Flow–stress coupled permeability tensor for fractured rock masses

In this paper a new analytical model is proposed to determine the permeability tensor for fractured rock masses based on the superposition principle of liquid dissipation energy. This model relies on the geometrical characteristics of rock fractures and the corresponding fracture network, and demonstrates the coupling effect between fluid flow and stress/deformation. This model empirically considers the effect of pre‐peak shear dilation and shear contraction on the hydraulic behavior of rock fractures and can be used to determine the applicability of the continuum approach to hydro‐mechanical coupling analysis. Results of numerical analysis presented in this paper show that the new model can effectively describe the permeability of fractured rock masses, and can be applied to the coupling analysis of seepage and stress fields. Copyright © 2008 John Wiley & Sons, Ltd.     

Geospatial modeling of Brown oak (<Emphasis Type="Italic">Quercus semecarpifolia</Emphasis>) habitats in the Kumaun Himalaya under climate change scenario

The study explores the use of multiple criteria decision techniques in predicting spatial niche of Brown oak (also known as Kharsu oak, Quercus semecarpifolia Sm.) formation in midaltitude (2,400–3,500 meter amsl) Kumaun Himalaya. Predictive models using various climatic and topographical factors influencing Brown oak’s growth and survival were developed to define its current ecological niche. Analytical Hierarchical Process (AHP) method involving Saaty’s pair-wise comparison was performed to rank the explanatory powers of each compared variable. Variables were suitably weighted using fuzzy factor standardization scheme to reflect their relative importance in defining species niche. An optimum indicator was then chosen for deriving a site suitability map of brown oak. This study establishes the role of aspect in the current distribution of the species along with known influence of altitude. Future niches of oak has been tracked in the projected climate change scenario of +1°C and +2°C rise in temperature and 20 mm in precipitation. The results show that on predicted +1°C and +2°C increase in temperature, present habitat of brown oak distribution may be reduced by 40 per cent and 76 per cent respectively.     

Chrome-diopside Megacryst-bearing Lamprophyre from the Late Cretaceous Mundwara Alkaline Complex,NW India: Petrological and Geodynamic Implications

The occurrence of a rare mantle-derived chrome-diopside megacryst (～8 mm), containing inclusions of olivine, in a lamprophyre dyke from the late Cretaceous polychronous (～100 – 68 Ma) Mundwara alkaline complex of NW India is reported. The olivine inclusions are forsteritic (Fo: 85.23) in composition, and their NiO (0.09 wt%) and CaO (0.13 wt%) contents imply derivation from a peridotitic mantle source. The composition of the chrome diopside (Cr₂O₃: 0.93 wt ) (Wo_45.27 En_48.47 Fs_5.07 and Ac_1.18) megacryst is comparable to that occurring in the garnet peridotite xenoliths found in diamondiferous kimberlites from Archaean cratons. Single pyroxene thermobarometry revealed that this chrome diopside megacryst was derived from a depth range of ～100 km, which is relatively much deeper than that of the chrome-diopside megacrysts (～40–50 km) reported in spinellherzolite xenoliths from the alkali basalts of Deccan age (ca. 66–67 Ma) from the Kutch, NW India. This study highlights that pre- Deccan lithosphere, below the Mundwara alkaline complex, was at least ～100 km thick and, likely, similar in composition to that of the cratonic lithosphere.     

Palaeobiology of Mesoproterozoic Salkhan Limestone, Semri Group, Rohtas, Bihar, India: Systematics and significance

Mesoproterozoic (∼ 1600 Ma old) Salkhan Limestone (Semri Group) of the Vindhyan Supergroup, exposed in Rohtas district of Bihar, India, preserves an abundant and varied ancient microbial assemblage. These microfossils are recorded in three distinctly occurring cherts viz., bedded chert, stromatolitic chert and cherty stromatolites. 27 morphoforms belonging to 14 genera and 21 species have been recognized. Six unnamed forms are also described. The microbial assemblage, almost exclusively composed of the remnants of cyanobacteria, is dominated by entophysalidacean members and short trichomes and can be termed as ‘typical Mesoproterozoic microbiotas’. The assemblage includes characteristic mat-forming scytonematacean and entophysalidacean cyanobacteria.Eoentophysalis is the dominant organism in the assemblage. Ellipsoidal akinetes of nostocalean cyanobacteria(Archaeollipsoides) and spherical unicells also occur; both are distinct from mat forming assemblage, allochthonous and possibly planktic. Co-occurrence of the microbiotas and precipitates is related to the depositional environment of the Mesoproterozoic tidal flats with high carbonate saturation.     

