Evaporation on Seepage Face of Intertidal Zone Induced Groundwater Flow and Solute Transport in Subterranean Estuary

Tidal flat with very gentle slope distributes extensively around the world, e.g., the coastline of Bohai and Yellow Sea of China. Due to small slopes, the intertidal zone can be as wide as several kilometers, leading to large-scale seepage faces (saturated surface with groundwater efflux) during ebb and low tides. Evaporation on these seepage faces, with salt retained and accumulated, may significantly impact the density-dependent groundwater flow in subterranean esturay beneath the tidal flats. However, there is neither explicite boundary condition nor numerical model to quantify these processes due to nonlinear complexities of the groundwater flow and solute transport on seepage faces. Here we provide both mathematical and numerical models to quantify these processes. Numerical simulatuions show that seepage-face-evaporation can (1) significantly increase the salinity in the upper intertidal zone, thus promoting the generation and development of salt-fingering flows and affecting the spatial and temporal distributions of saline plume, (2) change the traditional groundwater flow field with freshwater discharge tube disappeared and upper saline plume incorporated into saltwater wedge, (3) reduce the scale of seepage faces, (4) promote the intertidal submarine groundwater discharge as well as the seawater-groundwater circulation.