Vertical Profiles of Wind-Blown Sand Flux over Fine Gravel Surfaces and Their Implications for Field Observation in Arid Regions

We used a compact boundary layer wind tunnel equipped with a turbulence generator and a piezoelectric blown-sand meter to investigate the effects of the surface coverage of fine gravel on wind-blown sand flux. The vertical profile of wind-blown sand over a flat sand surface showed an exponential distribution at all wind speeds, whereas the profile over gravel surfaces of 20% or greater coverage showed a non-monotonic vertical distribution. At 20% to 30% gravel coverages, a peak of wind-blown sand flux developed between 6 and 10 cm above the ground at all wind speeds because of less energy loss due to grain-bed collisions at that level. To analyze the erosional state of wind-blown sand, we used the Wu–Ling index (λ) of the mass-flux density of sand-bearing wind. Values of λ for all gravel coverages were greater than 1 at all wind speeds, indicating an unsaturated (erosional) state. Moreover, we found that the wind-blown sand flux at 4 cm height accounted for about 20% of the total flux regardless of wind speed and gravel coverage. This finding can simplify future estimations of total near-surface wind-blown sand flux based on field observations because such measurements can be taken at just one height.

Incipient bedforms in a bidirectional wind regime

Most terrestrial sand seas form at ‘horse’ latitudes, where the wind direction exhibits seasonal variation. Here, we extend the two-dimensional linear stability analysis of a flat sand bed associated with a unidirectional wind to the three-dimensional case in order to account for multidirectional wind regimes. Focusing on the simplest case of bidirectional flow regimes, we show that the transition from transverse to oblique or longitudinal patterns is controlled by the transport ratio and the divergence angle between the two flows. Our predictions agree with previous results for dune orientation, and also provide a wider range of possible alignments depending on flow strength, especially when the two winds are perpendicular, at which the transition occurs. This analysis also predicts the selected pattern wavelength, which either decreases close to the transition angle for strong winds, due to a geometric effect, or increases at low winds, when the bed slope affects the transport. This theoretical analysis is complemented by analogous subaqueous experiments, where bedforms are submitted to alternate water flows. For transverse bedforms, the experimental data validate the model at strong flows, providing evidence for the predicted geometric effect, but also for the increase of the wavelength close to the transport threshold. For longitudinal bedforms, a discrepancy is observed, which we interpret as the sign of enhanced nonlinearities induced by the development of slip faces when the flow alternately blows on both sides of the dune.

BENTHIC HABITAT ON CORAL REEF ECOSYSTEM IN MENJANGAN ISLAND

Coastal ecosystems covering three important parts of mangroves, seagrass beds and coral reefs are an integral part of the habitat mapping process. This study aims to mapping habitats of the island of Menjangan in West Bali National Park (TNBB), Bali. Field data was collected in February, April and August 2017. Total 110 sampling points spread across the coastal area of Menjangan island by looking at the texture differences using the ENVI v4.7 program from satellite image data Worldview 2 October 14th 2016. The results showed that the study area is divided into 6 types of main habitat (geomorphological levels) i.e., reef front, reef slope, reef flat, Sand and Terrace on which we add the mangroves, Ground-truhing data and cross-reef photograph-transects of habitats described with with medium scale approach suggest that, on reef flat and crest areas, 12 habitats has been described. This includes coral habitat (coral>30% cover) dominated by several types of hard coral (Scleractinia) ie Acropora sp, Montipora sp, Porites lutea and Porites cylindrica; mixed with rubble and algae (mostly Chlorophyta and Phaeophyta) each covering about 15%. Sand (10-15%) and seagrasses (including Syringodium sp, Cymodocea sp and Thalassia sp) (10%) are more marginally present. The blue coral Heliopora coerulea (non Scleractinia), mixed coral associations, and dead corals complete the assemblages . On the reef flat rugosity is low (1 – 2) but increases toward the crest and front reef with rugosity level at 3 - 4. On this research it can be one of data support for re-zonation in West Bali National Park especially in Menjangan Island and surrounding area.

Exploring How Water Flow Affects Bed Forms in Different Environments

In a flat sand bed, water creates undulating features.

Bahasa Rupa Gambar Anak Berkesulitan Belajar dan Relasinya dengan Gambar Seni Rupa Tradisi

