Author(s): Daisaku Sato; Hiromune Yokoki; Masamitsu Arita
Keywords: Numerical simulation; Flow field; Tide; Pollutant advection; Funafuti atoll
Abstract: Water contamination due to insufficient effluent treatment of domestic wastewater is concerned in the enclosed lagoon of Funafuti atoll, Tuvalu. However, the fundamental characteristics of water flow field in the lagoon are not understood enough. This study conducted the numerical simulations of the lagoonal flow field and virtual particles advection in order to estimate the characteristics of water flow field and water contamination condition in the lagoon of Funafuti Atoll. Comparison of the calculated current velocity and water surface elevation and the observed data showed good agreement. The calculated lagoonal flow field showed that dominant currents were driven by wind and dominantly towards east to west On the shallow reef-flat the high speed orbital currents were generated by tide. However the orbital currents influenced the limited area near the open reef-flat. In the nearshore zone of the Fongafale Island the flow velocity was low through a year. Numerical simulation of virtual particles advection indicated that the particles, which were installed in the nearshore of Fongafare Island, were transported to the west side of the atoll through a year. In the non-trade-wind season, the high retention of installed particles was calculated in the lagoon. The simulated result provides important information for lagoonal environment conservation because the west side of the atoll is established as the preservation area by Tuvalu.