Differential behaviour of a Lesser Himalayan watershed in extreme rainfall regimes     

Pankaj Chauhan  Nilendu Singh  Devi Datt Chauniyal  Rajeev S Ahluwalia  Mohit Singhal 《Journal of Earth System Science》2017,126(2):22

Climatic extremes including precipitation are bound to intensify in the global warming environment. The present study intends to understand the response of the Tons sub-watershed in Lesser Himalaya, in 3 years with entirely different hydrological conditions (July 2008–June 2011) in terms of discharge, sediment flux and denudation rates. Within an uncertainty limit of ±20%, the mean interannual discharge (5.74 ± 1.44 m ³ s ^?1) (±SE), was found highly variable (CV: 151%; 0.8–38 m ³ s ^?1). In a normal rainfall year (2008–2009; ～1550 mm), the discharge was 5.12 ± 1.75 m ³ s ^?1, whereas in a drought year (2009–2010), it reduced by 30% with the reduction in ～23% rainfall (CV: 85%). In an excessive rainfall year (once-in-a-century event) (2010–2011; ～3050 mm), discharge as well as total solid load was ～200% higher. Monsoon months (July–September) accounted for more than 90% of the annual solid load transport. The ratio of dissolved to suspended solid (C/P ratio) was consistently low (<1) during monsoon months and higher (1–7) during the rest of the dry period. C/P ratio was inversely (R ²=0.49), but significantly (P <0.001) related to the rainfall. The average mechanical erosion rate in the three different rainfall years was 0.24, 0.19 and 1.03 mmyr ^?1, whereas the chemical erosion was estimated at 0.12, 0.11 and 0.46 mmyr ^?1, respectively. Thus, the average denudation rate of the Tons sub-watershed has been estimated at 0.33 mmyr ^?1 (excluding extreme rainfall year: 1.5 mmyr ^?1). Our results have implications to understand the hydrological behaviour of the Lesser Himalayan watersheds and will be valuable for the proposed and several upcoming small hydropower plants in the region in the context of regional ecology and natural resource management.  相似文献   

The Himalayan cryosphere: A critical assessment and evaluation of glacial melt fraction in the Bhagirathi basin     

Abul Amir Khan  Naresh Chandra Pant  Anindaya Sarkar  S.K. Tandon  Meloth Thamban  Mahalinganathan K. 《地学前缘(英文版)》2017,8(1):107-115

The cryosphere constitutes an important subset of the hydrosphere.The Himalayan cryosphere is a significant contributor to the hydrological budget of a large river system such as the Ganges.Basic data on the cryosphere in the Himalaya is inadequate and also has large uncertainties.The data on glacial melt component in the Himalayan rivers of India also shows high variability.The Gangotri glacier which constitutes nearly a fifth of the glacierized area of the Bhagirathi basin represents one of the fastest receding,large valley glaciers in the region which has been surveyed and monitored for over sixty years.The availability of measurement over a long period and relatively small glacier-fed basin for the Bhagirathi river provides suitable constraints for the measurement of the glacial melt fraction in a Himalayan river.Pre- and post-monsoon samples reveal a decreasing trend Of depletion of δ~(18)O in the river water from glacier snout(Gaumukh) to the confluence of the Bhagirathi river with the Alaknanda river near Devprayag.Calculations of existing glacial melt fraction(~ 30%at Rishikesh) are not consistent with the reported glacial thinning rates.It is contended that the choice of unsuitable end-members in the three component mixing model causes the overestimation of glacial melt component in the river discharge.Careful selection of end members provides results(~11%at Devprayag) that are consistent with the expected thinning rates.  相似文献   

Geological and mineralogical study of eclogite and glaucophane schists in the Naga Hills Ophiolite,Northeast India     

Naresh C. Ghose  Om Prakash Agrawal  Nilanjan Chatterjee 《Island Arc》2010,19(2):336-356

A variety of low‐ to high‐pressure metamorphic assemblages occur in the metabasic rocks and metachert in the Upper Cretaceous–Eocene ophiolite belt of the central part of the Naga Hills, an area in the northern sector of the Indo–Myanmar Ranges in the Indo–Eurasian collision zone. The ophiolite suite includes peridotite tectonite containing garnet lherzolite xenoliths, layered ultramafic–mafic cumulates, metabasic rocks, basaltic lava, volcaniclastics, plagiogranite, and pelagic sediments emplaced as dismembered and imbricated bodies at thrust contacts between moderately metamorphosed accretionary rocks/basement (Nimi Formation/Naga Metamorphics) and marine sediments (Disang Flysch). It is overlain by coarse clastic Paleogene sediments of ophiolite‐derived rocks (Jopi/Phokphur Formation). The metabasic rocks, including high‐grade barroisite/glaucophane‐bearing epidote eclogite and glaucophane schist, and low‐grade greenschist and prehnite–clinochlore schist, are associated with lava flows and ultramafic cumulates at the western thrust contact. Chemically, the metabasites show a low‐K tholeiitic affinity that favors derivation from a depleted mantle source as in the case of mid‐ocean ridge basalt. Thermobarometry indicates peak P–T conditions of about 20 kb and 525°C. Retrogression related to uplift is marked by replacement of barroisite and omphacite by glaucophane followed by secondary actinolite, albite, and chlorite formation. A metabasic lens with an eclogite core surrounded by successive layers of glaucophane schist and greenschist provides field evidence of retrogression and uplift. Presence of S‐C mylonite in garnet lherzolite and ‘mica fish’ in glaucophane schist indicates ductile deformation in the shear zone along which the ophiolite was emplaced.  相似文献   

