Crater formation in soils by raindrop impact

The process of crater formation by the impact of water drops on soil, sand and various other target material was studied. Craters of various shapes and sizes were observed on different target materials or conditions, ranging from circumferential depression to completely hemispherical shape. Crater shape was dependent upon target material, its ?ow stress or shear strength and the presence and thickness of water on the surface. Between 5 and 22 per cent of impact energy was spent on cratering, but the relationship between crater volume and kinetic energy of a raindrop was curvilinear, indicating a lower ef?ciency of impact energy in removing target material as the energy increases. Impact impulse, on the other hand, showed a more linear relationship with crater volume, and the ratio of impulse over crater volume (I/V) remained constant for the entire range of drop sizes, impact velocities, and surface conditions used in this study. Surface shear strength, represented by the penetration depth of fall‐cone penetrometer, appeared to be a key factor involved in this process. An equation was developed which related crater volume to cone penetration depth and impact impulse. Crater volume, which appeared to be a better indicator of the total amount of material dislodged by a raindrop than splash amount, can thus be predicted using this equation. Copyright © 2004 John Wiley & Sons, Ltd.     

Bioattenuation in groundwater impacted by landfill leachate traced with δ13C

The impact on groundwater imparted by the infiltration of high dissolved organic carbon (DOC) leachate from capped, unlined landfills can be attenuated by biogeochemical reactions beyond the waste source, although such reactive loss in the aquifer is difficult to distinguish from conservative advective dispersion. Compound-specific measurement of δ(13)C in carbon species, including CH(4), dissolved inorganic carbon (DIC), and the major DOC compounds (acetate, humic acid, and fulvic acid) provides a constraint in this assessment that can assist in exercises of modeling and prediction of leachate transport. The Trail Road municipal landfill near Ottawa, Ontario, Canada, hosts an unlined sector which produces a highly enriched leachate (DOC >4500 mg/L) that provides a good site to examine reactive attenuation within the receptor aquifer. Acetate, a sentinel component of leachate DOC (~1000 mg C/L), is absent in impacted groundwater. Mass balance calculations together with reaction modeling suggest continued acetate fermentation with calcite control on DIC and δ(13)C(DIC) evolution. In groundwater within 50 m of the landfill, methane concentrations are elevated (~10 mg/L), consistent with acetate fermentation, whereas δ(13)C(CH4) measurements in deeper groundwater range down to -51‰ compared with -60‰ in the landfill demonstrating oxidative loss. DOC in the deep aquifer is remarkably depleted to values less than -40‰ suggesting methanotrophic bacteria selectively consume isotopically light CH(4) to fix carbon. Continued reaction of leachate DOC in groundwater is demonstrated by evolution away from conservative mixing lines on diagrams of δ(13)C vs. concentrations of DIC and DOC.     

Application of integrated geoelectrical methods in Khenadarreh (Arak,Iran) graphite deposit exploration

This paper is devoted to application of SP, resistivity and mise-a-la-masse method in Khenadarreh (Arak, Iran) graphite deposit exploration. Mise-a-la-masse method is one of the main geophysical exploration methods used to investigate conductive bodies with outcrops on the surface or in exploratory pits. By integrating mise-a-la-masse results with other geoelectrical methods, such as self-potential and resistivity surveys, useful results can be acquired. Powerful survey design, data processing and interpretation methods can make geoelectrical surveying results more reliable. Here, we applied integrated geoelectrical methods to explore the Khenadarreh-bala graphite deposit in the Sarband region of the Markazi province, Iran. We present a new and simple method for processing and interpreting mise-a-la-masse data, which corrects for the effect of distance from the current electrode in the conductive body. After correction, the residual potential values corresponded with the SP results and the apparent resistivity pseudosections. The geophysical results were confirmed by drill holes in the study area.     

Investigation of rangeland indicator species using parametric and non-parametric methods in hilly landscapes of central Iran

This study aimed to identify indicator species and explore the most important environmental and management variables contributing to vegetation distribution in a hilly upper dam landscape in Zagros Mountain chain, Iran. A stratified random sampling method was used to collect topographic, edaphic, management and vegetation data. The density and cover percentage of perennial species were measured quantitatively. Indicator species were identified using the two-way indicator species analysis. Besides calculating physiognomic factors in sample sites, 24 soil samples were collected from 0 to 30 cm of soil depth and analyzed in terms of gravel percentage, texture, saturation moisture, organic matter, pH and electrical conductivity in saturation extract, lime percentage, soluble calcium and magnesium, available phosphorus, Cation Exchange Capacity(CEC) and soluble sodium and potassium. Multivariate techniques including Canonical Correspondence Analysis and Multi-Dimensional Scaling were used to explore the relationships of species with environmental and management variables. Seven plants were identified as indicator species due to being significantly correlated with management(grazing or non-grazing) and edaphic variables such as CEC, soil texture, pH, CaCO_3 percentage and physiographic variable including slope, elevation, and convex and concave formations(p 0.05). Overall, overgrazing and its subsequent effects on soil characteristics, loss of vegetation cover and trampling were found as the major causes of deterioration. Sustainable and integrated management practices such as the implementation of appropriate grazing systems were suggested to enhance soil quality and reduce the accelerated erosion in upper dam zones.     

