Sand Dune Migration Research Articles

Morphometric analysis of slipface processes of an aeolian dune: Implications for grain‐flow dynamics

AbstractGrain flows are an integral part of sand dune migration; they are a direct response to the local wind regime and reflect complex interactions between localized over‐steepening of a dune slipface and complex turbulent airflow on the lee slope. Grain flows are primarily responsible for delivering sediment to the base of a dune, thus driving slipface advancement; yet, there are few constraints on their morphological and spatial characteristics or the amount of sediment that is redistributed by these flows. Using a combination of high‐resolution terrestrial laser scanning and video recordings, four distinct grain‐flow types are identified based on morphology and area on a dune slipface. Grain‐flow morphologies range from small, superficial flows to larger flows that affect greater portions of the slipface, moving significant amounts of sediment. Detailed field observations are presented of the dynamics of lee slopes, including measurements of the initiation location, thickness, magnitude and frequency statistics of grain flows, as well as volume estimates of redistributed sediment for each grain flow observed. High‐resolution laser scans enable accurate quantification of bulk sediment transfer from individual grain flows and can be used to study grain flows in a variety of environments. A categorization of grain‐flow morphologies is presented that links styles of flows with wind strength and direction, turbulent airflow, sediment deposition and environment.

Dune mobility in the St. Anthony Dune Field, Idaho, USA: Effects of meteorological variables and lag time

The St. Anthony Dune Field (SADF) is a ~300 km2 expanse of active to stabilized transverse, barchan, barchanoid, and parabolic sand dunes located in a semi-arid climate in southeastern Idaho. The northeastern portion of the SADF, ~16 km2, was investigated to examine meteorological influences on dune mobility. Understanding meteorological predictors of sand-dune migration for the SADF informs landscape evolution and impacts assessment of eolian activity on sensitive agricultural lands in the western United States, with implications for semi-arid environments globally. Archival aerial photos from 1954 to 2011 were used to calculate dune migration rates which were subsequently compared to regional meteorological data, including temperature, precipitation and wind speed. Observational analyses based on aerial photo imagery and meteorological data indicate that dune migration is influenced by weather for up to 5–10 years and therefore decadal weather patterns should be taken into account when using dune migration rates as proxies from climate fluctuation. Statistical examination of meteorological variables in this study indicates that 24% of the variation of sand dune migration rates is attributed to temperature, precipitation and wind speed, which is increased to 45% when incorporating lag time.

Investigating the human response to the medieval climate anomaly in the Nebraska Sand Hills: A preliminary study in building occupation histories with OSL dating

Multiple periods of dune activation triggered by drought have occurred within the Nebraska Sand Hills, the most recent period occurred during the medieval climate anomaly (MCA; A.D. 900–1350). We present a pilot study where we have successfully adapted a standard chronology-building tool, optically stimulated luminescence dating, to investigate the effects of dune reactivation on human occupation history at two sites conventionally dated to the peri-MCA: Kelso (25HO23), a Plains Woodland site, and McIntosh (25BW15) a Central Plains tradition site. At both sites the maximum optical age of the cultural layer is congruent with radiocarbon ages of materials recovered. The optical ages yielded by samples collected near the Kelso and McIntosh sites, together with radiocarbon dated site materials, suggest that these sites were respectively occupied before and during the MCA sand dune migration. Both the Kelso and McIntosh sites are located near prominent water resources that may have acted as refuges during drought and dune migration.

Modelling the interaction of aeolian and fluvial processes with a combined cellular model of sand dunes and river systems

Aeolian and fluvial processes are important agents for shaping the surface of the Earth, but are largely studied in isolation despite there being many locations where both processes are acting together and influencing each other. Using field data to investigate fluvial-aeolian interactions is, however, hampered by our short length of record and low temporal resolution of observations. Here we use numerical modelling to investigate, for the first time, the interplay between aeolian (sand dunes) and fluvial (river channel) processes. This modelling is carried out by combining two existing cellular models of aeolian and fluvial processes that requires considerable consideration of the different process representation and time stepping used. The result is a fully coupled (in time and space) sand dune – river model. Over a thousand-year simulation the model shows how the migration of sand dunes is readily blocked by rivers, yet aeolian processes can push the channel downwind. Over time cyclic channel avulsions develop indicating that aeolian action on fluvial systems may play an important part in governing avulsion frequency, and thus alluvial architecture.

