Mobile Sand Research Articles

Where Does Titan Sand Come From: Insight From Mechanical Properties of Titan Sand Candidates

AbstractExtensive equatorial linear dunes exist on Titan, but the origin of the sand, which appears to be organic, is unknown. We used nanoindentation to study the mechanical properties of a few Titan sand candidates, several natural sands on Earth, and common materials used in the Titan Wind Tunnel, to understand the mobility of Titan sand. We measured the elastic modulus (E), hardness (H), and fracture toughness (Kc) of these materials. Tholin's elastic modulus (10.4 ± 0.5 GPa) and hardness (0.53 ± 0.03 GPa) are both an order of magnitude smaller than silicate sand, and it is also smaller than the mechanically weak white gypsum sand. With a magnitude smaller fracture toughness (Kc = 0.036 ± 0.007 MPa·m1/2), tholin is also much more brittle than silicate sand. This indicates that Titan sand should be derived close to the equatorial regions where the current dunes are located, because tholin is too soft and brittle to be transported for long distances.

Environmental and economic importance of native plants and green belts in controlling mobile sand and dust hazards

The prevailing and strong north-westerly wind in Kuwait during summer is consistently causing a significant movement of aeolian sediment that poses serious environmental and economic threats. The average removal costs per cubic metre for aeolian encroachments around desert infrastructures in Kuwait increased from USD 1.2 to USD 1.32, respectively, representing one of the highest expenses in the region in 1993 and 2013. Correspondingly, morphological properties of aeolian deposits around 15 dominant species of native plants were determined, after which, the cost saving per plant was calculated equivalent to the cubic metre removal cost. Nitraria retusa, Lycium shawii, Haloxylon salicornicum, and Calligonum polygonoides trapped the maximum mobile aeolian sediments up to 21.9, 15.5, 14.5, and 13.3 m3, respectively, which make them the most efficient solutions for present and future applications in controlling aeolian processes. Aeolian activities were monitored during the establishment stage of 110,000 of these effective native plants in the Liyah protected area and green belts of Moringa pterygosperma in the Kabd area. It was noted that native plants had a positive effect as they captured about 115 t of aeolian sediments, thus saving USD 151800 as estimated removal cost of these accumulations all around human settlements. Native plants and green belts have also contributed to the reduction in the annual rates of mobile sand by 94 and 95.3%, and dust by 64.5 and 68.4%, respectively.

Afforestation with xerophytic shrubs accelerates soil net nitrogen nitrification and mineralization in the Tengger Desert, Northern China

Afforestation with xerophytic shrubs in drylands to curb desertification and land degradation has been increasingly implemented worldwide. However, the effects of this restoration practice on soil nitrogen mineralization and availability in desert areas remain poorly understood. We investigated the seasonal patterns of soil inorganic N pools and net N nitrification and mineralization in mobile sand dune and three shurblands (afforested in 1956, 1964 and 1981, respectively) in the Tengger Desert by using the in situ incubation method. Our results showed that afforestation significantly increased the soil inorganic N pools, and net nitrification and mineralization rates. Annual average values of NH4+-N, NO3−-N and total inorganic N were 2.64–4.06, 3.37–7.74 and 3.06–6.12 times greater in afforested sites that those in mobile sand dunes, with NO3−-N being predominated in all sites and its proportion being increased with stand age. In mobile sand dune, annual soil net N nitrification and mineralization rates were 1.25 and 1.87 mg N m−2 d−1, respectively, while those in afforested sites were 5.32–11.89 and 5.98–15.16 times higher, respectively, with nitrification predominated the N mineralization process. Marked seasonality in inorganic N pools, net N nitrification and mineralization were observed with the highest values in summer and the lowest in winter, which were closely linked to afforestation-induced changes in soil temperature and moisture as well as surface litter, content of clay and silt, C: N and OC of soil. The contrasting results for soil N transformations were observed during non-growing season, that was net N immobilization for the mobile sand dune without afforestation and the shrubland established in 1981, while net N mineralization for the shrublands established in 1964 and 1956, the latter two sites account for 2.65% and 9.68% of their total mineralization, respectively. These results suggested that afforestation with xerophytic shrubs has positive effects on soil nitrogen availability and cycling in desert region. It also implied that the afforestation-triggered recovery of biogeochemical cycling of N was a long-term process, and therefore soil habitat conservation is a vital issue in desert ecosystems.

