Artificial rock reefs bring new life to Hollandse Kust Zuid
Objectives
To investigate whether the deployment of rock reefs, using a rock grading larger than that used for conventional scour protection, offers additional benefits for Atlantic cod and other reef-associated species (fishes, invertebrates).
Short description
The deployment of rock reefs took place in 2021-2022 as part of the Nature Inclusive Building Plan at four locations within the Hollandse Kust ZuidHollandse Kust Zuid is located 18 to 34 km off the Dutch coast. It comprises of 140 turbines and a total combined installed capacity of 1,500 MW. Offshore Wind Farm. Following consultations with Dutch authorities, five additional reefs were deployed, bringing the total number of reef locations to nine. These reefs are constructed using large rocks (700-1000 kg grading, with a D50 of approximately 80 cm) placed on top of the regular scour protection layer. Each reef has a diameter of approximately 8 meters and a height between 1.5 and 2 meters. They are positioned at least 10 meters away from the foundation and at least 10 meters away from the cables at the bottom of the scour protection layer. The aims of the rock reef deployment and monitoring campaigns are: 1) to gather empirical evidence on how rock reefs contribute to the abundance of Atlantic cod and overall biodiversity; 2) to investigate technical aspects, costs and risks associated with monitoring; and 3) to estimate the feasibility of applying rocks reefs as Nature Inclusive Design (NID) elements on an offshore wind farm at scale.
The ecological monitoring of the rock reefs is integrated into various monitoring campaigns. The KOBINE project, led by Wageningen Marine Research, aims to quantify the biodiversity gains (e.g., metrics on species richness) in relation to the construction and maintenance costs of these rock reefs. The project will provide insights into the types of ecological benefits that can be achieved through various cost-effective measures and will develop a cost-benefit modeling tool. Additionally, the rock reefs are being monitored by Waardenburg Ecology as part of the NID monitoring plan at HKZ. They employ various techniques, such as baited cameras and eDNA sampling, to gain insights into the potential functions (e.g,. shelter, feeding) provided by the new habitats and assess the potential biodiversity effects in comparison to conventional scour protection.