Abstract:Vertical structure of tidal current in a typically coastal raft culture area is discussed by a numerical model. A one dimensional hydrodynamic model was modified to include the tidal surface boundary layer for describing the interaction between aquaculture and tidal flow and parameterized with the field data. It replicated the observed velocity profile and was then used to investigate the impacts of varying culture densities and bottom frictions on the vertical tidal current structure. Modeling results indicate that the surface current velocity was largely damped because culture activities enhanced the frictional effects on flow intensively. The magnitude and vertical structure of tidal current are determined by aquaculture drag and bottom friction. The magnitude damps so rapidly that the vertical double log profile is distorted within a water column when the frictional effect of culture density increases to a certain threshold value. The vertical structure is remarkably deformed by the varying magnitude of bottom friction. In addition, the vertical velocity structure has a nonlinear trend along with culture density and bottom friction. The variation of the vertical structure is a kind of adaptation/adjustment to both surface friction (aquaculture drag) and bottom shear stress under the tidal forcing. This study is a theoretical foundation for optimizing aquaculture configuration through regulating culture density and species distribution. The frictional effect of culture organisms growth and suspended cage on the flow should be considered in further studies.
