Estimation of seawater–groundwater exchange rate: case study in a tidal flat with a large-scale seepage face (Laizhou Bay, China)

Ma, Qian; Li, Hailong; Wang, Jerry H. C.; Wang, Chaoyue; Wan, Li; Wang, Xusheng; Jiang, Xiaowei

Estimation of seawater–groundwater exchange rate: case study in a tidal flat with a large-scale seepage face (Laizhou Bay, China) | Estimation de la vitesse d’échange entre eau de mer et eaux souterraines: cas d’étude d’un estran présentant une large surface d’échange (Baie de Laizhou, Chine) Estimación de la tasa de intercambio agua subterránea–agua de mar: un caso de estudio en la planicie mareal con una fase de filtración a gran escala (Laizhou Bay, China) 海水-地下水交换率估测: (中国莱州湾) 一个具有大规模渗透面的潮汐滩地研究实例 Estimação das taxas de permuta água subterrânea-água superficial: estudo de caso numa planície de maré com uma interface de percolação de larga escala (Baía de Laizhou, China)

2015

The exchange rate between seawater and groundwater in a tidal flat was investigated at Laizhou Bay, China, where there are large-scale seepage faces with horizontal extension of several hundred meters developed during low tides. Taking into account the effects of seepage face and density, a simple and efficient method for estimating seawater–groundwater exchange rate is proposed, based on field measurements of groundwater hydraulic head, temperature and salinity. First, the exchange rate at each well was obtained using the generalized Darcy’s law, then the results were interpolated and integrated along the whole transect. The total submarine groundwater discharge (SGD) and inflow were estimated to be 8.8 and 15.3 m³d⁻¹ m⁻¹, respectively. The spatial distributions of SGD and inflow were different from those of sandy or gravel beaches possibly owing to the low-permeability sediment (silty sand with mud), very gentle slope, and the large-scale seepage faces. A freshwater discharge tube was identified near the low-tide line, as evidenced by significant increase in outflow and low salinity of groundwater observed there. The SGD from the seepage faces accounted for ∼21 % of the total SGD. The outflow rate that occurred from the seepage faces, and the ratio of the outflow from the seepage faces to the total outflow, decreased seaward significantly and monotonically.

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