Dinâmica Sedimentar das Dunas Transgressivas do Sistema Laguna-Barreira da Costa Sul de Moçambique, África

Transgressive dunes are very common in the southeastern coastal region of Africa. They have the potential to yield important information about regional winds, sediment supply and their response to sea-level fluctuations during the Holocene.The regional climatic patterns and the wind dynamics of the transgressive dunes associated with the barrier lagoon system of southern Mozambique were studied. Rainfall record, wind regime and atmospheric temperature records were analysed, complemented by annual monitoring of transgressive dune progradation. Data obtained suggest that the coastal dunes associated to lagoon-barrier system are mostly controlled by the southeast quadrant wind regime and annual rainfall indexes of about 1600mm. The combination of the sediment transport potential estimated at ~ 46 kg/m/s with sand mobility of ~200, resulted in the intense silting process on the lacustrine and lagoon systems. The application of mathematical models of sedimentary dynamics permitted the identification of two distinctive morphological characteristics of dunefields including active and semi-vegetated dunes on the southern area (Maputo Province), and semi-vegetated and fixed dunes on the northern area (Gaza Province), Mozambique - Africa.

RESEARCH AND APPLICATION OF REMOTE SENSING MONITORING METHOD FOR DESERTIFICATION LAND UNDER TIME AND SPACE CONSTRAINTS

Abstract. Serious land desertification and sandified threaten the urban ecological security and the sustainable economic and social development. In recent years, a large number of mobile sand dunes in Horqin sandy land flow into the northwest of Liaoning Province under the monsoon, make local agriculture suffer serious harm. According to the characteristics of desertification land in northwestern Liaoning, based on the First National Geographical Survey data, the Second National Land Survey data and the 1984–2014 Landsat satellite long time sequence data and other multi-source data, we constructed a remote sensing monitoring index system of desertification land in Northwest Liaoning. Through the analysis of space-time-spectral characteristics of desertification land, a method for multi-spectral remote sensing image recognition of desertification land under time-space constraints is proposed. This method was used to identify and extract the distribution and classification of desertification land of Chaoyang City (a typical citie of desertification in northwestern Liaoning) in 2008 and 2014, and monitored the changes and transfers of desertification land from 2008 to 2014. Sandification information was added to the analysis of traditional landscape changes, improved the analysis model of desertification land landscape index, and the characteristics and laws of landscape dynamics and landscape pattern change of desertification land from 2008 to 2014 were analyzed and revealed.

Deep soil water recharge response to precipitation in Mu Us Sandy Land of China

Soil water is the main form of water in desert areas, and its primary source is precipitation, which has a vital impact on the changes in soil moisture and plays an important role in deep soil water recharge (DSWR) in sandy areas. This study investigated the soil water response of mobile sand dunes to precipitation in a semi-arid sandy area of China. Precipitation and soil moisture sensors were used to simultaneously monitor the precipitation and the soil water content (SWC) dynamics of the upper 200-cm soil layer of mobile sand dunes located at the northeastern edge of the Mu Us Sandy Land of China in 2013. The data were used to analyze the characteristics of SWC, infiltration, and eventually DSWR. The results show that the accumulated precipitation (494 mm) from April 1 to November 1 of 2013 significantly influenced SWC at soil depths of 0–200 cm. When SWC in the upper 200-cm soil layer was relatively low (6.49%), the wetting front associated with 53.8 mm of accumulated precipitation could reach the 200-cm deep soil layer. When the SWC of the upper 200-cm soil layer was relatively high (10.22%), the wetting front associated with the 24.2 mm of accumulated precipitation could reach the upper 200-cm deep soil layer. Of the accumulated 494-mm precipitation in 2013, 103.2 mm of precipitation eventually became DSWR, accounting for 20.9% of the precipitation of that year. The annual soil moisture increase was 54.26 mm in 2013. Accurate calculation of DSWR will have important theoretical and practical significance for desert water resources assessment and ecological construction.

Scale Invariance of Power Spectrum in Sediment Transport Mechanics

Flume experiments were carried over a curvilinear mobile sand bed and over a vegetated sand bed to scale the power spectra variation in the longitudinal velocity spectrum of turbulence flow. Instantaneous three dimensional velocities were sampled using an acoustic Doppler velocimeter; sequentially spectral analysis of the filtered velocities is consummated. Results depict that slope of power spectra is varying with the variation of wave number, consequently three different ranges obtained for power spectrum, where spectrum scaling is confined to some particular range according to low, intermediate and high wave numbers.

Factors influencing the natural regeneration of the pioneering shrub Calligonum mongolicum in sand dune stabilization plantations in arid deserts of northwest China.

