The influence of groundwater depth on coastal dune development at sand flats close to inlets

Filipe Galiforni Silva,Suzanne J M H Hulscher,Kathelijne M Wijnberg,Alma V De Groot

doi:10.1007/s10236-018-1162-8

Abstract

A cellular automata model is used to analyze the effects of groundwater levels and sediment supply on aeolian dune development occurring on sand flats close to inlets. The model considers, in a schematized and probabilistic way, aeolian transport processes, groundwater influence, vegetation development, and combined effects of waves and tides that can both erode and accrete the sand flat. Next to three idealized cases, a sand flat adjoining the barrier island of Texel, the Netherlands, was chosen as a case study. Elevation data from 18 annual LIDAR surveys was used to characterize sand flat and dune development. Additionally, a field survey was carried out to map the spatial variation in capillary fringe depth across the sand flat. Results show that for high groundwater situations, sediment supply became limited inducing formation of Coppice-like dunes, even though aeolian losses were regularly replenished by marine import during sand flat flooding. Long dune rows developed for high sediment supply scenarios which occurred for deep groundwater levels. Furthermore, a threshold depth appears to exist at which the groundwater level starts to affect dune development on the inlet sand flat. The threshold can vary spatially depending on external conditions such as topography. On sand flats close to inlets, groundwater is capable of introducing spatial variability in dune growth, which is consistent with dune development patterns found on the Texel sand flat.

Highlights

Inlet processes can define several types of barrier island terminus-shapes (Fitzgerald et al 1984; van Heteren et al 2006; Mulhern et al 2017)
Our findings suggest that groundwater level induces spatial variability in sediment supply and dune development in sand flat environments near inlets
A cellular automata model was used to understand the relation between groundwater level and aeolian dune development on sand flats close to inlets

Summary

Introduction

Inlet processes can define several types of barrier island terminus-shapes (Fitzgerald et al 1984; van Heteren et al 2006; Mulhern et al 2017). For barrier islands at the Dutch Wadden sea region, terminus-shapes are typically developed as wide sand flats. Those sand flats are large (scale of km) flat accumulations of sand built by inlet processes that. Surface moisture is known to affect aeolian sediment transport, which on natural beaches can be related to groundwater levels (Arens 1996; Yang and Davidson-Arnott 2005; Oblinger and Anthony 2008; Bauer et al 2009; Houser and Ellis 2013). In a study on the Dutch island of Ameland, Poortinga et al (2015) suggest that high groundwater levels can be supply limiting in an event scale (i.e., length of days), and limit the amount of sand available for aeolian transport. On sand flats where the slope is close to zero, amplitude fluctuations of the water table tend to be at a minimum, whereas lag between water table and tide tends to increase landward (Horn 2002; Zhou et al 2013)

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