Fundamental Study on the Behaviour of Submarine Groundwater Discharged into the Coastal Sea

In order to investigate the behaviour of submarine groundwater flowing into the ocean, field observation, hydraulic tank experiments, and numerical simulations were carried out. As the results, the early-stage behaviour of the discharged submarine groundwater as density plume could be categorized into three types due to the ratio of discharge velocity to the background horizontal current velocity. When the ratio is relatively large, the behaviour of the discharged water can be predicted by the conventional theoretical model for the density plume. When the velocity ratio is relatively small, the inclination of the plume path gets smaller than the predicted values by the conventional model. It is because the effect of background diffusion becomes larger. If the velocity ratio is very small, the discharged water is transported almost along the sea bottom, which is the situation of the field observation. This result suggests that the submarine groundwater discharge in Toyama Bay supplies the nutrients for the benthic producer such as seagrass, rather than for the pelagic phytoplankton.