Sustainability report 2019

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a global NGO. The sandstone units were 3D printed in Rotterdam by Boskalis using D-shape technology. 50 units were printed, ranging in height from 50 to 120 cm. In May 2018, 80,000 oysters on the artificial reefs and in four research cages. By the end of 2019, observations of the reefs identified evidence of a new generation of oysters growing on the installation, indicating that the oyster population will be able to grow organically. This has the potential to revive the flat oyster in the North Sea. The population had been largely destroyed in the North Sea due to over-fishing, disease and cold winters. Oyster banks have been shown to increase biodiversity by 60% as they provide a hard surface that encourages the growth of soft corals, wading fish, lobsters and North Sea crabs. They can also serve as a nursery for baby sharks and rays. HOUTRIB DIKE, NETHERLANDS The 27 kilometer long Houtrib Dike runs between the cities of Enkhuizen and Lelystad in the Netherlands. The Houtrib Dike serves as a breakwater between the IJsselmeer and the Markermeer during storms. This makes the Houtrib Dike vitally important for flood risk management in all provinces in the IJsselmeer region. In 2014, EcoShape together with Rijkswaterstaat (the Directorate- General for Public Works and Water Management) initiated a pilot to test a 450-metre-long sandy foreshore, which consisted of a body of sand of approximately 70,000 m³ as a method for strengthening the dike. The sandy foreshore reduces the wave action against the dike providing an effective protection for the dike. Sandy banks had not been used in a freshwater lake for flood risk management before. Although much was known about coastal sand reinforcements, the situation in the dike was different because the water level is constant and wave movements are less predictable, partly because of the influence of the wind. It was monitored for 4 years to understand the impact of waves on the foreshore and the effect of the growth of vegetation on the stability of the foreshore. Based on its success, Rijkswaterstaat incorporated the Building with Nature principles from the pilot project into the design of the full scale reinforcement of the Houtrib Dike. This meant scaling up of the pilot that used around 70,000 m 3 sand to a commercial project using around 10 million m 3 of sand. the Joint Venture partners responsible for the design and construction. In addition to the dike reinforcement, the nature reserve ‘Trintelzand’ was constructed through the beneficial reuse of dredged material, creating shallow areas and reed banks to attract fish and birdlife. In addition to flood protection and nature creation, the reserve also contributes to improving the water quality in the Markermeer. The adoption of the Building with Nature principles to create commercially viable projects that account for and benefit natural systems is an excellent example of what Boskalis is trying to achieve through its contribution to and collaboration with the EcoShape Partners. The execution of the Project Reinforcement Houtrib Dike started in 2018 and was finished in November 2019. Boskalis was one of

The approach integrates infrastructure design with the restoration of ecosystems that add value through coastal protection and flood regulation, as well as boosting local agricultural and fishery industries, recreation and biodiversity. Building with Nature’s sustainable solutions can be cheaper to construct and maintain while enabling more productive and multi-functional land-use. In 2019, a number of EcoShape and Building with Nature projects were executed. In the northern Wadden Sea in the Netherlands, the Koehoal Salt Marsh development with a Mud Motor investigated the potential for enhancing the development of a salt marsh. It did this by strategic placement of dredged maintenance sediments from the Port of Harlingen along the shores by making use of the transport capacity of the ambient flow. A second example is the Hondsbossche dunes. The project studies the development of nature on a large scale beach nourishment, including soft shallow foreshores and various dune habitats. Lessons learned are published through the Building with Nature design guidelines. OYSTER REEF RESTORATION, NORTH SEA In 2017 Reef Design Lab designed a series of 3D printed reef units for an oyster reef restoration research project in the North Sea for

SUSTAINABILITY REPORT 2019 – BOSKALIS