Temporal and spatial variabilities in the surface moisture content of a fine-grained beach

Namikas, Steven L.; Edwards, Brandon L.; Bitton, M.C.A.; Booth, Jennifer; Zhu, Yongnan

doi:10.1016/j.geomorph.2009.07.011

Cited by 46 publications

(56 citation statements)

References 19 publications

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“…It illustrates the overall increase in moisture content from the dunefoot to the waterline, with superimposed variability related to secondary morphological highs and lows, consistent with [21]. The map also shows two narrow, approximately alongshore bands of apparent lower moisture content, which correspond to car tracks.…”

Section: Resultssupporting

confidence: 65%

Measuring and Modeling the Effect of Surface Moisture on the Spectral Reflectance of Coastal Beach Sand

et al. 2014

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Surface moisture is an important supply limiting factor for aeolian sand transport, which is the primary driver of coastal dune development. As such, it is critical to account for the control of surface moisture on available sand for dune building. Optical remote sensing has the potential to measure surface moisture at a high spatio-temporal resolution. It is based on the principle that wet sand appears darker than dry sand: it is less reflective. The goals of this study are (1) to measure and model reflectance under controlled laboratory conditions as function of wavelength () and surface moisture () over the optical domain of 350–2500 nm, and (2) to explore the implications of our laboratory findings for accurately mapping the distribution of surface moisture under natural conditions. A laboratory spectroscopy experiment was conducted to measure spectral reflectance (1 nm interval) under different surface moisture conditions using beach sand. A non-linear increase of reflectance upon drying was observed over the full range of wavelengths. Two models were developed and tested. The first model is grounded in optics and describes the proportional contribution of scattering and absorption of light by pore water in an unsaturated sand matrix. The second model is grounded in soil physics and links the hydraulic behaviour of pore water in an unsaturated sand matrix to its optical properties. The optical model performed well for volumetric moisture content 24% ( 0.97), but underestimated reflectance for between 24–30% ( 0.92), most notable around the 1940 nm water absorption peak. The soil-physical model performed very well ( 0.99) but is limited to 4% 24%. Results from a field experiment show that a short-wave infrared terrestrial laser scanner ( = 1550 nm) can accurately relate surface moisture to reflectance (standard error 2.6%), demonstrating its potential to derive spatially extensive surface moisture maps of a natural coastal beach.

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Section: Resultssupporting

confidence: 65%

Measuring and Modeling the Effect of Surface Moisture on the Spectral Reflectance of Coastal Beach Sand

et al. 2014

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“…As such, foredunes are unique aeolian features affected by dynamic interactions between a host of marine, terrestrial, biotic, and atmospheric processes (Bauer & Sherman, ; Hesp & Walker, ; Sherman & Bauer, ; Walker et al, ). Foredunes may be large or small, continuous or discontinuous, and permanent or ephemeral features of the coastline depending on a host of controls such as (1) vegetation type and growth rate (Hacker et al, ; Keijsers et al, ); (2) plant density and distribution (Hesp, ); (3) presence of roughness elements (e.g., woody debris, vegetation wrack, foot prints, and coarse lag deposits) (Bauer et al, ; Eamer & Walker, ; Grilliot et al, ; Nordstrom et al, ; Walker & Barrie, ); (4) nature of sand supply (Aagaard et al, ; Bauer & Davidson‐Arnott, ; R Davidson‐Arnott & Bauer, ; Delgado‐Fernandez & Davidson‐Arnott, ; Hoonhout & de Vries, ; Nickling & Davidson‐Arnott, ; de Vries et al, ; de Vries et al, ); (5) moisture conditions, especially with respect to the sand surface (Anthony et al, ; Bauer et al, ; Davidson‐Arnott et al, ; de Vries et al, ; Ellis & Sherman, ; Namikas et al, ; Smit et al, ); (6) fetch or distance across which the wind blows before reaching the foredune (Bauer et al, ; Bauer & Davidson‐Arnott, ; Delgado‐Fernandez et al, ; Jackson & Cooper, ); and (7) airflow and sand transport interactions with beach‐dune topography (Hesp et al, ; Lynch et al, ; Walker et al, ; Walker et al, ).…”