A GIS add-in for automated measurement of sand dune migration using LiDAR-derived multitemporal and high-resolution digital elevation models

Desert environment modeling involving sand dune migration is important for better understanding of Earth and planetary surface processes. This paper presents a geographic information system (GIS) add-in for automated measurement of dune migration directions and migration rates using multitemporal, high-resolution digital elevation models (DEM) derived from light detection and ranging (LiDAR) data or other sources. Using the angle of repose (AOR) as a sensitive movement indicator of barchan (crescent-shaped) and transverse dunes, an add-in toolbar for ArcGIS was developed using the Python programming language to automatically detect, measure, and store dune migration direction and migration rate at random point locations on dune slip face centerlines. Pseudo-code and application samples from the White Sands dune field in New Mexico, USA, are also presented. The free add-in can be used by the geoscience community for studying coastal and desert sand dunes.[1][1] [1]: #fn-1

Using Landsat Images and Spectral Mixture Analysis to Assess Drivers of 21‐Year LULC Changes in Sudan

AbstractLandsat images acquired in 1987, 1999 and 2008 were selected to evaluate land use and land cover changes in three different ecological zones in the Republic of the Sudan: savannah (North Kordofan), semi‐desert (River Nile) and desert (Northern State). Maps of soil, vegetation and non‐photosynthetic material were built by spectral mixture analysis using endmembers spectra derived from images. Multitemporal comparison techniques were then applied to vegetation and soil maps to estimate the long‐term land degradation/re‐growth dynamics and to emphasize land cover variation over time and in space. Multitemporal comparisons have shown that site‐specific interactions between natural processes, climate variation and human activity played a pivotal role in land use and land cover change. In savannah, human activities strongly affected degradation phenomena. Expansion of villages triggered a change in land use and mismanagement of the natural resources, mainly caused by deforestation to supply wood for domestic uses. The degradation then promoted sand encroachment and dune migration. On average, 48% of the total area was subjected to medium (25–50%) and high (50–75%) land degradation. Differently, climatic constraints drove increasing degradation processes in semi‐desert and desert zones. The phenomenon was particularly severe in the desert zone. In each site, an inversion of the general trend was due to a land use change where forestry or agricultural projects were established, partly sustained in savannah by the positive rainfall trend of the last two decades. Site‐specific strategies that take into account the interactions of the driving factors at local scale are thus necessary to combat land degradation. Copyright © 2016 John Wiley & Sons, Ltd.

Acoustic observations of near‐bed sediment concentration and flux statistics above migrating sand dunes

AbstractA coherent Doppler profiler was used to measure coincident time series of velocity (u,w), sediment mass concentration (c), and sediment grain size (d), above mobile sand dunes in unidirectional flow (∼1 m/s, ∼1 m water depth). The measurements are used to extract statistical distributions of sediment concentration and flux just above the bed. Observed mass fluxes (uc,wc) were well fit by quasi‐exponential distributions, at all positions along the dune profile, similar to previous observations of single‐particle momenta for bed load over flat beds. Observed concentrations of moving particles were well fit by negative‐binomial distributions, also similar to previous observations over flat beds. These probability distributions relate to two recent stochastic theories, previously derived and verified for uniform flow over flat beds. It is hypothesized that these theories may also be used as a local approximation in natural‐scale flows with bed forms.

