Abstract
Cheniers are important for stabilising mud-dominated coastlines. A chenier is a body of wave-reworked, coarse-grained sediment consisting of sand and shells overlying a muddy substrate. In this paper we present and analyse a week of field observations of the dynamics of a single chenier along the coast of Demak, Indonesia. Despite relatively calm hydrodynamics during the one-week observational period, the chenier migrated surprisingly fast in the landward direction. The role of the tide and waves on the cross-shore chenier dynamics is explored using velocity moments as a proxy for the sediment transport. This approach shows that both tide and waves are capable of transporting the sediment of the chenier system. During calm conditions (representative for the south-east monsoon season), the tides generate a landward-directed sediment transport when the chenier crest is high relative to mean sea level. Waves only generate substantial sediment transport (direct, via skewness, and indirect, via stirring) when the chenier is submerged during periods with higher waves. The cross-shore chenier dynamics are very sensitive to the timing of tide and waves: most transport takes place when high water levels coincide with (relatively) high waves.
Highlights
A chenier is a beach ridge, resting on silty or clayey deposits, which becomes isolated from the shore by a band of tidal mudflats [1,2]
We focus on the last week of observations, a period during which the chenier became very dynamic
Mean Sea Level corresponds to z = 0, the origin of the x-axis is situated at the WaveDroid offshore (S0), and the coastline is around x = 5800
Summary
A chenier is a beach ridge, resting on silty or clayey deposits, which becomes isolated from the shore by a band of tidal mudflats [1,2]. Chenier plains are associated with prograding littoral environments [1] or deltas [2] with a sufficient supply of fine sediments of which the relative importance varies in time [1,2]; winnowing of the fine sediment deposits gives rise to the sandy barriers. Chenier plain shores are generally characterised by low to moderate wave conditions, tides may range from micro-tidal to macro-tidal and periods of wave dominance alternate with periods of high sediment supply [1]. Nardin and Fagherazzi [4] demonstrate that chenier plains may develop in areas with persistent high waves and without alternating periods as long as a specific balance between sediment availability and wave action exists. Less well investigated examples include the chenier plains in China [8] and West Africa [9,10]
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