Multiple Seepage‐Faces in Tidal Flat With Very Gentle Slopes

Abstract

<p>Large-scale seepage-faces occur on small-slope tidal flats. All previous studies assume that theseepage-face has only one single exit point. Here we show via numerical simulations of tidally-influencedgroundwater flow that, in a two-dimensional vertical, homogeneous transect of a tidal flat with gentle beachslope of 1‰, multiple seepage-faces may occur with at most four unsaturated beach surface segmentswhich separate four seepage-faces. Salinity-variation induced density-dependent flow leads to this complexphenomenon. While the seepage-faces are the groundwater discharging zones on the beach surface, theunsaturated zones are the recharging zones. The whole aquifer beneath the tidal flat is almost occupied byseawater and forms a wall blocking the horizontal seaward discharge of inland fresh groundwater so that inlandfreshwater discharges mainly occur near the high tide mark. This is in great contrast with the traditional resultsthat inland freshwater discharge occurs mainly near low tide mark.<br></p>