Multiple Seepage‐Faces in Tidal Flat With Very Gentle Slopes

Abstract

AbstractLarge‐scale seepage‐faces occur on small‐slope tidal flats. All previous studies assume that the seepage‐face has only one single exit point. Here we show via numerical simulations of tidally‐influenced groundwater flow that, in a two‐dimensional vertical, homogeneous transect of a tidal flat with gentle beach slope of 1‰, multiple seepage‐faces may occur with at most four unsaturated beach surface segments which separate four seepage‐faces. Salinity‐variation induced density‐dependent flow leads to this complex phenomenon. While the seepage‐faces are the groundwater discharging zones on the beach surface, the unsaturated zones are the recharging zones. The whole aquifer beneath the tidal flat is almost occupied by seawater and forms a wall blocking the horizontal seaward discharge of inland fresh groundwater so that inland freshwater discharges mainly occur near the high tide mark. This is in great contrast with the traditional results that inland freshwater discharge occurs mainly near low tide mark.