Genesis, distribution and dynamics of lagoon marl extrusions along the Curonian Spit, southeast Baltic Coast

A unique geological process of extrusion of lagoon marl from beneath massive migrating sand dunes is characteristic for large segments of the Curonian Spit – a ~100‐km‐long sandy barrier that separates the Curonian Lagoon from the Baltic Sea. Exposures of a composite set of Holocene organic sediments such as gyttja, clayey gyttja and gyttja clay, collectively referred to as ‘lagoon marl’, are common along the northern half of the lagoon coast of the spit. The marl outcrops rise up to 3–4 m above the lagoon level and owe their origin to extrusion from their 7–8 m in situ depth beneath the present regional water table. New detailed investigations of the Baltic Sea bottom along the southern half of the Curonian Spit using side‐scan sonar, a multibeam echosounder, seismic imaging, sediment sampling and video observations allowed identification and mapping of a unique underwater landscape formed by extensive outcrops of laminated and folded lagoon marl at water depths of 5–15 m. The combined onshore–offshore database indicates that relict lagoon marl was deformed, compacted and dehydrated by a massive dune‐covered coastal barrier migrating landward (retrograding) over these sediments during the Littorina Sea transgression in a processes termed ‘dune tectonics’. Spatial analysis of the relict sediments traced in offshore geophysical data helped to constrain the rates of the southeast migration of the dune massif. A conceptual model is presented to explain the present context of marl exposures above the regional water table, as well as the occurrence of relict lagoon marl extrusions (diapirs) on the underwater marine slope of the Curonian Spit.

Recent environmental history of the desert oasis lakes at Ounianga Serir, Chad

The Sahara desert oasis of Ounianga Serir in northern Chad comprises seven shallow but perennial lakes, which are maintained against an extremely negative local moisture balance by continuous inflow of fossil groundwater from the Nubian Sandstone Aquifer. Here we analyze the lithostratigraphy, charcoal, and fossil mollusks in short, dated sediment cores from three of these lakes (Edem, Hogou, and Agouta) to assess the hydrological and environmental stability of these unique aquatic ecosystems over the last few centuries. Our results indicate that the studied lakes remained relatively stable and fresh over the past 200–600 years, confirming the dominant and constant nature of groundwater input, preventing desiccation. Modest lake-level fluctuations did occur but were not synchronous between the lakes, arguing against climate variability being their primary cause. Likely, their site-specific history was determined by variations in groundwater through-flow, influenced by migration of sand dunes separating the lakes. The desert setting is responsible for characteristic lacustrine sediments comprised of carbonate mud with silt and sand. The associated fossil assemblages of freshwater mollusks suggest that the present-day mollusk fauna of Ounianga Serir may be more species-rich than previously thought. Our data expand the known distribution of the Palaearctic snail Valvata nilotica markedly south and westward into the central Sahara.

Analysis of Desert Sand Dune Migration Patterns from Landsat Image Time Series for The Southern California Desert

Developers of renewable energy installations in southern California need to evaluate the risks to facility operations from proximity to active desert dunes. This study first validated Landsat image spectral data using ground-based data collection of aeolian sand migration rate measurements surveyed in Arizona as an accurate method for characterizing dune mobility. The predominant direction of measured sand dune movements was correctly mapped at this site from the satellite imagery, as well as the migration distances of the leading edges of sand dunes over the entire 1992-2010 monitoring period. Application of the Landsat image method to two dune systems in southern California demonstrated its usefulness for mapping sand migration patterns and rates. Between 1995 and 2014, Palen Dunes lost over half of its stable dune surface and increased its sand accumulation zone by nearly that same area coverage. In contrast, changes in the sand movement patterns at Kelso Dunes were not apparent, perhaps due in to its more constraining mountain landscape features. These results have an immediate application for understanding future sand transport and characterizing potential impacts to nearby utility-scale solar energy installations.