Calligonum mongolicum is a successful pioneer shrub to combat desertification, which is widely used for vegetation restoration in the desert regions of northwest China. In order to reveal the limitations to natural regeneration of C. mongolicum by asexual and sexual reproduction, following the process of sand dune stabilization, we assessed clonal shoots, seedling emergence, soil seed bank density, and soil physical characteristics in mobile and stabilized sand dunes. Controlled field and pot experiments were also conducted to assess germination and seedling emergence in different dune soil types and seed burial depths. The population density of mature C. mongolicum was significantly different after sand dune stabilization. Juvenile density of C. mongolicm was much lower in stabilized sand dunes than mobile sand dune. There was no significant difference in soil seed bank density at three soil depths between mobile and stabilized sand dunes, while the emergence of seedlings in stabilized dunes was much lower than emergence in mobile dunes. There was no clonal propagation found in stabilized dunes, and very few C. mongolicum seedlings were established on stabilized sand dunes. Soil clay and silt content, air‐filled porosity, and soil surface compaction were significantly changed from mobile sand dune to stabilized dunes. Seedling emergence of C. mongolicm was highly dependent on soil physical condition. These results indicated that changes in soil physical condition limited clonal propagation and seedling emergence of C. mongolicum in stabilized sand dunes. Seed bank density was not a limiting factor; however, poor seedling establishment limited C. mongolicum's further natural regeneration in stabilized sand dunes. Therefore, clonal propagation may be the most important mode for population expansion in mobile sand dunes. As a pioneer species C. mongolicum is well adapted to propagate in mobile sand dune conditions, it appears unlikely to survive naturally in stabilized sand dune plantations.

Assessment of the Aeolian sand dynamics in the region of Ain Sefra (Western Algeria), using wind data and satellite imagery

The region of Ain Sefra is an arid region suffering from sand encroachment. In this study, we are calculating the shifted sand quantity and efficient wind directions during a period of 30 years (1985 to 2015) in order to classify the danger. The study shows that efficient winds in the region are characterized by their potential drift estimated at 220 till 329. This classifies the region as medium. Besides, the resultant drift potential is 76 to 99 with a migration coefficient of 0.3 which gives a medium classification to the zone and proves the Aeolian erosion complex system and its interrelation with other factors. Efficient winds generally blow from South-west to North-east with an angle of 234°. Furthermore, there are other directions causing sand drifting. Sand movement quantity is estimated between 23.03 and 15,224 m3/m/year according to effective wind threshold speed, which is 5 to 6 m/s. Autumn is the period when sand mobility is higher, but it decreases in winter. On the other hand, sand potential movement was well shown through satellite imagery between 1985 and 2015. Indeed, it closely corresponded to the previous study. It showed sand movement direction from South-west to North-east, and sand surface increase reached 16.44% of the global zone surface. Whereas, it decreased − 2.5% between 1985 and 2015. There is an important concentration of sand accumulation under the western mountain foothills along which sand moves. This shows that the ground particularities play a crucial role in this phenomenon.

Doñana mobile dunes: what is the vegetation pattern telling us?

In coastal dunes, changes in plant composition and vegetation pattern can reveal processes such as plant succession, dune stabilization or reactivation. With that goal, I sampled plant species composition, topography and sand mobility along 4 parallel transects perpendicular to the coastline in the mobile dune system of Donana. I used Split Moving Window to locate boundaries between plant communities along transects. To assess the main trends in variation, data of plant cover from all transects were subject to multivariate ordination analysis. Plant composition and geomorphological traits allowed to distinguish several stretches along all transects. Multivariate analyses reflected two different trends, plant succession and dune stabilization. High cover of Halimium halimifolium in the primary dune slack was consistent with the lack of new deposits of fresh sand. Growth of pine trees facilitated the colonization of the dune tail by H. halimifolium in a positive feedback. Although several studies have pointed out a decrease in the advance rates of dunes due to an increase in plant cover, the present results suggest that the increase in plant cover in the outer dunes is due to the stabilization of the secondary dune. Therefore, vegetation pattern evidenced a process of dune stabilization, which may produce loss of original plant communities and heterogeneity of dune landscapes.

