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Yvonne Smit
Utrecht University, Faculty of Geosciences

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Journal article
Published: 15 January 2019 in Hydrology
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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.

ACS Style

Yvonne Smit; Jasper J. A. Donker; Gerben Ruessink. Spatiotemporal Surface Moisture Variations on a Barred Beach and their Relationship with Groundwater Fluctuations. Hydrology 2019, 6, 8 .

AMA Style

Yvonne Smit, Jasper J. A. Donker, Gerben Ruessink. Spatiotemporal Surface Moisture Variations on a Barred Beach and their Relationship with Groundwater Fluctuations. Hydrology. 2019; 6 (1):8.

Chicago/Turabian Style

Yvonne Smit; Jasper J. A. Donker; Gerben Ruessink. 2019. "Spatiotemporal Surface Moisture Variations on a Barred Beach and their Relationship with Groundwater Fluctuations." Hydrology 6, no. 1: 8.

Preprint content
Published: 31 December 2018
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Foredune growth results predominantly from sand that is blown from the beach and backshore. Predictions of multi-year potential sand supply that are based on time series of wind speed and direction measured at a regional (offshore or coastal) meteorological station, however, often grossly overpredict measured deposition volumes on the foredune. This is commonly ascribed to supply limiting factors, such as beach surface moisture or shell deposits, or to fetch limitations. Here we show that differences between regional and local (i.e., on the beach) wind characteristics can also contribute substantially to this overprediction. Using wind data collected during a five-week field experiment on a Dutch beach backed by a 20-m high, steep (1:2) foredune we found that the wind speed on the beach is lower and that the wind direction on the backshore is more alongshore than expected from the regional wind data. Both the difference in speed and direction were a function of the regional wind direction, with the largest speed reduction (to about 70% of the regional value) for shore-normal winds and the largest alongshore deflection (about 15 degrees) for shore-oblique winds. When these functional dependencies are applied to a 10-year series of regional wind data, we found that the potential annual onshore sand transport at our site, predicted with the aeolian sand transport equation of Hsu (1971), reduces from 86 to 24 m3/m. The latter is now comparable, although still somewhat higher than the measured annual deposition volume of 10 to 15 m3/m. Further analysis of the computations shows that most of this reduction is due to the difference between regional and local wind speed. In future work we will explore how much of the remaining overprediction is due to surface moisture and fetch limitations.

ACS Style

Gerben Ruessink; Christian Schwarz; Pam Hage; Yvonne Smit; Winnie De Winter; Jasper Donker. Predicting Potential Aeolian Sand Supply to a High and Steep Foredune. 2018, 1 .

AMA Style

Gerben Ruessink, Christian Schwarz, Pam Hage, Yvonne Smit, Winnie De Winter, Jasper Donker. Predicting Potential Aeolian Sand Supply to a High and Steep Foredune. . 2018; ():1.

Chicago/Turabian Style

Gerben Ruessink; Christian Schwarz; Pam Hage; Yvonne Smit; Winnie De Winter; Jasper Donker. 2018. "Predicting Potential Aeolian Sand Supply to a High and Steep Foredune." , no. : 1.

Research article
Published: 30 August 2018 in Earth Surface Processes and Landforms
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The moisture content ws of the beach surface strongly controls the availability of sand for aeolian transport. Our predictive capability of the spatiotemporal variability in ws, which depends to a large extent on water table depth, is, however, limited. Here we show that water table fluctuations and surface moisture content observed during a 10‐day period on a medium‐grained (365 μm) planar (1:30) beach can be predicted well with the non‐linear Boussinesq equation extended to include runupinfiltration and a soil water retention curve under the assumption of hydrostatic equilibrium. On the intertidal part of the beach the water table is observed and predicted to continuously fall from the moment the beach surface emerges from the falling tide to just before it is submerged by the incoming tide. We find that on the lower 30% of the intertidal beach the water table remains within 0.1 to 0.2 m from the surface, and that the sand is always saturated (ws ≈ 20%, by mass). Higher up on the intertidal beach, the surface can dry to about 5% when the water table has fallen to 0.4 to 0.5 m beneath the surface. Above the high‐tide level the water table is always too deep (>0.5 m) to affect surface moisture and, without precipitation, the sand is dry (ws < 5 − 8%). Because the water table depth on the emerged part of the intertidal beach increases with time irrespective of whether the (ocean) tide falls or rises, we find no need to include hysteresis (wetting and drying) effects in the surface‐moisture modelling. Model simulations suggest that at the present planar beach only the part well above mean‐sea‐level can dry sufficiently (ws < 10%) for sand to become available for aeolian transport.