Comparison of two Satellite Imaging Platforms for Evaluating Sand Dune Migration in the Ubari Sand Sea (Libyan Fazzan)

Abstract. Sand dunes can change location, form or dimensions depending on wind direction and strength. Sand dune movements can be effectively monitored through the comparison of multi-temporal satellite images. However, not all remote sensing platforms are suitable to study sand dunes. This study compares coarse (Landsat) and fine (Worldview) resolution platforms, specifically focussing on sand dunes within the Ubari Sand Sea (Libya). Sand dune features (crest line, dune ridge basal outlines) were extracted from Landsat and Worldview 2 imagery in order to construct geomorphic maps. These geomorphic maps were then compared using image overlay and differencing, and the Root Mean Squared Error (RMSE) was used to determine if the mapped dune patterns were significantly different. It was found that Landsat is a sufficient data source when studying dune patterns within a regional sand sea, but smaller dunes identified from Worldview data were not capable of being extracted in the data sourced from Landsat. This means that for studies concerned with the dune patterns and movements within sand seas, Landsat is sufficient. But in studies where the specific dynamics of specific dunes are required, a finer resolution is required; platforms such as Worldview are needed in order to gain more detailed insight and to link the past and present day climate and environmental change.

Experimental evidence for turbulent sediment flux constituting a large portion of the total sediment flux along migrating sand dunes

AbstractAccurate estimation of sediment transport is critical for many fluvial processes but remains challenging due to high‐frequency dynamics. Using novel acoustic flow instrumentation, we quantified the contribution of turbulent bed and suspended sediment fluxes to the total sediment fluxes along an entire dune profile and over the full flow depth. We found that over the dune stoss side and in the bed load layer, the turbulent mean streamwise flux is negative and reaches up to 40% of the total mean streamwise flux. Over the lee side, where turbulent intensities are highest, the contribution of the turbulent mean streamwise flux to the total mean streamwise flux is larger and reaches up to 50%. The mean vertical turbulent flux along the entire dune bed and in the bed load layer reaches nearly 30% of the total mean vertical flux. Turbulent sediment flux may thus constitute a large component of the total flux.

Bed load and suspended load contributions to migrating sand dunes in equilibrium

Dunes dominate the bed of sand rivers and are of central importance in predicting flow roughness and water levels. The present study has focused on the details of flow and sediment dynamics along migrating sand dunes in equilibrium. Using a recently developed acoustic system (Acoustic Concentration and Velocity Profiler), new insights are obtained in the behavior of the bed and the suspended load transport along mobile dunes. Our data have illustrated that, due to the presence of a dense sediment layer close to the bed and migrating secondary bedforms over the stoss side of the dune toward the dune crest, the near-bed flow and sediment processes are significantly different from the near-bed flow and sediment dynamics measured over fixed dunes. It was observed that the shape of the total sediment transport distribution along dunes is mainly dominated by the bed load transport, although the bed load and the suspended load transport are of the same order of magnitude. This means that it was especially the bed load transport that is responsible for the continuous erosion and deposition of sediment along the migrating dunes. Whereas the bed load is entirely captured in the dune with zero transport at the flow reattachment point, a significant part of the suspended load is advected to the downstream dune depending on the flow conditions. For the two flow conditions measured, the bypass fraction was about 10% for flow with a Froude number (Fr) of 0.41 and 27% for flow with Froude number of 0.51. This means that respectively 90% (for the Fr = 0.41 flow) and 73% (for the Fr = 0.51 flow) of the total sediment load that arrived at the dune crests contributed to the migration of the dunes.

Assessment of the planimetric morphology of barchan dunes

Migration of sand dunes is accounted as one of the most important natural disasters in arid and desert regions. In this study, high resolution images are combined with field measurements in order to quantitatively study the migration and long term changes in the shape and morphology of barchans. The results indicated a power correlation between height and width of barchans (R2≈0.93). It also indicated that the outline of barchans can approximately be described by a parabola. Besides, the focal length, the curvatures (windward, leeward) and the brink parabola of the barchans were calculated; using differential geometry and mathematical modeling. Surprisingly, there was no significant difference between focal length and mean curvature of barchan parabola from 2001 to 2011 (p-value>0.05). It seems the general shape of the studied barchans has not changed for long periods of time. The minimum and the maximum annual displacements of the barchans were 9 and 22m, respectively, in the study area. It was also demonstrated that the best morphologic estimators for migration rate of dunes are in this order: width, mean curvature of windward parabola and height, focal length of windward parabola, and length.