On the 30th Anniversary of the “General Plan to Combat Desertification of Black Lands and Kizlyar Pastures”

This paper reviews the main historical stages of the development and implementation of the largest environmental project of the late 20th century—the “General Plan to Combat Desertification of Black Lands and Kizlyar Pastures.” The goal of this project was to implement a scientifically grounded set of measures to stop desertification processes, improve the economic state of pastures, increase their fertility, and protect lands. The implementation of the general plan has led to the performance of agroforestry works in an area of more than 7000 km2, the fixing of more than 4000 km2 of mobile sands, and the restoration of more than 2500 km2 of pastures. According to the forecasts, if all of the measures stipulated by the general plan were observed, the area of the ecological disaster zone would decrease and then completely disappear. A study conducted with Landsat satellite images showed that this forecast has partially come true: the area of open sands that was recorded in the test plot in 2016 (27.3 km2) is only 1% of the open sands area recorded in 1975, which is a consequence of the implementation of the general plan, a number of environmental measures, and favorable climate fluctuations.

Morphological description and DNA barcoding study of sand rice (Agriophyllum squarrosum, Chenopodiaceae) collected in Kazakhstan

BackgroundSand rice (Agriophyllum squarrosum (L.) Moq.) is an annual shrub-like plant adapted to the mobile sand dunes in desert and semi-desert regions of Asia. It has a balanced nutrient composition with relatively high concentration of lipids and proteins, which results in its nutrition being similar to legumes. Sand rice’s proteins contain the full range of essential amino acids. However, calories content is more similar to wheat. These features together with desert stress resistance make sand rice a potential food crop resilient to ongoing climate change. It is also an important fodder crop (on young stages of growth) for cattle in arid regions of Kazakhstan. In our work, sand rice samples were collected from two distant regions of Kazakhstan as a part of the nation-wide project to determine genetic variation of the native flora.ResultsSamples were collected in western and southeastern parts of Kazakhstan separated by distances of up to 1300 km. Sequences of the nuclear ribosomal DNA ITS1-5.8S-ITS2 region and the chloroplast matK gene confirmed the identity of species defined by morphological traits. Comparison with GenBank sequences revealed polymorphic sequence positions among Kazakh populations and GenBank references, and suggested a distinction among local populations of sand rice. The phylogenetic analysis of nucleotide sequences showed a clear partition of A. squarrosum (L.) Moq. from Agriophyllum minus Fisch. & C.A. Mey, which grows in the same sand dunes environment.ConclusionsDNA barcoding analyses of ITS and matK sequences showed a segregation of A. squarrosum from A. minus into separate clades in Maximum-Likelhood dendrograms. ITS analysis can be successfully used to characterize A. squarrosum populations growing quite distant from each other. The data obtained in this work provide the basis for further investigations on A. squarrosum population structure and may play a role in the screening of sand rice plants growing in desert and semi-desert environments of Central Asia and China.

Is annual recharge coefficient a valid concept in arid and semi-arid regions?

Abstract. Deep soil recharge (DSR) (at depth greater than 200 cm) is an important part of water circulation in arid and semi-arid regions. Quantitative monitoring of DSR is of great importance to assess water resources and to study water balance in arid and semi-arid regions. This study used a typical bare land on the eastern margin of Mu Us Sandy Land in the Ordos Basin of China as an example to illustrate a new lysimeter method of measuring DSR to examine if the annual recharge coefficient is valid or not in the study site, where the annual recharge efficient is the ratio of annual DSR over annual total precipitation. Positioning monitoring was done on precipitation and DSR measurements underneath mobile sand dunes from 2013 to 2015 in the study area. Results showed that use of an annual recharge coefficient for estimating DSR in bare sand land in arid and semi-arid regions is questionable and could lead to considerable errors. It appeared that DSR in those regions was influenced by precipitation pattern and was closely correlated with spontaneous strong precipitation events (with precipitation greater than 10 mm) other than the total precipitation. This study showed that as much as 42 % of precipitation in a single strong precipitation event can be transformed into DSR. During the observation period, the maximum annual DSR could make up 24.33 % of the annual precipitation. This study provided a reliable method of estimating DSR in sandy areas of arid and semi-arid regions, which is valuable for managing groundwater resources and ecological restoration in those regions. It also provided strong evidence that the annual recharge coefficient was invalid for calculating DSR in arid and semi-arid regions. This study shows that DSR is closely related to the strong precipitation events, rather than to the average annual precipitation, as well as the precipitation patterns.