ACS Style

Laura B. Brakenhoff; Yvonne Smit; Jasper J. A. Donker; Gerben Ruessink. Tide-induced variability in beach surface moisture: Observations and modelling. Earth Surface Processes and Landforms 2018, 44, 317 -330.

AMA Style

Laura B. Brakenhoff, Yvonne Smit, Jasper J. A. Donker, Gerben Ruessink. Tide-induced variability in beach surface moisture: Observations and modelling. Earth Surface Processes and Landforms. 2018; 44 (1):317-330.

Chicago/Turabian Style

Laura B. Brakenhoff; Yvonne Smit; Jasper J. A. Donker; Gerben Ruessink. 2018. "Tide-induced variability in beach surface moisture: Observations and modelling." Earth Surface Processes and Landforms 44, no. 1: 317-330.

Journal article
Published: 15 November 2016 in Hydrology
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Understanding hillslope runoff response to intense rainfall is an important topic in hydrology, and is key to correct prediction of extreme stream flow, erosion and landslides. Although it is known that preferential flow processes activated by macropores are an important phenomena in understanding runoff processes inside a hillslope, hydrological models have generally not embraced the concept of an extra parameter that represents ‘macropores’ because of the complexity of the phenomenon. Therefore, it is relevant to investigate the influence of macropores on runoff processes in an experimental small artificial hillslope. Here, we report on a controlled experiment where we could isolate the influence of macropores without the need for assumptions regarding their characteristics. Two identical hillslopes were designed, of which one was filled with artificial macropores. Twelve artificial rainfall events were applied to the two hillslopes and results of drainage and soil moisture were investigated. After the experiments, it could be concluded that the influence of macropores on runoff processes was minimal. The S90 sand used for this research caused runoff to respond fast to rainfall, leading to little or no development of saturation near the macropores. In addition, soil moisture data showed a large amount of pendular water in the hillslopes, which implies that the soil has a low air entry value, and, in combination with the lack of vertical flow, could have caused the pressure difference between the matrix and the macropores to vanish sooner and result in equilibrium being reached in a relatively short time. Nevertheless, a better outline is given to determine a correct sand type for these types of experiments and, by using drainage recession analysis to investigate the influences of macropores on runoff, heterogeneity in rainfall intensity can be overcome. This study is a good point of reference to start future experiments from concerning macropores and hillslope hydrology.

ACS Style

Yvonne Smit; Martine J. Van Der Ploeg; Adriaan J. Teuling. Rainfall Simulator Experiments to Investigate Macropore Impacts on Hillslope Hydrological Response. Hydrology 2016, 3, 39 .

AMA Style

Yvonne Smit, Martine J. Van Der Ploeg, Adriaan J. Teuling. Rainfall Simulator Experiments to Investigate Macropore Impacts on Hillslope Hydrological Response. Hydrology. 2016; 3 (4):39.

Chicago/Turabian Style

Yvonne Smit; Martine J. Van Der Ploeg; Adriaan J. Teuling. 2016. "Rainfall Simulator Experiments to Investigate Macropore Impacts on Hillslope Hydrological Response." Hydrology 3, no. 4: 39.