Measurements of submarine groundwater discharge rates by a continuous heat-type automated seepage meter in Osaka Bay, Japan

Abstract

In order to evaluate submarine groundwater discharge (SGD) rates continuously and automatically, a "continuous heat-type" automated seepage meter was newly developed, and it was applied to Tannowa, Osaka Bay, Japan. The meter is based on the measurements of the temperature gradient of the water between the downstream and upstream positions in a pipe. According to two months continuous measurements of SGD every 10 minutes, semi-diurnal periodical changes in SGD were found in Tannowa. This is attributed to the tidal effects on SGD. The time delay of the SGD from tidal records was also found to be about 5 hours. The newly developed automated seepage meter can provide longer-term and higher-resolution measurements of SGD, which helps us to understand temporal scale issues on SGD and the relevant hydrological and coastal oceanographic processes.