Section: Introductionmentioning

confidence: 99%

The Role of Large Woody Debris in Beach‐Dune Interaction

2019

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Coastal foredune evolution involves complex processes and controls that result from the interaction of aeolian and nearshore dynamics. No studies to date have quantified and examined the role of large woody debris (LWD) as a modulator of sediment delivery across the backshore and as a control on foredune development and maintenance. Results from a 4‐year research initiative on a high‐energy, macrotidal beach, and foredune system show that storm events lead to wave‐induced erosion of the backshore and consequent reworking of the LWD matrix. The exposed LWD matrix subsequently traps wind‐blown sand on the upper beach, reducing sediment delivery to the foredune by 99% in some cases. In turn, deposition within the LWD matrix leads to rapid burial of the LWD, at least until the next reworking or dune erosion event occurs. Interannual observations at this site indicate that infilling of the accommodation space within the LWD matrix can be rapid, so sediment starvation of the foredune is typically a relatively short‐lived phase. This suggests that that the LWD matrix is a highly effective, yet ephemeral, sand‐trapping reservoir. Critical to these interactions is the frequency and magnitude of nearshore events that erode the beach periodically and reorganize the LWD matrix, which directly impacts the ability of LWD to modulate onshore sand transport to the foredune, store sediment in the backshore, and act as a buffer against erosive events. An empirically derived conceptual model explaining these relationships is presented.

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“…Bauer and Davidson‐Arnott, 2003; Davidson‐Arnott et al ., 2008; Bauer et al ., 2009; Davidson‐Arnott and Bauer, 2009; Hesp et al ., 2009; Walker et al ., 2009a; Walker et al ., 2009b). Yet, it remains an elusive and poorly constrained physical attribute that contributes to difficulties in successfully applying predictive sediment transport models (Namikas et al ., 2010).…”

Section: Introductionmentioning

confidence: 99%

“…The high degree of spatial and temporal variability of surface moisture can confound traditional measurement techniques [such as soil moisture probes and gravimetric measurements (Wiggs et al ., 2004b; Yang and Davidson‐Arnott, 2005)] that rely on ‘spot‐based’ sampling. Whilst soil moisture probeshave proven to be very useful in elucidating the variability of surface moisture over the complete intertidal and back beach area (Oblinger and Anthony, 2008; Edwards and Namikas, 2009; Anthony et al ., 2009; Namikas et al ., 2010), their volumetric measurement technique means that they struggle to take account of the smaller‐scale moisture variations where sharp, near‐surface gradients in moisture content exist. They are therefore not ideal for determining moisture properties of a thin veneer of surface particles (Darke et al ., 2009), and it is this surface moisture content which sediment entrainment and transport is most sensitive to.…”

Section: Introductionmentioning

confidence: 99%

Aeolian sand strip mobility and protodune development on a drying beach: examining surface moisture and surface roughness patterns measured by terrestrial laser scanning

Nield

Wiggs

Squirrell

2010

Earth Surf Processes Landf

117

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Ephemeral aeolian sand strips are commonplace on beaches. Their formation during high energy sand transport events often precedes the development of protodunes and their dynamics present interesting feedback mechanisms with surface moisture patterns. However, due to their temporary nature, little is known of their formation, mobility or the specifics of their interaction with beach surface characteristics. Similarly surface moisture has an important influence on sediment availability and transport in aeolian beach systems, yet it is difficult to quantify accurately due to its inherent variability over both short spatial and temporal scales. Whilst soil moisture probes and remote sensing imagery techniques can quantify large changes well, their resolution over mainly dry sand, close to the aeolian transport threshold is not ideal, particularly where moisture gradients close to the surface are large. In this study we employed a terrestrial laser scanner to monitor beach surface moisture variability during a three and a half hour period after a rain event and investigated relationships between bedform development, surface roughness and surface moisture. Our results demonstrate that as the beach surface dries, sand transport increases, with sediment erosion occurring at the wet/dry surface boundary, and deposition further downwind. This dynamic structure, dependent upon changing surface moisture characteristics, results in the formation of a rippled sand strip and ultimately a protodune. Our findings highlight dynamic mobility relationships and confirm the need to consider transient bedforms and surface moisture across a variety of scales when measuring aeolian transport in beach settings. The terrestrial laser scanner provides a suitable apparatus with which to accomplish this.

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Temporal and spatial variabilities in the surface moisture content of a fine-grained beach

Cited by 46 publications

References 19 publications

Measuring and Modeling the Effect of Surface Moisture on the Spectral Reflectance of Coastal Beach Sand

Measuring and Modeling the Effect of Surface Moisture on the Spectral Reflectance of Coastal Beach Sand

The Role of Large Woody Debris in Beach‐Dune Interaction

Aeolian sand strip mobility and protodune development on a drying beach: examining surface moisture and surface roughness patterns measured by terrestrial laser scanning

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