A new expression describing the migration of aeolian dunes

Based on quantitative simulations on the formation and evolution of aeolian dune fields, a semi-analytical equation describing the migration of aeolian sand dunes with respect to dune height, annual wind regime, frictional wind speed, and sand grain diameter is proposed in this paper through analyzing the migration speeds of aeolian sand dunes with different heights in a dune field. The migration speeds of aeolian sand dunes on Earth predicted by the equation is consistent with field observations, and it can be applied to describe the migration of underwater sand dunes and aeolian snow dunes on Earth, as well as that of aeolian sand dunes on other planets, for example Martian sand dunes. In addition, we can also obtain the annual wind regime and the frictional wind speed in dune fields by the A–W method proposed by this paper for given dune speed and sand diameter. It provides a new way to obtain the information of wind field in desert hinterland and on other planets.

Dunes on planet Tatooine: Observation of barchan migration at the Star Wars film set in Tunisia

Sand dune migration is documented with a readily-available tool (Google Earth) near Chott El Gharsa, just north-west of Tozeur, Tunisia. As fiducial markers we employ a set of buildings used to portray the fictional city Mos Espa. This set of ~20 buildings over roughly a hectare was constructed in 1997 for the movie Star Wars Episode 1 — The Phantom Menace. The site now lies between the arms of a large “pudgy” barchan dune, which has been documented via satellite imaging in 2002, 2004, 2008 and 2009 to have moved from ~140m away to only ~10m away. Visits by the authors to the site in 2009 and 2011 confirm the barchan to be in a threatening position: a smaller set nearby was substantially damaged by being overrun by dunes circa 2004. The migration rate of ~15m/yr decreases over the observation period, possibly as a result of increased local rainfall, and is consistent with barchan migration rates observed at other locations worldwide. The migration rate of this and two other barchans suggests sand transport of ~50m3/m/yr, somewhat higher than would be suggested by traditional wind rose calculations: we explore possible reasons for this discrepancy. Because of the link to popular science fiction, the site may be of pedagogical interest in teaching remote sensing and geomorphic change. We also note that nearby playa surfaces and agricultural areas have a time-variable appearance. The site's popularity as a destination for Star Wars enthusiasts results in many photographs being posted on the internet, providing a rich set of in-situ imagery for continued monitoring in the absence of dedicated field visits.

Tracking sand dune migration in the Rub Al-Khali with ICESat laser altimetry

Sand dune migration poses serious environmental and social problems for both the infrastructure and communities in the Saudi Arabian Peninsula. In order to monitor and better understand dune migration, a new method is proposed to estimate sand dune displacement/migration by using satellite laser altimetry data from the ICESat mission in the Rub Al-Khali. This method will exploit not only the differences in the observed ICESat elevation profiles, but also the phase differences between two co-located tracks when observed at different times. By using the phase differences, the proposed method will be able to estimate dune displacement vectors with an accuracy of 5 m root mean square. This accuracy has been validated using synthetic data with known displacements. The major causes for dune migration are the wind regime and the type of dunes (e.g. grain size and vegetation cover). A comparison of estimated dune displacement correlated well with the prevailing wind regime during the observation time period. A comparison with satellite imagery revealed that the dune shape and direction (i.e. the representative parameters of dune migration) are in agreement with the estimated displacement vectors. This method represents one of the first attempts to monitor dune migration using space observations only.

