A Semi-empirical Method to Assess Flow-Slide Probability

Ham, G.A. Van den; Groot, M.B. de; Mastbergen, Dick R.

doi:10.1007/978-3-319-00972-8_19

Cited by 9 publications

(37 citation statements)

References 9 publications

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“…In the Netherlands, flow slide risk research today is part of flood risk assessment required by law. Flow slides are presently assumed to be either breaching or liquefaction failures [31]. However, post-event bathymetry measurements do not reveal conclusive information on the geo-mechanical failure mechanism involved.…”

Section: Liquefaction or Breaching?mentioning

confidence: 99%

“…The sand needs to be sufficiently fine grained (about 100-200 µm), freshly deposited (in general young uncemented Holocene marine sands), and not containing too much clay which could make the sediments more cohesive and less prone to breaching. More advanced methods to assess flow slide occurrence and flood risk have been developed in the Netherlands [21,31].…”

Section: Anatomy Of An Rbf Eventmentioning

confidence: 99%

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Watching the Beach Steadily Disappearing: The Evolution of Understanding of Retrogressive Breach Failures

Mastbergen

Beinssen

Nédélec

2019

JMSE

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Retrogressive breach failures or coastal flow slides occur naturally in the shoreface in fine sands near dynamic tidal channels or rivers. They sometimes retrogress into beaches, shoal margins and riverbanks where they can threaten infrastructure and cause severe coastal erosion and flood risk. Ever since the first reports were published in the Netherlands over a century ago, attempts have been made to understand the geo-mechanical mechanism of flow slides. In this paper we have established that events, observed during the active phase, are characterized by a slow but steady retrogression into the shoreline, often continuing for many hours. This can be explained by the breaching mechanism, as will be clarified in this paper. Recently, further evidence has become available in the form of video footage of active events in Australia and elsewhere, often publicly posted on the internet. All these observations justify the new term 'retrogressive breach failure' (RBF event). The mechanism has been confirmed in flume tests and in a field experiment. With a better understanding of the geo-mechanical mechanism, current protection methods can be better understood, and new defense strategies can be envisaged. In writing this paper, we hope that the coastal science and engineering communities will better recognize and understand these intriguing natural events.

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Section: Liquefaction or Breaching?mentioning

confidence: 99%

Section: Anatomy Of An Rbf Eventmentioning

confidence: 99%

Watching the Beach Steadily Disappearing: The Evolution of Understanding of Retrogressive Breach Failures

Mastbergen

Beinssen

Nédélec

2019

JMSE

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“…‘Collapses’ refer to a downfall of the elevation in the morphology in a relatively short time. The style and development of failure processes are controlled by flow conditions, slope geometry and sand properties (Stoutjesdijk et al , ; Olson and Stark, ; Deangeli, ; Van den Ham et al , ). The morphological and societal importance of shoal margin collapses is considerable: typically, events occur up to several million cubic meters in the Western Scheldt (Figure ) and approach annually dredged volumes of 10 × 10 6 m 3 (Wang and Winterwerp, ; Dam et al , ; Jeuken and Wang, ).…”

Section: Introductionmentioning

confidence: 99%

“…Two fundamentally different types of underwater shoal margin collapses occur: rapid flow slides due to liquefaction and the more dominantly slow retrogressive flow slides due to breaching (Van den Berg et al , ; Van den Ham et al , ; Mastbergen et al , ). Flow slides occur at lower angles and displace much more sediment over much larger distances than the well‐known classic (river) bank shear failure that is followed by a slump or slide over a short distance (Simon and Collinson, ; Kleinhans et al , ).…”

Section: Introductionmentioning

confidence: 99%

“…The general failure mechanisms of channel banks proceed from undercutting by sand removal on the transverse bed slope at the bank toe. The processes of liquefaction and breaching require different conditions (see Van den Berg et al , ; Van den Ham et al , ). Liquefaction requires loosely packed, non‐lithified and water‐saturated sand or silt (Lowe, ), whereas breaching requires the presence of a sufficiently large body of densely packed fine sand or silt (You et al , ; Van den Berg et al , ).…”

Section: Introductionmentioning

confidence: 99%

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Location and probability of shoal margin collapses in a sandy estuary

Dijk

Mastbergen

Ham

et al. 2018

Earth Surf Processes Landf

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Channel bank failure, and collapses of shoal margins and beaches due to flow slides, have been recorded in Dutch estuaries for the past 200 years but have hardly been recognized elsewhere. Current predictions lack forecasting capabilities, because they were validated and calibrated for historic data of cross-sections in specific systems, allowing local hindcast rather than location and probability forecasting. The objectives of this study were to investigate where on shoal margins collapses typically occur and what shoal margin collapse geometries and volumes are, such that we can predict their occurrence. We identified shoal margin collapses, generally completely submerged, from bathymetry data by analyzing digital elevation models of difference of the Western Scheldt for the period 1959-2015. We used the bathymetry data to determine the conditions for occurrence, specifically to obtain slope height and angle, and applied these variables in a shoal margin collapse predictor. We found 299 collapses along 300 km of shoal margin boundaries over 56 years, meaning that more than five collapses occur on average per year. The average shoal margin collapse body is well approximated by a 1/3 ellipsoid shape, covers on average an area of 34 000 m 2 and has an average volume of 100 000 m 3 . Shoal margin collapses occur mainly at locations where shoals take up a proportionally larger area than average in the cross-section of the entire estuary, and occur most frequently where lateral shoal margin displacement is low. A receiver operating characteristic curve shows that the forecasting method predicts the shoal margin collapse location well. We conclude that the locations of the shoal margin collapses are well predicted by the variation in conditions of the relative slope height and angle within the Western Scheldt, and likely locations are at laterally relatively stable shoal margins. This provides hypotheses aiding the recognition of these features in sandy estuaries worldwide.

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