Abstract
Understanding the spatiotemporal variability of surface moisture on a beach is a necessity to develop a quantitatively accurate predictive model for aeolian sand transport from the beach into the foredune. Here, we analyze laser-derived surface moisture maps with a 1 × 1 m spatial and a 15-min temporal resolution and concurrent groundwater measurements collected during falling and rising tide at the barred Egmond beach, the Netherlands. Consistent with earlier studies, the maps show that the beach can be conceptualized into three surface moisture zones. First, the wet zone just above the low tide level: 18–25%; second, the intertidal zone: 5–25% with large fluctuations. In this zone, surface moisture can decrease with a rate varying between ∼2.5–4% per hour, and cumulatively with 16% during a single falling tide; and, third, the back beach zone: 3–7% (dry). The bar–trough system perturbs this overall zonation, with the moisture characteristics on the bar similar to the upper intertidal beach and the trough always remaining wet. Surface moisture fluctuations are strongly linked to the behavior of groundwater depth and can be described by a ’Van Genuchten-type’ retention curve without hysteresis effects. Applying the Van Genuchten relationship with measured groundwater data allows us to predict surface moisture maps. Results show that the predictions capture the overall surface moisture pattern reasonably well; however, alongshore variability in groundwater level should be improved to refine the predicted surface moisture maps, especially near the sandbar.
Highlights
Aeolian sand transport from the beach contributes to dune growth and recovery after erosion from storm-wave processes
There is a steep incline in moisture content around the high water line (x ∼ −5 m), as surface moisture in the intertidal zone varies from 10% surface moisture towards complete saturation of
With our Terrestrial Laser Scanner (TLS)-derived, high-resolution, spatiotemporal surface moisture maps, we have shown how surface moisture varies during falling and rising tide on a mildly sloping (∼1:30) beach consisting predominantly of quartz sand with a well sorted grain size distribution (D50 = 250–300 μm)
Summary
Aeolian sand transport from the beach contributes to dune growth and recovery after erosion from storm-wave processes. Well-developed dune-erosion models (e.g., van Gent et al [1], Roelvink et al [2]) are already in use for scientific and applied studies. Dune-growth models driven by aeolian-process dynamics are less advanced and are generally conceptual [3]. Recently introduced dune-growth models by Delgado-Fernandez [4], Keijsers et al [5], and Hoonhout and De Vries [6] show promising results. Prediction of aeolian sediment transport remains unsolved at a variety of temporal and spatial scales. Limiting factors of aeolian sand transport play an important role in solving and improving these predictions [10]
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