Tracing submarine groundwater discharge flux in Tolo Harbor, Hong Kong (China)

Liu, Yi; Jiao, Jiu Jimmy; Cheng, Ho Kwan

Tracing submarine groundwater discharge flux in Tolo Harbor, Hong Kong (China) | Traçage des débits sous-marins d’eaux souterraines dans le port de Tolo, Hong Kong (Chine) Trazado del flujo de descarga de agua subterránea submarina en Tolo Harbor, Hong Kong (China) 追踪(中国)香港吐露港海底地下水排泄通量 Rastreando o fluxo de descarga de águas subterrâneas submarina em Tolo Harbor, Hong Kong (China)

2018

Liu, Yi | Jiao, Jiu Jimmy | Cheng, Ho Kwan

Submarine groundwater discharge (SGD) is an important pathway for groundwater and associated chemicals to discharge to the sea. Groundwater levels monitored along a transect perpendicular to the shoreline are used to calculate SGD flux from the nearshore aquifer to Tolo Harbor, Hong Kong (China). The calculated SGD flux—recharge/discharge measured with Darcy’s Law methods—agrees well with estimates based on geo-tracer techniques and seepage meter in Tolo Harbor during previous studies. The estimated freshwater SGD is 1.69–2.0 m²/d at the study site and 0.3 ± 0.04 cm/d for the whole of Tolo Harbor, which is comparable to the river discharge (0.25 ± 0.07 cm/d) and precipitation (0.45 ± 0.15 cm/d). The tide-driven SGD in the intertidal zone is 13.98–17.59 m²/d at the study site and 2.42 ± 0.56 cm/d for the whole of Tolo Harbor. The SGD occurring in the subtidal zone and the bottom of Tolo Harbor is 3.12 ± 4.63 cm/d. Fresh SGD accounts for ~5% of the total SGD, while the rest (~95%) is contributed by saline SGD driven by various forces. About 96% of the tide-driven SGD in the intertidal zone occurs in the ebbing tide period because the head difference between the groundwater level and sea level is great during this period. Tide-driven SGD in the spring tide is ~1.2 times that during neap tide. The tidal fluctuation amplitude and tide-driven SGD in the intertidal zone are positively correlated to each other; thus, a spring neap variation of the tide-driven SGD is observed.

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