Resilience of Sandhills Grassland to Wildfire During Drought

In the Nebraska Sandhills, one of the largest contiguous grassland ecoregions remaining in North America, sandy textured soils are stabilized by fine root biomass from predominantly warm-season grasses. Concerns over destabilization have led to management that aims to avoid an undesirable state change toward mobile sand dunes. In 2012, the Sandhills experienced extreme drought conditions that coincided with the worst wildfire year on state record. According to state-and-transition models and ecosystem managers, the combination of wildfire and drought conditions should cause a state transition due to a lack of recovery of grassland vegetation and a loss of sand dune stability. To test this hypothesis, we implemented a time-since-fire study to track biomass recovery of Sandhills grassland vegetation following a wildfire on The Nature Conservancy’s Niobrara Valley Preserve in burned and unburned areas. Two yr following the wildfire, aboveground herbaceous biomass in burned areas had recovered to levels that did not differ from unburned areas, maintaining the stability of the sand dunes. This provides evidence that counters current land management frameworks that portray Sandhills grassland as highly vulnerable to destabilization when wildfires occur during severe drought conditions.

Development of bacterial communities in biological soil crusts along a revegetation chronosequence in the Tengger Desert, northwest China

Abstract. Knowledge of structure and function of microbial communities in different successional stages of biological soil crusts (BSCs) is still scarce for desert areas. In this study, Illumina MiSeq sequencing was used to assess the compositional changes of bacterial communities in different ages of BSCs in the revegetation of Shapotou in the Tengger Desert. The most dominant phyla of bacterial communities shifted with the changed types of BSCs in the successional stages, from Firmicutes in mobile sand and physical crusts to Actinobacteria and Proteobacteria in BSCs, and the most dominant genera shifted from Bacillus, Enterococcus and Lactococcus to RB41_norank and JG34-KF-361_norank. Alpha diversity and quantitative real-time polymerase chain reaction (PCR) analysis indicated that bacterial richness and abundance reached their highest levels after 15 years of BSC development. Redundancy analysis showed that silt + clay content and total K were the prime determinants of the bacterial communities of BSCs. The results suggested that bacterial communities of BSCs recovered quickly with the improved soil physicochemical properties in the early stages of BSC succession. Changes in the bacterial community structure may be an important indicator in the biogeochemical cycling and nutrient storage in early successional stages of BSCs in desert ecosystems.

Holocene environmental changes in the Horqin desert revealed by OSL dating and δ13C analyses of paleosols

The Horqin desert in northeastern China is located on the climatically-sensitive margin of the East Asian summer monsoon front and the paleosols in the desert potentially provide a record of environmental changes in the region. During the last two decades several paleoenvironmental studies have increased our knowledge of past shifts in the desert-grassland border in the deserts of northeastern China. However, studies of Holocene vegetation changes with high-quality age data are scarce. Here, we present the results of optically stimulated luminescence dating and analyses of magnetic susceptibility, total organic carbon and the stable carbon isotope composition of organic matter, and inferred C4 biomass, of the paleosol sequences of the Tuquan and Mutougou sections in the Horqin desert and utilize them to document Holocene environmental changes in the region. The results reveal that the East Asian summer monsoon precipitation gradually increased and previously unstable dunes were semi-stabilized from ∼11 to 9 ka. The semiarid conditions were then replaced by the more humid environment of the Holocene climatic optimum from ∼9 to 5 ka. During the Holocene climatic optimum, the paleosols in the Tuquan and Mutougou sections developed, and the percentage of C4 plants increased and the dunes in the Horqin desert were extensively stabilized. Subsequently, alternation of eolian sand mobilization and paleosol development occurred, indicating that the environment became cold and dry, with temporary wet and warm stages. Estimates of C4 biomass from the two sections demonstrate that the favorable growing conditions for C4 plants extended to at least 45°N in North China during the Holocene. We conclude that Holocene environmental changes in the Horqin desert were controlled by movements of the East Asian summer monsoon rainfall belt on a millennial time scale, and that human activity also played a significant role in environmental change during the late Holocene.

Soil bacterial community responses to revegetation of moving sand dune in semi-arid grassland.

