March 6, 2017

Design of Coastal Protection Works

The design and implementation of suitable technical measures to protect beaches from erosion are of high priority in order to achieve effective coastal zone adaptation to long- and short-term SLR. The particular characteristics of the Greek island beaches (small pocket beaches with low/intermittent/decreasing inland sediment input), as well as the special socio-economic circumstances and conditions, limit adaptation schemes, especially as particular management strategies (e.g. “Managed Retreat”) are not a viable option for the majority of cases. For that reason, adaptation choices are limited to either “soft” (beach nourishment/replenishment) or “hard” (construction of groynes, offshore breakwaters or seawalls) technical solutions.

“Ηard” Technical Responses

Hard technical measures for coastal protection involve massive structures made of concrete or accumulations of large rock blocks offering a range of design choices, such as (shore perpendicular) groynes with crests above mean sea level, systems of offshore submerged and/or low crested breakwaters.

In order to design the structure layout for the pilot beaches and test it under different scenarios of SLR, advanced mathematical simulations were carried out including numerical models such as: (1) WAVE-L for wave propagation, (2) WICIR for wave induced circulation and sea level rise and (3) SEDTR for sediment transport/long-term evolution of seabed morphology (ref). The simulations ran under different environmental conditions and design parameters (e.g. base depth/crest height length, width and distance from the shore), taking to account safety factors (e.g. dangerous littoral current formation) as well as possible environmental and aesthetic impacts of the structures. The final design choice was made based on evaluation of structure performance with respect to present demands as well as considering robustness and upgradability at low cost in the future.


“Soft” Technical Responses

In the past, responses to beach erosion involved mostly ‘hard’ technical measures. However, as the experience from the implementation of such measures has not been always satisfactory there is now an emerging trend for more environmentally friendly approaches arising from the need for more rational and functional adaptation options. The main focus of these measures is the mitigation of negative environmental impacts, such as the erosion of neighboring beaches, the quality of the nearshore waters and the aesthetics of the beach environment. Soft protection measures that are environmentally acceptable do not inhibit nearshore circulation and do not have (significant) impacts on the coastal ecosystems. In addition, if the priority is to maintain the beach under increasing sea levels, as it should be in the case of the touristic beaches of the Aegean islands, then the best available practice involves beach nourishment (artificial beach replenishment).

Beach nourishment is the modern response approach to coastal erosion, which is particularly applicable where beaches are by themselves a significant economic resource. The beach is replenished using sediments from other coastal areas with excess material and/or marine aggregates from deeper waters. The height at which the sediment is deposited on the beach is at 1-3 m above sea level. After initial deposition, wave-induced currents rearrange the newly deposited sediments and an equilibrium beach profile is established by the cross-shore sediment transport.

Beach nourishment technical characteristics were estimated by adapting the approach of  “Equilibrium beach profiles” proposed by Dean, 1990,  and thus,  the volume replenishment material under specific scenarios of sediment diameter (d50) ,  the extension of the beach width and berm height after replenishment were estimated for the pilot beaches.

ERA Beach Partners - Funding