A new GIS-based model for automated extraction of Sand Dune encroachment case study: Dakhla Oases, western desert of Egypt

The movements of the sand dunes are considered as a threat for roads, irrigation networks, water resources, urban areas, agriculture and infrastructures. The main objectives of this study are to develop a new GIS-based model for automated extraction of sand dune encroachment using remote sensing data and to assess the rate of sand dune movement. To monitor and assess the movements of sand dunes in Dakhla oases area, multi-temporal satellite images and a GIS-developed model, using Python script in Arc GIS, were used. The satellite images (SPOT images, 1995 and 2007) were geo-rectified using Erdas Imagine. Image subtraction was performed using spatial analyst in Arc GIS, the result of image subtraction obtains the sand dune movement between the two dates. The raster and vector shape of sand dune migration was automatically extracted using spatial analyst tools. The frontiers of individual dunes were measured at different dates and movement rates were analyzed in GIS. The ModelBuilder in Arc GIS was used in order to create a user friendly tool. The custom built model window is easy to handle by any user who wishes to adapt the model in his work. It was found that the rate of sand dune movement ranged between 3 and 9m per year. The majority of sand dunes have a rate movement between 0 and 6m and very few dunes had a movement rate between 6 and 9m. Integrating remote sensing and GIS provided the necessary information for determining the minimum, maximum, mean, rate and area of sand dune migration.

Influence of Gas-Liquid Two-Phase Intermittent Flow on Hydraulic Sand Dune Migration in Horizontal Pipelines

This paper presents an experimental study of three-phase flows (air-water-sand) inside a horizontal pipe. The results obtained aim to enhance the fundamental understanding of sand transportation due to saltation in the presence of a gas-liquid two-phase intermittent flow. Sand dune pitch, length, height, and front velocity were measured using high-speed video photography. Four flow compositions with differing gas ratios, including hydraulic conveying, were assessed for sand transportation, having the same mixture velocity. For the test conditions under analysis, it was found that the gas ratio did not affect the average dune front velocity. However, for intermittent flows, the sand bed was transported further downstream relative to hydraulic conveying. It was also observed that the slug body significantly influences sand particle mobility. The physical mechanism of sand transportation was found to be discontinuous with intermittent flows. The sand dune local velocity (within the slug body) was measured to be three times higher than the averaged dune velocities, due to turbulent enhancement within the slug body.

Anatomy and sedimentary model of a hooked spit (Sylt, southern North Sea)

A sedimentary model for hooked spit depositional systems based on ground-penetrating radar and sedimentological data is presented. The recurved main spit of Sylt Island (southern North Sea) is dominated by migrating sand dunes; the investigated hooked spit exhibits a system of foredune ridges, oriented perpendicular to the dunes of the recurved spit. The development of the hooked spit is related closely to the presence of an adjacent tidal inlet, where strong tidal currents and a steep bathymetry prevent a further northward progradation of the main spit and trigger a deflection from northerly-directed to easterly-directed net sediment transport. Ground-penetrating radar data and shallow sediment cores reveal the sedimentary architecture of the hooked spit in high resolution and allow the proposition of a genetic stratigraphic model. It is shown that the growth of the hooked spit is controlled by the interplay of alongshore migrating foreshore beach drifts under fair-weather conditions and strong erosional events, interpreted as the result of rare severe storms. These storms may excavate scarps in the backshore, which play an important role in the development of foredune ridges. Accelerator mass spectrometry 14C ages indicate an absolute age of at least 1300 years for the hooked spit, which possibly correlates with strengthened erosion of the main spit. In contrast to the main spit, where the sediment budget is negative nowadays, growth of the hooked spit beach accelerated significantly during the last decades. This effect can probably be attributed to enhanced beach-nourishments updrift along the main spit and makes the investigated hooked spit a natural laboratory to study the influence of increasing sediment supply into a system developing under the conditions of sea-level rise. The study shows that the same external forces lead to distinct progradational processes along one barrier-spit system.