Hydrodynamic Response of a Floating Aquaculture Farm in a Low Inflow Estuary

Abstract

AbstractThe impact of a floating oyster aquaculture farm on the intratidal dynamics of a low inflow estuary was investigated using field observations and an idealized numerical model. Measurements of current velocities, temperature, electrical conductivity, and velocity shear were collected around a floating oyster farm during two semidiurnal tidal cycles in a curved portion of the estuary. During flood, farm‐induced friction enhanced the lateral straining of velocity shears, which induced vertical mixing near the surface and extended the farm's frictional footprint. The streamwise flow reduction near the farm limited the development of lateral circulation. During ebb, flows largely bypassed the farm, which resulted in a weaker streamwise flow reduction through the farm and allowed the lateral circulation to develop across the estuary. To capture the farm effects in numerical simulations, a bulk drag coefficient for the farm was calculated as 8.4 × 10−3 ± 9.1 × 10−4, while the drag for a single cage ranged from 0.58 to 0.92. An idealized simulation in the Regional Ocean Modeling System (ROMS) demonstrated that the limited development of lateral circulation during flood was due to farm‐imposed friction rather than the combined influence of channel‐shoal morphology and the natural channel bend. These results showed that even though a farm may encompass a small portion of the estuary, it can affect the momentum and mixing outside of the immediate farm area. Therefore, it is important to consider the hydrodynamic responses of farms in estimates of carrying capacity and siting decisions.