Plume discharge strategies for artificial downwelling in stagnant linear stratified environments

Abstract

Artificial downwelling (AD) potentially mitigates oceanic hypoxia by utilizing pipelines or other artificial structures to transport oxygen-rich seawater from the surface to greater depths. However, limited research has focused on determining the discharge parameters for surface waters, which can often rise back to the upper layer or scour the seafloor sediments if discharged at inappropriate parameters. To address this issue, this study proposes a theory for determining the optimal discharge height of oxygen-rich plumes based on their hydrodynamic characteristics. Laboratory experiments were conducted in a linearly stratified flume to validate the theoretical model. The results show that the proposed theory can effectively calculate the important parameters of the AD jet, including the maximum depth, spread depth, and thickness of the intrusion layer. Furthermore, based on the theory of optimal discharge height, this paper provides plume discharge strategies for a typical AD device in field applications to regulate the operating parameters of the AD equipment, which can effectively keep the oxygen-enriched seawater completely in the hypoxic layer, avoid sediment-suspended secondary pollution, and maximize the oxygenation efficiency in different sea conditions.