, and another where seagrass absence increases turbidity thereby reducing growth. This literature review identifies (1) how the environmental and seagrass meadow characteristics influence the strength and direction (stabilizing or destabilizing) of the seagrass-sediment-light feedback, and (2) how this feedback has been incorporated in ecosystem models proposed to support environmental decision making. Large, dense seagrass meadows in shallow subtidal, noneutrophic systems, growing in sediments of mixed grain size and subject to higher velocity flows, have the greatest potential to generate bistability via the seagrass-sediment-light feedback. Conversely, seagrass meadows of low density, area and height can enhance turbulent flows that interact with the seabed, causing water clarity to decline. Using a published field experiment as a case study, we show that the seagrass-sedimentlight feedback can induce bistability only if the suspended sediment has sufficient light attenuation properties. The seagrass-sediment-light feedback has been considered in very few ecosystem models. These models have the potential to identify areas where bistability occurs, which is information that can assist in spatial prioritization of conservation and restoration efforts. In areas where seagrass is present and bistability is predicted, recovery may be difficult once this seagrass is lost. Conversely, bare areas where seagrass presence is predicted (without bistability) may be better targets for seagrass restoration than bare areas where bistability is predicted.

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\underset{>}{true}

L D ) (consistent with the observations of Bouma et al ; Chen et al ).…”

Section: Overview Of the Seagrass‐sediment‐light Feedbacksupporting

confidence: 79%

“…Hence, seagrass meadows of reduced length L and lower shoot density ( L / L D

\sim O (1)

) are more likely to enhance erosion, while longer meadows with higher shoot density ( L / L D >>

O (1)

O (1)

Section: Overview Of the Seagrass‐sediment‐light Feedbackmentioning

confidence: 67%

Section: Overview Of the Seagrass‐sediment‐light Feedbackmentioning

confidence: 99%

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Feedback between sediment and light for seagrass: Where is it important?

et al. 2016

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“…This can also be beneficial for fluvial ecosystems [20]. Chen et al [21] conducted a set of flume experiments, with submerged instream vegetation of different densities, to assess the change in flow hydrodynamics, including velocity and turbulence, and the impact on local scouring around vegetation elements. A series of controlled flume experiments at the St Anthony Falls Laboratory (SAFL) outdoor stream facility, identified that plants' morphological characteristics, such as plant height and patch density, affect their probability of burial or uprooting and are important for their survival [22].…”

Section: Introductionmentioning

confidence: 99%

Flow Hydrodynamics across Open Channel Flows with Riparian Zones: Implications for Riverbank Stability

Valyrakis

Williams

2017

Water

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Riverbank vegetation is of high importance both for preserving the form (morphology) and function (ecology) of natural river systems. Revegetation of riverbanks is commonly used as a means of stream rehabilitation and management of bank instability and erosion. In this experimental study, the effect of different riverbank vegetation densities on flow hydrodynamics across the channel, including the riparian zone, are reported and discussed. The configuration of vegetation elements follows either linear or staggered arrangements as vegetation density is progressively increased, within a representative range of vegetation densities found in nature. Hydrodynamic measurements including mean streamwise velocity and turbulent intensity flow profiles are recorded via acoustic Doppler velocimetry (ADV)-both at the main channel and within the riverbank. These results show that for the main channel and the toe of riverbank, turbulence intensity for the low densities (λ ≈ 0 to 0.12 m −1 ) can increase up to 40% compared the case of high densities (λ = 0.94 to 1.9 m −1 ). Further analysis of these data allowed the estimation of bed-shear stresses, demonstrating 86% and 71% increase at the main channel and near the toe region, for increasing densities (λ = 0 to 1.9 m −1 ). Quantifying these hydrodynamic effects is important for assessing the contribution of physically representative ranges of riparian vegetation densities on hydrogeomorphologic feedback.

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“…According to the present regulations on the control of hillside land development in Taiwan, hillside land developmental projects have to be reviewed by the following four types of departments: land development planning, building design, soil and water conservation and environmental impact evaluation. A series of laboratory experiments were performed to investigate the connection between agricultural land and the key geomorphology around the vegetation [3].…”

Section: Literature Reviewmentioning

confidence: 99%

Enhanced Effects of Flood Disasters Due to Hillside Development in Urban Areas

Teng

Chen

2013

Water

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Abstract:In recent years, the Taiwan government has established a number of flood control facilities such as dikes, pumping stations and drainage systems to effectively reduce downstream flooding. However, with continued development and urbanization of catchment areas, the original designs of most flood control facilities have become outdated. Hillside lands in the upper and middle reaches of river basins have undergone urban development through unsound engineering practices, paving the way for heavy downstream flooding. Therefore, proper river basin management should include both upstream and downstream sides. The main purpose of the paper is to simulate non-urban inundation areas with various degrees of development (0%, 10%, 20%, 40% and 60%), over two different return periods of 25 years and 200 years, for intensive rainfall events in the Shi-Chi District, Taiwan. Through hydrological analysis and numerical simulations of inundation, quantitative data on inundation potential have been established based on the land development conditions along the hillsides on the upper and middle reaches of the Keelung River Basin. The simulated results show that the increase in the extent of land development in the upper reaches causes an increase in the area and depth of inundation, resulting in an increased risk of flooding in downstream areas. If the land-use policy makers in the upper reaches of the river basin's hillsides do not properly manage the land development, the risk of flooding in downstream areas will increase. In such an event, the policy makers should first review the situation to understand the problem with the consideration of this study. Thus, proper development and flood mitigation in hillsides can be established. OPEN ACCESSWater 2013, 5 225

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Observations on flow and local scour around submerged flexible vegetation

Cited by 44 publications

References 32 publications

Feedback between sediment and light for seagrass: Where is it important?

Feedback between sediment and light for seagrass: Where is it important?

Flow Hydrodynamics across Open Channel Flows with Riparian Zones: Implications for Riverbank Stability

Enhanced Effects of Flood Disasters Due to Hillside Development in Urban Areas

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