Evaluation of submarine groundwater discharge in coastal aquifers at Osaka Bay, Japan by numerical simulation
Abstract
In recent years, the coastal marine ecosystems have been deteriorated by the human activities and fisheries. One of the causes of this deteriorating situation is due to the increase of nutrient fluxes caused by the fertilizers and wastewater through the surface water and groundwater discharges from the residential and agricultural areas into coastal areas. In recent studies, it is recognized that the groundwater which contains nutrients can have a significant influence on coastal ecosystems. Submarine groundwater discharge (SGD) consists of terrestrial fresh groundwater and recirculated seawater which circulate across the aquifer-ocean interface. Recirculating seawater, which often constitutes a large portion of the total SGD, is an important component as it transports not only salt but also other chemicals from the ocean to the aquifer. Near the shore, seawater recirculation across the interface is driven primarily by tidal oscillations, waves and density variations between fresh groundwater and seawater. Recent numerical simulations show the formation of water circulations in the aquifers near the shoreline owing to the tidal oscillations. However, these calculation results do not compare with a field observation and are not necessarily an enough verification. The objective of this study is to evaluate the SGD mechanism in the Omaehama, Osaka bay under the influence of tidal effects. The developed numerical model was verified by comparing the results with the observed SGD in the Osaka bay. The study area is located in the coast of Omaehama, Osaka, Bay, Nishinomiya citiy, Japan. The automated seeepage meters with diameter of 500mm and piezometer with diameter of 13mm were installed to evaluate water dynamics below the beach slop. Electric conductivity of the pore water were also observed to evaluate the terrestrial groundwater among SGD duaring one tidal cycle. The numerical model is based on the groundwater flow equation for saturated-unsaturated fluid flow and advection-dispersion equation for solute transport. This model have been developed to simulate groundwater flow and salt transport in an unconfined coastal aquifer subject to taidal forcing across a sloping beach boundary and inland fresh groundwater discharge. Numerical simulations with two differece changes of tidal fuluctuations have been done to evaluate the characteristic of the SGD. The results shows that seawater recirculation induced by tide was ocureed when the tidal fuluctuations was large. This result qualitatively agree with the observation results, therfore the numerical model incorporating tidal effects is uesful for evaluation of SGD including recirculated seawater.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.H21D0848Y
- Keywords:
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- 1828 Groundwater hydraulics;
- 1829 Groundwater hydrology;
- 1831 Groundwater quality;
- 1832 Groundwater transport