ABSTRACT Children with learning disabilities have creative capabilities that sometimes unnoticed by their pa- rents or teachers. Their creative capabilities are usually observed from their drawings, which as creative as the drawings created in traditional arts. The aim of this research is to determine the relationship between drawings from children with learning disabilities compared to the drawings created in traditional arts.The research methods employed is a qualitative descriptions with visual languages approaches. The approaches used are contents of wimba, way of wimba, enlargement and shrinkage. It can be shown that the way of drawing by children with learning disabilities has direct relationship with the traditional arts. The way of wimba of these children’s drawings is having similar characteristics with the way of wimba in traditional arts.  This similarity is observed from the unique way of drawing of these children which are figurative objects drawn on a flat sand surface, various backgrounds, various relieves, tranparencies, emphasizing large objects, green colour, and symmetrical compositions. These similarities are constructed because these children do not know about perspective drawing and gravitational principles in the draw- ing, somethings which are also found in traditional art, so that both tend to have similar way of wimba in drawings. The characteristics of drawing by children with learning disabilities can be seen from the way of wimba figures which are schematics, which should already surpassed by children with similar age. Keywords: Children, Drawings, Learning disabilities, Traditional arts, Visual language    ABSTRAK Anak berkesulitan belajar mempunyai kreativitas yang belum diketahui oleh orang tua bah- kan guru. Kreativitas yang tergali dari gambar yang dihasilkan oleh Anak Berkesulitan Belajar (ABB), sama kreatifnya dengan gambar yang berasal dari seni rupa tradisi. Penelitian ini untuk mengetahui relasi antara gambar ABB dengan gambar seni rupa tradisi. Relasi adalah hal yang membuat adanya keterhubungan antara gambar ABB dengan gambar seni rupa tradisi.Metode penelitian ini adalah deskriptif kualitatif dengan pendekatan bahasa rupa. Bahasa rupa yang dipergunakan adalah isi wimba, cara wimba, diperbesar atau diperkecil. Hasil pene- litian ini diketahui bahwa cara gambar anak memiliki relasi dengan gambar seni rupa tradisi, yaitu cara wimba gambar ABB mempunyai karakteristik kemiripan dengan gambar seni rupa tradisi. Hal tersebut dapat diamati dari cara khas gambar anak yaitu objek figur digambarkan diatas rata tanah, aneka latar, aneka tampak, tembus pandang, objek yang besar dibuat penting, warna hijau, komposisi simetris. Kemiripan tersebut karena anak-anak belum mengenal gam- bar perspektif dan gaya gravitasi pada gambar, hal yang sama juga ditemui dalam seni rupa seni tradisi sehingga mereka memiliki kecenderungan penggambaran cara wimba yang mirip. Sedangkan karakteristik gambar ABB dapat dilihat dari cara wimba figur yang menyerupai bagan, padahal untuk anak seusianya anak sudah melampaui bentuk tersebut. Kata kunci: Anak-anak, Bahasa rupa, Berkesulitan Belajar, Gambar, Seni rupa tradisi

Study on Sedimentary Facies of Carboniferous Kalashayi Formation in the South of Tahe Oilfield

Tahe Oilfield is an significant petroleum exploitation and development area in Tarim Basin for SINOPIC. Carboniferous Kalashayi Formation has become an important oil-bearing series for increasing and maintaining production, and for finding backup resource in this Oilfield. Based on the theories and methods of sedimentology, by using the sesmic, log and core data, the sedimentary facies of Carboniferous Kalashayi Formation in the south of Tahe Oilfield are analyzed deeply. Through the study of characteristics of the rock type and texture,sedimentary structure, sedimentary sequence, stratic structure, paleontology, geochemistry and geophysics of Kalashayi Formation, the Sand-shale Section is attributed to tidal flat deposits which has a nature of estuary. The study area are mainly dominated by intertidal zone, including mud flat, sand-mud flat, sand flat, tidal channel and mouth bar microfacies. The Up-mudstone Section developed lagoonal facies. This study provides favorable support for the further petroleum exploration in study area.

Bedforms in a turbulent stream: formation of ripples by primary linear instability and of dunes by nonlinear pattern coarsening

It is widely accepted that both ripples and dunes form in rivers by primary linear instability; the wavelength of the former scaling on the grain size and that of the latter being controlled by the water depth. We revisit here this problem in a theoretical framework that allows to give a clear picture of the instability in terms of dynamical mechanisms. A multi-scale description of the problem is proposed, in which the details of the different mechanisms controlling sediment transport are encoded into three quantities: the saturated flux, the saturation length and the threshold shear stress. Hydrodynamics is linearized with respect to the bedform aspect ratio. We show that the phase shift of the basal shear stress with respect to the topography, responsible for the formation of bedforms, appears in an inner boundary layer where shear stress and pressure gradients balance. This phase shift is sensitive to the presence of the free surface, and the related effects can be interpreted in terms of standing gravity waves excited by topography. The basal shear stress is dominated by this finite depth effect in two ranges of wavelength: when the wavelength is large compared to the flow depth, so that the inner layer extends throughout the flow, and in the resonant conditions, when the downstream material velocity balances the upstream wave propagation. Performing the linear stability analysis of a flat sand bed, the relation between the wavelength at which ripples form and the flux saturation length is quantitatively derived. It explains the discrepancy between measured initial wavelengths and predictions that do not take this lag between flow velocity and sediment transport into account. Experimental data are used to determine the saturation length as a function of grain size and shear velocity. Taking the free surface into account, we show that the excitation of standing waves has a stabilizing effect, independent of the details of the flow and sediment transport models. Consequently, the shape of the dispersion relation obtained from the linear stability analysis of a flat sand bed is such that dunes cannot result from a primary linear instability. We present the results of field experiments performed in the natural sandy Leyre river, which show the formation of ripples by a linear instability and the formation of dunes by a nonlinear pattern coarsening limited by the free surface. Finally, we show that mega-dunes form when the sand bed presents heterogeneities such as a wide distribution of grain sizes.