University of Bath

Dynamic Coastal Protection: Resilience of Dynamic Revetments Under SLR (DynaRev)

This study will investigate the response of a sandy beach to sea level rise and the ability of a cobble revetment to enhance resilience and coastal recession.

Waves impacting the revetment tested in the large scale flume
Waves impacting the revetment tested in the large scale flume

While hard engineering protection may well be required in highly developed areas where the economic and social implications of failure are disastrous, in some areas a lower level of protection may be acceptable. A relatively recent shore protection method is the use of what have been variously termed “dynamic revetments”, “cobble berms” or “rubble beaches”. This approach involves the construction of a gravel or shingle ridge around the wave runup limit to mimic composite beaches which consist of a lower foreshore of sand and a backshore ridge constructed of gravel or cobbles which stabilises the upper beach and provides overtopping protection to the hinterland. These structures contrast with static coastal defence structures as they are “dynamic” and are expected to reshape under wave attack. Experience has shown that these structures perform well in terms of limiting wave runup and overtopping, though little information is available regarding their effect on the natural sand beach profile and their performance in a SLR scenario is unknown.

The berm crest of a gravel beach is generally formed just below the maximum level of wave runup (Bradbury and Powell, 1992) and studies have suggested that during severe storms material can be pushed up to or beyond the crest by extreme runup events causing the berm to gain elevation and roll landwards (Carter and Orford, 1984). The hypothesis of the proposed study is that the dynamic nature of dynamic revetments means that with sufficient maintenance of material volume they can evolve to maintain their elevation relative to the rising sea level and provide a relatively low impact, adaptive and innovative solution to coastal protection.

In addition to their potential adaptive nature in response to SLR, in some locations dynamic revetments may be seen as a more sustainable approach to coastal protection for a number of reasons including:

  • They allow the beach to maintain a level of ‘natural’ character.
  • Stone size is smaller and typically less expensive than for static (large rock) protection structures.
  • Construction can be achieved by randomly placing material as there is no requirement for multiple carefully designed armour layers or individual placement of armour stones.
  • Such coastal protection structures are easy to maintain and reshape if they move out of their allowable dynamic range.

This project is led by the University of Bath with partners from the UK, Europe and further afield. The team will construct a prototype-scale beach in the world’s largest coastal engineering wave flume (GWK, Hannover) during summer 2017 and investigate the response of the beach to a rising sea level with and without a dynamic revetment structure through 3 main work packages (WP):

WP1 - Performance of Dynamic Revetments Determine the performance of dynamic revetments to a rising sea-level and their resilience in response to a range of high and low-energy wave conditions. Analyse the response of the sandy foreshore to SLR with and without the presence of a revetment.

WP2 – Fundamental Hydrodynamic and Sediment Transport Processes Gain fundamental information about wave transformation in the surf and swash zones, beachface morphology change and the dynamics of nearshore bars due to changing waves and water levels. This fundamental knowledge will enable an understanding of the revetment performance and beach response to SLR, potentially indicating approaches to improve revetment design and beach resilience.

WP3 – Numerical modelling Test and improve the capabilities of parametric and process-based models in predicting wave transformation and morphology changes of the sandy beach alone and in presence of the dynamic revetment using the laboratory results. Generalize the results to prototype conditions to optimise the dynamic coastal protection design in the presence of SLR.