A semi-empirical method for predicting hydrological drought magnitudes in the Canadian prairies

Abstract

A hydrological drought magnitude (M _T ) expressed in standardized terms is predicted on annual, monthly and weekly time scales for a sampling period of T years in streamflow data from the Canadian prairies. The drought episodes are considered to follow the Poisson law of probability and, when coupled with the gamma probability distribution function (pdf) of drought magnitude (M) in the extreme number theorem, culminate in a relationship capable of evaluating the expected value, E(M _T ). The parameters of the underlying pdf of M are determined based on the assumption that the drought intensity follows a truncated normal pdf. The E(M _T ) can be evaluated using only standard deviation (σ), lag-1 autocorrelation (ρ) of the standardized hydrological index (SHI) sequence, and a weighting parameter Φ (ranging from 0 to 1) to account for the extreme drought duration (L _T ), as well as the mean drought duration (L_m ), in a characteristic drought length (L_c ). The SHI is treated as standard normal variate, equivalent to the commonly-used standardized precipitation index. A closed-form relationship can be used for the estimation of first-order conditional probabilities, which can also be estimated from historical streamflow records. For all rivers, at the annual time scale, the value of Φ was found equal to 0.5, but it tends to vary (in the range 0 to 1) from river to river at monthly and weekly time scales. However, for a particular river, the Φ value was nearly constant at monthly and weekly time scales. The proposed method estimates E(M _T ) satisfactorily comparable to the observed counterpart. At the annual time scale, the assumption of a normal pdf for drought magnitude tends to yield results in close proximity to that of a gamma pdf. The M _T , when transformed into deficit-volume, can form a basis for designing water storage facilities and for planning water management strategies during drought periods.

Editor D. Koutsoyiannis; Associate editor C. Onof

Citation Sharma, T.C. and Panu, U.S., 2013. A semi-empirical method for predicting hydrological drought magnitudes in the Canadian prairies. Hydrological Sciences Journal, 58 (3), 549–569.     

Gravitational instability for some astrophysical systems

The gravitational instability of an infinite homogeneous self-gravitating mixture through porous medium in the presence of a variable horizontal magnetic field varying in vertical directions has been considered to include, separately, the effects due to suspended particles and collisions between ionized and neutral components. The dispersion relations in both cases have been obtained. It has been found that Jeans's criterion of instability holds good even if the effects due to suspended particles, collisions, porosity, and variable magnetic field are considered.     

Assessment of different topographic corrections in AWiFS satellite imagery of Himalaya terrain

The influence of topographic effects in optical satellite imagery is not investigated very extensively in the Himalayan terrain. The topographic variability causes a problem of differential illumination due to steep and varying slopes in rugged Himalayan terrain. Therefore, topographic corrections are essential for qualitative and quantitative analysis of snow cover applications. The present paper discusses the implementation of different topographic correction models on AWiFS sensor onboard IRS P6 satellite images and the qualitative and quantitative comparative analysis in detail. Both the Lambertian and non-Lambertian assumptions have been considered in the present analysis with the aim to explore best suitable empirical model for rugged terrain. The main topographic methods implemented are:

Mapping of waterlogged areas and salt affected soils in the IGNP command area

Visual interpretation of IRS LISS-II data authenticated by ground truth was carried out for detection of waterlogged areas and characterization of salt-affected soils. The deep blue tone depicting surface ponding (stagnant ponded zone) resulted from the seepage and accumulation of irrigation water through the course sandy mass. Such unit was mostly confined to the localized low-lying areas. These data have also revealed interdunal seepage lake within the buried paleo-channel of Saraswati possibly due to submerging of excess Ghaggar floodwater. Flood irrigation, sandy soils, cultivation of high water requirement crops and presence of hard gypsiferrous pans in the shallow depths were responsible for development of waterlogged conditions in the area. The grey to yellowish white patch around the waterlogging features represented surface salt efflorescence. The grey to greyish red represented the potential waterlogging zone. Based on the analytical data, soils were characterized as moderate to highly saline and showed the presence of significant amount of CaCO₃ (>2 mm) throughout the solum. The chemical analysis of water samples revealed the presence of high to very high quantity of soluble salts dominated by chlorides and sulfates of sodium, calcium and magnesium.