Parameterized model for drag coefficient of raft culture in coastal waters and its application for hydrodynamic environment effect evaluation

Abstract

• Flow attenuation in coastal waters resulted from raft culture was evaluated by model. • A parameterized model was developed to simulate the flow drag of raft culture. • The model considered the effects of spacing and submerged length of culture units. • The mean velocity in the culture area decreased by 23.22% in Shenzhen Bay of China. Large scale raft culture, a common aquaculture in coastal areas, has an important impact on the hydrodynamic and ecological environments of coastal waters due to its water blocking effect. The flow resistance of raft culture was formulated by a parameterized model (PM) to describe the loss of flow momentum. Based on the classical theory of flow around cylinders using computational fluid dynamics (CFD), the proposed dimensionless PM took into account the effects of both spacing and submerged length of culture units. And the culture density was decomposed into two orthogonal directions along culture unit arrangement. The drag coefficient calculated by the PM agreed well with the CFD results. To verify the PM’s effectiveness, the Delft3D model with the PM was applied to Shenzhen Bay of China, waters with large-scale oyster raft culture. Compared with the observation, the numerical results with the PM agreed better than those without the PM. And the results showed that in Shenzhen Bay, the annual average velocity decreased by 23.22% in the culture area, while in the nearby channel outside the culture area, the annual average velocity increased by 15.65%. The model provides a useful tool for scientific management and evaluation for coastal aquaculture and coastal waters.