Spatial modelling of reference evapotranspiration using adjusted Blaney-Criddle equation in an arid environment

Abstract

The Blaney-Criddle (BC) temperature-based equation is used in areas where the complete weather data to estimate reference evapotranspiration (ET₀) by the Penman-Monteith FAO-56 (PMF-56) standard model is complex. In this study, the BC equation was first tested and calibrated against the ET₀ values computed by the PMF-56 method using data from 17 weather stations in arid regions of Iran. Then, geographical information systems (GIS)-based spatially-distributed maps of ET₀ were prepared by means of geographic/topographic factors derived from a digital elevation model (DEM) for all months, separately. The results indicate that the original BC equation overestimated PMF-56 ET₀ by 4% at the study sites. The BC equation produced closer ET₀ estimates to the PMF-56 method after it was calibrated. The error rate of <3% for the spatial modelling approach suggests that the developed ET₀ maps are reliable.

Editor D. Koutsoyiannis; Associate editor D. Yang

Citation Tabari, H., Hosseinzadeh Talaee, P., and Shifteh Some'e, B., 2013. Spatial modelling of reference evapotranspiration using adjusted Blaney-Criddle equation in an arid environment. Hydrological Sciences Journal, 58 (2), 408–420.     

Documenting hurricane impacts on coral reefs using two-dimensional video-mosaic technology

Four hurricanes impacted the reefs of Florida in 2005. In this study, we evaluate the combined impacts of hurricanes Dennis, Katrina, Rita, and Wilma on a population of Acropora palmata using a newly developed video‐mosaic methodology that provides a high‐resolution, spatially accurate landscape view of the reef benthos. Storm damage to A. palmata was surprisingly limited; only 2 out of 19 colonies were removed from the study plot at Molasses Reef. The net tissue losses for those colonies that remained were only 10% and mean diameter of colonies decreased slightly from 88.4 to 79.6 cm. In contrast, the damage to the reef framework was more severe, and a large section (6 m in diameter) was dislodged, overturned, and transported to the bottom of the reef spur. The data presented here show that two‐dimensional video‐mosaic technology is well‐suited to assess the impacts of physical disturbance on coral reefs and can be used to complement existing survey methodologies.     

Scattering of plane harmonic SH,SV, P and rayleigh waves by non-axisymmetric three-dimensional canyons: A wave function expansion approach

Scattering of elastic waves by three-dimensional canyons embedded within an elastic half-space is investigated by using a wave function expansion technique. The geometry of the canyon is assumed to be non-axisymmetric. The canyon is subjected to incident plane Rayleigh waves and oblique incident SH, SV and P waves. The unknown scattered wavefield is expressed in terms of spherical wave functions which satisfy the equations of motion and radiation conditions at infinity, but they do not satisfy stress-free boundary conditions at the half-space surface. The boundary conditions are imposed locally in the least-squares sense at several points on the surface of the canyon and the half-space. Through a comparative study the validity and limitations of two-dimensional approximations (antiplane strain and plane strain models) have been examined. It is shown that scattering of waves by three-dimensional canyons may cause substantial change in the surface displacement patterns in comparison to the two-dimensional models. These results emphasize the need for three-dimensional modelling of realistic problems of interest in strong ground motion seismology and earthquake engineering.     

Comparison between Shannon and Tsallis entropies for prediction of shear stress distribution in open channels

The concept of Tsallis entropy was applied to model the probability distribution functions for the shear stress magnitudes in circular channels (with filling ratios of 0.506, 0.666, 0.826), circular with flat bed (filling ratios of 0.333, 0.666), rectangular channel (1.34, 2, 3.94, 7.37 aspect ratios) and compound channel (with relative depths of 0.324, 0.46). The equation for the shear stress distribution was obtained according to the entropy maximization principle, and is able to estimate the shear stress distribution as much on the walls as the channel bed. The approach is also compared with the predictions obtained based on the Shannon entropy concept. By comparing the two prediction models, this study highlights the application of Tsallis entropy to estimate the shear stress distribution of open channels. Although the results of the two models are similar in the circular cross-section, the differences between them are more significant in circular with flat bed and rectangular channels. For a wide range of filling ratio values, experimental data are used to illustrate the accuracy and reliability of the proposed model.     

Genesis of Tertiary Magnetite–Apatite Deposits,Southeast of Zanjan,Iran

Magnetite–apatite deposits in the Alborz volcano–plutonic belt, southeast Zanjan, in Iran, have blade, lenzoid, and vein forms, which extend in an E‐W direction. There are many magnetite–apatite veins and veinlets in this region, and some of them are economically important, such as Zaker, Morvarid, Sorkheh–Dizaj, and Aliabad. The sizes of the vein orebodies vary between 2 and 16 m in width, 10–100 m in length, and 5–40 m in depth. Microscopic examination of thin sections and polishes indicate that they are composed of magnetite and apatite, with minor amounts of goethite, hematite, actinolite, quartz, muscovite–illite, talc, dolomite, and calcite. The geochemistry and mineralogy of the granitic host rock reveals that it is calc‐alkaline and I‐type. Field observations, mineral paragenesis, the composition of the orebodies, and the composition of the fluid inclusions in the apatite minerals with low salinity (less than 20 wt.% NaCl equivalent) indicate that these magnetite veins were hydrothermally generated at about 200–430°C and are not related to silica–iron oxide immiscibility, as are the major Precambrian magnetite deposits in central Iran.