Grasslands in semi-arid Northern China are widely desertified, thus inducing the formation of a large area of moving sand lands. Revegetation of the sandy land is commonly adopted to restore degraded grasslands. The structure of the soil microbial community might dramatically change during degradation and recovery because microorganisms are one of the major drivers of ecological process through their interactions with plants and soil. Assuming that soil properties are the key determinants of the structure of soil bacterial community within the same soil type, whether the vegetation type causes the significant difference in the structure of soil bacterial community during revegetation and restoration of the degraded grasslands remains poorly understood. Our study aimed to (1) investigate the response of soil bacterial communities to the changes during vegetation degradation and recovery and (2) evaluate whether the soil bacterial communities under plantations return to their native state. We detected the shifts in diversities and compositions of the soil bacterial communities and the relative abundance of dominant bacterial taxa by using the high-throughput Illumina MiSeq sequencing technique in an area covered by 32-year-old Caragana microphylla, Artemisia halodendron, Hedysarum fruticosum, Pinus sylvestris var. mongolica, Populus simonii, and Salix gordejevii sand-fixing plantations and in the native community (NC) dominated by elm, and moving sandy dune (MS). We found that the obtained operational taxonomic units by 16S rRNA gene sequencing and diversity index in MS were all significantly lower than those in NC, and the number and composition of dominant genera were significantly different between NC and MS. Interestingly, the compositions of bacterial communities and the dominant genera in different sand-fixation plantations (C. microphylla, A. halodendron, H. fruticosum, P. sylvestris var. mongolica, P. simonii, and S. gordejevii) were all similar to those of the native soil of NC, suggesting that the plantation type and soil properties exhibit a minimal effect on the compositions of soil microbial communities within a continuous landscape. These results revealed that the structure of the soil bacterial community of degraded sandy grassland (even degenerated into a mobile sand dunes) in semi-arid region can be reversibly restored by planting indigenous shrub or semi-shrub plantation on human time scales.

Moss-dominated biocrusts increase soil microbial abundance and community diversity and improve soil fertility in semi-arid climates on the Loess Plateau of China

Various ecological functions of biocrusts are mostly determined by their bacterial and fungal abundance and community diversity, which has not yet been fully investigated. To provide more insights into this issue, we collected samples of moss biocrusts, fixed sand, and mobile sand from a watershed with semi-arid climate on the Loess Plateau of China. The relative abundances and community diversities of soil bacteria and fungi of the samples were determined using high-throughput DNA sequencing. Finally, we analyzed the characteristics of bacterial and fungal community of the moss biocrusts and their relationships to the content of soil nutrients. Our results showed that the moss biocrusts had 1048 bacterial OTUs (operational taxonomic units) and 58 fungal OTUs, and their Shannon diversity indexes were 5.56 and 1.65, respectively. The bacterial community of the moss biocrusts was dominated by Acidobacteria (24.3%), Proteobacteria (23.8%), Chloroflexi (15.8%), and Actinobacteria (14.5%), and their fungal community was dominated by Ascomycota (68.0%) and Basidiomycota (23.8%). The moss biocrusts had far more bacterial OTUs (≥56.9%) but similar number of fungal OTUs as compared with the uncrusted soil, and their Sorenson’s similarity coefficients of bacterial and fungal communities were less than 0.768 and 0.596, respectively. Moreover, the contents of soil nutrients (C, N, P) were significantly correlated with the OTU numbers of bacteria and the relative abundances of bacteria and fungi. Our results indicated that moss biocrusts harbor a large number and high diversity of bacteria and fungi, and these diversified bacteria and fungi play important roles in ecosystem functioning through improving soil fertility.

Initiation of motion and scour burial of objects underwater

Laboratory experiments were conducted to examine mobility and burial of objects, including onset of motion on a rigid bottom, scour burial into a sand bed, and the interplay between scour and motion onset. Experiments covered a range of object diameter-to-bottom roughness ratios (D/k) of relevance to mobility of unexploded ordnance (UXO). Results indicate that the critical mobility parameter (ΘUcrit) varies as ΘUcrit ≈ 1.6(D/k)−0.72 for cylinders under currents and waves. Modifications of this relation are also presented for accelerating flows. Scour experiments produced formulae for the equilibrium burial depth (Beq) for UXO as a function of the sediment Shields parameter (Θsed) of the form Beq/D = a2 Θsedb2. For current-induced live-bed scour, relatively large cylinders (D >8cm) result in a2 ≈1.3 and b2 ≈0.36. Smaller cylinders (D <3cm) and a tapered shape bury more easily (a2 ≈15 and b2 ≈1.1). An alternate, physics based relation for Beq incorporating additional length scales is also presented. For objects on mobile sand under accelerating flow, behavior was observed to be a contest between scour burial and the current speed reaching critical mobility. It is shown that by considering pit depth at the moment of mobility to be the effective bottom roughness, a general explanation of the onset of motion can be obtained.

PROSPECTS FIXATION DRIFT SANDS PHYSICOCHEMICAL METHOD

Summary. This article is based on the theoretical foundations of secure mobile sand being considered for reducing the negative impact...