ALBERT

Description: Beach nourishments are a widely used method to mitigate erosion along sandy shorelines. In contrast to hard coastal protection structures, nourishments are considered as soft engineering, although little is known about the cumulative, long-term environmental effects of both marine sediment extraction and nourishment activities. Recent endeavours to sustain the marine ecosystem and research results on the environmental impact of sediment extraction and nourishment activities are driving the need for a comprehensive up-to-date review of beach nourishment practice, and to evaluate the physical and ecological sustainability of these activities. While existing reviews of nourishment practice have focused on the general design (motivation, techniques and methods, international overview of sites and volumes) as well as legal and financial aspects, this study reviews and compares not only nourishment practice but also the accompanying assessment and monitoring of environmental impacts in a number of developed countries around the world. For the study, we reviewed 205 openly-accessible coastal management strategies, legal texts, guidelines, EIA documents, websites, project reports, press releases and research publications about beach nourishments in several developed countries around the world (Germany, Denmark, the Netherlands, Belgium, Spain, UK, USA and Australia). Where information was not openly available, the responsible authorities were contacted directly. The study elaborates on the differences in coastal management strategies and legislation as well as the large dissimilarities in the EIA procedure (where applicable) for both marine sediment extraction and nourishment activities. The spatial disturbance of the marine environment that is considered a significant impact, a factor which determines the need for an Environmental Impact Assessment, varies substantially between the countries covered in this study. Combined with the large uncertainties of the long-term ecological and geomorphological impacts, these results underline the need to reconsider the sustainability of nourishments as “soft” coastal protection measures.

Description: Aquaculture is projected to be a major supplier of marine proteins to large parts of the global population. This includes bivalves, which have a high potential to offset protein deficits, as they are highly adaptable to varying water temperature, salinity, desiccation, and oxygen conditions. This work is part of a two-piece contribution on novel marine aquaculture technology and details physical laboratory tests of a new cultivation system for bivalve farming called “Shellfish Tower”. The tested 1:20 model consists of a rectangular cage (2 × 2 m prototype scale) with a central buoyancy element and a height of 2 – 4 m. Testing was done in a current flume as well as a wave basin for current velocities between 0.4 – 2.2 m/s and wave heights of 1.6 to 5.0 m with periods between 5 to 14 s. The tests were conducted to prove the feasibility and functionality of this aquaculture system, which is usable for the collection and cultivation of mussel spat as well as for the grow-out of oysters, scallops, and seaweed in marine environments. Tests carried out in a current flume revealed that drag coefficients decrease with increasing current velocities, and range from Cd=0.5 to 2.5, while the mooring inclination increases from 12° to 84° with increasing flow velocity, which is highly dependant on the buoyancy related pretension. The examination of the mooring line tensions recorded in a wave basin showed that the largest values of snap-induced tension were up to 10 times that of the semi-static tension. The maximum-recorded tension on the system was 48 kN for a single and 89 kN for a double configuration, compared to non-snap tension values, which were in the range of 6 – 10 kN. The insights gathered in this study will inform the future design of aquaculture systems in high-energy environments and allow for an integration into numerical models.

Description: The purpose of this publication is to perform a system analysis of new cultivation technology for exposed bivalve farming. The technical feasibility of the new construction, called Shellfish Tower, was assessed. The device has gone through several very different phases of development on its way to the deployment of the prototype. These included multiple iterations during the designing stage, wave tank testing, fabrication, loading and unloading on trucks and vessels, deployment at sea, installation and assembly on the single mooring line, and bring it to its final position in a submerged mode 5m-10 m below the water surface. The final structure has a hexagonal body, with a centrally orientated variable buoyancy unit with culture sub-units on each of the six corners. These sub-units can be used for the culture of oysters (Magallana gigas – formally Crassostrea gigas) as well as for the collection of mussel spat (Perna canaliculus). Other possible candidates could be seaweed, lobsters, sponges or tunicates. The operational depth of the whole system can be at any depth but was tested at between 5 and 10 m below the water surface positioned on the mooring line between the screw anchor and surface floats for the prototype tests. The system was deployed in March 2019 six nautical miles off the Bay of Plenty, North Island (New Zealand), in exposed waters near a commercial mussel farm and has been in test mode since then. The modelled structure indicates a design tolerance of significant wave height of over 7 m and currents of over 0.8 m/s. Initial results show that the new design has survived waves at 4.6 m significant height and current velocities of up to 0.7 m•s-1, while showing best growth conditions of the cultured oysters as well as for the spat settlement of juvenile greenshell™ mussels.