Width variations control the development of grain structuring in steep step-pool dominated streams: insight from flume experiments

We report results from flume experiments designed to study the effect of width variations on the formation and stability of steps in steep streams. To physically model channel width changes we inserted multiple trapezoidal elements in the flume. Two competing effects are in play: a fluidic effect, suggesting that steps are more likely to form in wide areas because of deposition enhanced by lower shear stress, and a granular effect, suggesting that steps are more likely to form in narrow areas because of particle jamming. Our experiments show that width variations enhance the formation of steps. Although steps can form in every location, those in narrow/narrowing areas are more common, more stable and they occupy a larger portion of the channel width. These results stress the importance of particle interactions in coarse-bedded streams and help river engineers by providing a new element to consider when designing step-pool sequences in river restoration projects. © 2020 John Wiley & Sons, Ltd.     

Assessment of the potential of semi-arid plants to reduce soil erosion in the Konartakhteh watershed,Iran

Soil erosion is a major environmental problem in arid and semi-arid areas. Although bioengineering is important in preventing soil erosion, plant architecture and mechanical properties in these areas are rarely studied. In this study, in order to evaluate the potential of native plants to reduce soil erosion in semi-arid regions, their above-ground (e.g., stem density, radius of the stem, etc.) and below-ground (e.g., root area ratio, root tensile strength, etc.) characteristics were measured in the field and laboratory. Five indicators, namely, stem density (SD), sediment obstruction potential (SOP), plant stiffness (MEI), relative soil detachment (RSD), and root cohesion (Cr), were taken into account. Each indicator was scored according to a five-point scale (0?=?low, 4?=?high), and then, the score of each indicator was represented on an ameba diagram. Finally, for understanding traits of plants and evaluating their potential to control rill and gully erosion, the area occupied by the ameba diagram was studied. The results indicated that the shrub Ziziphus spina-christi (MEI?=?108.35 N, RSD?=?0.398, Cr?=?8.34 kPa, SOP?=?0.097, and SD?=?0.00270) is a very suitable native plant species for controlling both the gully and rill erosion. In addition, Scariola orientalis is effective for sediment obstruction, but its low scores on the MEI and RSD indicators imply that it is not able to control gully development. Furthermore, Noaea mucronata, Platychaete glaucescens, Astragalus gummifer, Alhagi persarum, Lycium shawii, and Prosopis farcta have a distinct potential to reduce the rate of gully erosion. These results have wide applicability for adopting soil conservation measures to other semi-arid environments.     

Behaviour of Track Ballast Under Repeated Loading

Najaf-sea quarry is located in Najaf city about 160 km south west of Baghdad the capital of Iraq. It is the main source that supplies track ballast for maintenance of existing railway network and construction of new railway lines in the middle and southern parts of Iraq. Track ballast experience a complex combination of stresses during its service lifetime, primarily from repeated axial loads of the trains in addition to stresses generated from the environmental conditions. The ideal evaluation of suitability of track ballast must be carried out under real field loading conditions, however such field tests are usually costly and time consuming. On the other hand laboratory model tests simulating field loads under limited boundary conditions can provide satisfactory indication about the suitability of the material. The present paper investigates the deformation characteristics of Najaf-sea track ballast, under repeated loading using model tests simulating ballast conditions under a selected track section. A test setup was designed and manufactured capable of applying both monotonic as well as repeated loading on the track section under different conditions. The repeated model tests which simulate as close as possible the field conditions shed the light on the generated settlement, modulus of deformation and degradation of the ballast particles under different repeated loading levels. Statistical analysis in terms of breakage index and repeated applied load revealed satisfactory correlations that help in understanding the overall performance of the ballast material. The results also demonstrate that 4–5 tamping are capable of controlling both the settlement and modulus of deformation of the ballast material.     

Monitoring rangeland ground cover vegetation using multitemporal MODIS data

The aim of the present research is to monitor changes in herbage production during the grazing season in the Semirom and Brojen regions, Iran, using multitemporal Moderate Resolution Imaging Spectroradiometer (MODIS) data. At first, various preprocessing steps were applied to a topography map. The atmospheric and topographic corrections were applied using subtraction of the dark object method and the Lambert method. Image processing, including false-color composite, principal component analysis, and vegetation indices were employed to produce land use and pasture production maps. Vegetation sampling was carried out over a period of 4 months during June–September 2008, using a stratified random sampling method. Twenty random sampling points were selected, and herbage production was estimated and verified with the double-checking method. Four MODIS data sets were used in this study. The models for image processing and integrating ground data with satellite images were processed, and the resulting images were categorized into seven classes. Finally, the land covers were verified for accuracy. A postclassification analysis was carried out to verify the seven class change detections. The results confirmed that Normalized Difference Vegetation Index (NDVI) and Soil-Adjusted Vegetation Index (SAVI) maps had a close relationship with the field data. The indices produced with shortwave infrared bands had a close relationship with field data where the ground cover and yields were high. The R ² value observed was 0.85. The changes in the pasture vegetation were high during the growing season in more than 90 % of the pastures. During the growing season, most changes in the pastures belonged to class 5 and 2 in the NDVI and SAVI index maps, respectively.     

