Following the success of the DYNAREV experiment in the summer of 2017, a second Bath-led laboratory experiment on a low cost style of dynamic revetment was carried out in collaboration with researchers from institutions in both Europe and Brazil, supported by GCRF funding.
Traditionally, coastal protection uses solutions such as sea walls or beach nourishment. However, recent research has been conducted on a new type of defence termed ‘Dynamic Revetments’, these revetments are designed to mimic composite beaches commonly found on the British coast and other places around the world. Consisting of cobble berm placed above the normal wave run-up limit, the structure has a dynamic morphology meaning it adapts to the current wave conditions by changing shape. This provides stability to the upper beach and overtopping protection.
Both experiments were carried out in the 300m Groẞer Wellenkanal (GWK) flume based in Hannover. The previous experiment was carried out using high quality material with a low degree of cobble variation in both size and angularity. In contrast, the more recent experiment uses poorly sorted cobbles with a high degree of variability in both size and shape. The main idea being that such material is both cheaper and easier to attain for construction purposes, notably this could be taken from quarry run-off meaning greater access globally to the use of dynamic revetments. The specific research aims for the second experiment are on-going and set out as follows;
I. Determine the performance of a dynamic revetment using varied cobbles under a both energetic wave conditions and incremental sea level rise. This also includes foreshore response to the conditions with and without the revetment. Further, compare and contrast the findings from the revetment constructed in DYNAREV with that constructed in DYNAREV-2, comparing morphology and retreat of the revetment.
II. Test the recovery process of the dynamic revetment by testing its ability to reform after energetic wave conditions. Test maintenance of the structure by cobble ‘re-nourishment’. This involves dumping large quantity of cobbles to replace cobbles that have been lost due to various processes.
III. Using both experiments to improve theoretical understanding of the physical processes in dynamic revetments and improve the current modelling ability for such structures. These may ultimately lead to both model based design tools and preliminary guidance for construction, something which is currently lacking for groups interested in testing such concepts.
The near prototype scale revetment constructed at GWK was monitored using a vast array of instruments including Lidar, high resolution cameras and mechanical profilers. Measurement were taken for stability, morphology and performance of the revetment as well as cobble transport. Additionally, morphology of the beach was monitored, focussing on bar formation and indicators of sand erosion from beneath the revetment.
This was followed by a re-nourishment regime for the revetment. This involves placing a large quantity of fresh material on the face of the structure and monitoring the resulting morphology change under wave attack. This is vital for the long term viability of such structures and is an important consideration for their applicability in many locations.
As the current impacts on the climate worsen it is expected that storms will increase in both severity and occurrence. Combined with increasing sea levels this translates to significantly increased risk for coastal regions. Therefore new and effective coastal protection is required to supplement coastal defence regimes, many of which risk becoming obsolete in the future.
Traditional methods are often expensive and aesthetic focussed, however this approach is not appropriate for many regions. This project offers an alternative for regions where either lower cost solutions are required or areas which cannot afford coastal retreat but are largely undeveloped. This potentially makes the dynamic revetment both versatile and important to future coastal protection schemes.
This has important consequences for developing countries, due to the low cost and relatively easy construction as demonstrated by the current dynamic revetment at North Cove, Washington. It is expected that they will form part of any such coastal protection schemes.