Tidal effects on submarine groundwater discharge into the ocean

Semi‐monthly, diurnal and semi‐diurnal variations of Submarine Groundwater Discharge (SGD) were found in Osaka bay, Japan, by continuous measurements of SGD using newly developed automated seepage meters. SGD increased sharply from neap to spring tide with semi‐monthly period. SGD also changes with diurnal and semi‐diurnal periods due to changes in hydraulic gradient between the groundwater and seawater in the coastal zone. SGD variations with semi‐monthly period by neap‐spring tidal pumping is much larger than those with diurnal and semi‐diurnal variations by tidal height changes.