Comparison of split window algorithms to derive land surface temperature from satellite TIRS data

Remote sensing data can be used as the basis for meteorological data. Due to the limitations of meteorological stations on the Earth, derivation of land surface temperature is one of the most important aspects of the remote sensing application in climatology studies. In the present study, Landsat-8 thermal infrared sensor data of the scene located over Khuzestan province with row/path of 165/38 were used to derive land surface temperature (LST). Normalized difference vegetation index (NDVI), fraction of vegetation cover, satellite brightness temperature, and land surface emissivity were calculated as the vital criteria to derive LSTs using the split window algorithms. LST determination was performed by nine different split window algorithms. Eventually, LST products were evaluated using ground-based measurements at the meteorological stations of the study area. The results showed that algorithm of Coll and Casselles had a highest accuracy with RMSE 1.97 °C, and Vidal’s method presented the lowest accuracy to derive LST with RMSE 4.11 °C. According to the results, regions with high density of vegetation and water resources have lowest diurnal temperature and regions with bare soils and low density of vegetation have a highest diurnal temperature. Results of the study indicated that LST algorithm accuracy is an important factor in the environmental and climate change studies.     

Geology and geochemistry of Tertiary basalt in south Wadi Hodein area, South Eastern Desert, Egypt

Tertiary basalt is widespread in the area south of Wadi Hodein, south Eastern Desert, Egypt. It is the youngest unit in the basement rocks of the Central Eastern Desert classification of El Shazly (Proc 22nd Intl Geol Congr, New Delhi 10:88–101, 1964) and El Ramly (Ann Geol Surv Egypt II:1–17, 1972), traversed all the previous succession of the basement rocks as well as the Nubia Sandstone of Cretaceous age, forming sheets, small hills, ridges, and dikes. This Tertiary basalt is strongly associated with the opening of the Red Sea. Geologic, petrographic, and petrochemical studies as well as microprobe and X-ray analyses were performed on samples from Wadi Hodein Tertiary basalt. Field and petrographic studies classified the Tertiary basalt in south Wadi Hodein into porphyritic olivine basalt, plagiophyric basalt, and doleritic basalt. Opaque minerals (magnetite and ilmenite) constitute 6–7.5% of this basalt. Petrochemical studies and microprobe analyses reveal that they are low-TiO₂ basalt with low uranium and thorium contents, classified as being basaltic andesite to andesite, originated from calc-alkaline magma, and developed in within-plate tectonic environment. Scanning electron microscopy shows that magnetite and ilmenite are the prevalent opaque minerals in this Tertiary basalt. Field radiometric measurements of the Tertiary basalt in south Wadi Hodein reveals low uranium and thorium contents. Uranium contents range from 0.5 to 0.9 ppm, while thorium contents range from 1.2 to 3.2 ppm. Fractional crystallization and mass balance modeling indicate that the most-silica low-TiO₂ Tertiary basalt in south Wadi Hodein can be derived from the relatively less-silica low-TiO₂ Tertiary basalt of south Quseir and Gabal Qatrani through fractional crystallization of plagioclase, olivine, augite, and titanomagnetite oxides. Tertiary basalts in south Wadi Hodein and south Quseir have nearly the same age, 25 Ma (Sherif, The Fifth International Conference on the Geology of Africa, 2007), 24 Ma (Meneisy and Abdel Aal, Ain Shams Sci Bull 25(24B): 163–176, 1984), and 27 Ma (El Shazly et al., Egypt J Geol 1975), respectively. Finally, the fractionation modeling and geochemical characteristics of these basalts suggested their origination from one basaltic magma emplaced in late Oligocene.     

Application of plurigaussian simulation to delineate the layout of alteration domains in Sungun copper deposit

An accurate estimation of mineral grades in ore deposits with heterogeneous spatial variations requires defining geological domains that differentiate the types of mineralogy, alteration and lithology. Deterministic models define the layout of the domains based on the interpretation of the drill holes and do not take into account the uncertainty in areas with fewer data. Plurigaussian simulation (PGS) can be an alternative to generate multiple numerical models of the ore body, with the aim of assessing the uncertainty in the domain boundaries and improving the geological controls in the characterization of quantitative attributes. This study addresses the application of PGS to Sungun porphyry copper deposit (Iran), in order to simulate the layout of four hypogene alteration zones: potassic, phyllic, propylitic and argillic. The aim of this study is to construct numerical models in which the alteration structures reflect the evolution observed in the geology.     

Hydrodynamic efficiency improvement of the High Skew Propeller for the underwater vehicle under surface and submerged conditions

An algorithm based on the Boundary Element Method(BEM)is presented for designing the High Skew Propeller(HSP)used in an Underwater Vehicle(UV).Since UVs operate under two different kinds of working conditions(i.e.surface and submerged conditions),the design of such a propeller is an unwieldy task.This is mainly due to the fact that the resistance forces as well as the vessel efficiency under these conditions are significantly different.Therefore,some factors are necessary for the design of the opti-mum propeller to utilize the power under the mentioned conditions.The design objectives of the optimum propeller are to obtain the highest possible thrust and efficiency with the minimum torque.For the current UV,the main dimensions of the propeller are pre-dicted based on the given required thrust and the defined operating conditions.These dimensions(number of blades,pitch,diameter,expanded area ratio,thickness and camber)are determined through iterative procedure.Because the propeller operates at the stern of the UV where the inflow velocity to the propeller is non-uniform,a 5-blade HSP is preferred for running the UV.Finally,the propel-ler is designed based on the numerical calculations to acquire the improved hydrodynamic efficiency.