The effects of chemical reactions on the dispersion of air pollutants over area sources     

Ram Naresh  R. Nath 《Earth, Moon, and Planets》1990,48(2):99-111

An analytical study has been performed to examine the characteristics of two-dimensional steady-state advective-diffusive transport of air pollutants emitted from ground-based area sources. The solutions for the concentration of air pollutants are obtained by Integral and Variational Imbedding methods taking chemical reaction process into account. A comparative study of concentration is displayed graphically, followed by a quantitative discussion.  相似文献   

Dynamic analysis of dams with nonlinear slipjoints     

Avinash C. Singhal  Milton S. Zuroff 《Soil Dynamics and Earthquake Engineering》1998,17(3):185-196

A nonlinear, slip-joint element for analyzing the effect of discontinuities on a concrete, arch dam's seismic response is developed. The joint element has been incorporated into a finite-element-based, solution for predicting dynamic structural response. This joint model, plus the numerical procedure incorporated into the incremental solution, models inter-element impact across a joint when adjacent, structural elements separate and later collide. Collision is incorporated into the incremental analysis by calculating the exchange of momentum and energy with the equations describing eccentric, rigid-body impact. Joint material's force-deflection relations are multi-linear with hysteresis. Coulomb friction is also modeled. The joint element and numerical procedure have been tested with two models. The first is a segmented arch of seven, straight beam elements connected to one another. The arch dam has been experimentally tested. Analytical results are compared with experimental results from the sealed model. Second is a rectangular plate model subject to lateral base accelerations. One horizontal edge is fixed and the opposite edge is free. The vertical edges may be fixed or connected to the base by joint elements.  相似文献   

Origin of “paired” aseismic rises: Ceará and Sierra Leone rises in the equatorial, and the Rio Grande Rise and Walvis Ridge in the South Atlantic     

Naresh Kumar   《Marine Geology》1979,30(3-4):175-191

In the equatorial Atlantic the Ceará and Sierra Leone rises lie on opposing sides of the mid-ocean ridge and are equidistant from its axis. The northern and southern boundaries respectively, of the two rises are formed by the same fracture zones. The area of shallowest acoustic basement under the Ceará Rise coincides with the presence of a 1–2 km thick seismic layer (velocity: 3.5 km/sec) lying over the oceanic layer 2. This 3.5 km/sec layer is interpreted as a sequence of volcanics which began erupting about 80 m.y. ago when the sites of the two rises lay at the ridge axis. As the “abnormal” volcanic activity ceased, the breakup of this volcanic pile into two pieces has formed the Ceará and Sierra Leone rises.

In the South Atlantic, the northern and southern boundaries of the Rio Grande Rise are also formed by fracture zones and an approximately 1 km thick layer with a velocity of 3.5 km/sec exists also under this rise. The same fracture zones appear to bound the Walvis Ridge. Drilling data suggests that both the Rio Grande Rise and Walvis Ridge have subsided continuously since their creation. The igneous rocks recovered from both rises consist of alkalic basaltic suites typical of oceanic volcanic islands. The existing data favor a model in which “excessive” volcanism along the same segment of the Mid-Atlantic Ridge created both the South Atlantic aseismic rises between 100 and 80 m.y. ago. In both the examples, the northern and southern boundaries of the rises are formed by the same fracture zones which originally bounded the abnormally active segment of the ridge axis.  相似文献   

A laboratory study of collapse behaviour of remoulded loess under controlled wetting and flooding     

Sonal Singhal  Radhey S. Sharma 《Geomechanics and Geoengineering》2016,11(2):159-163

This paper presents the effect of initial placement conditions and flooding stress (vertical compressive stress at flooding) on the collapse potential of remoulded loess. Compacted specimens of loess were tested in a one-dimensional consolidometer to study the collapse behaviour. Initial water content, dry unit weight and flooding stress were varied. Collapse potential was found to be dependent on initial water content, initial dry unit weight and flooding stress. Partial collapse was studied by allowing measured increments of water into the specimens.  相似文献   

The effects of pre-season high flows,climate, and the Three Gorges Dam on low flow at the Three Gorges Region,China     

Zhenkuan Su  Xun Sun  Naresh Devineni  Upmanu Lall  Zhenchun Hao  Xi Chen 《水文研究》2020,34(9):2088-2100

The efficient operation of a multipurpose reservoir requires information on high and low flows. However, analyses of inflows for high flows and for low flows are typically done independently. In this paper, we considered the joint dependence of the low flow on the preceding high flow volume and duration for the wet season in the Three Gorges region of the Yangtze River Basin in China. High flow volume and duration were found to have a strong association with the annual minimum 7-day flow in Cuntan, Wanxian, and Yichang stations. Furthermore, we identified the Arctic Oscillation, Pacific Decadal Oscillation, and snow cover in the Tibetan Plateau to have statistically significant teleconnections with the annual minimum 7-day flow. Bayesian models that consider a different level of pooling of the site by site regressions were then developed for the annual minimum 7-day flow conditional on the climate indices and high flow volume (or duration). The full pooling model performed best, suggesting that a homogeneous regional response is best identified given the global climate predictors. Statistics such as the deviance information criterion and reduction of error, coefficient of efficiency, and coverage rate under cross validation indicate the good performance of the model. Snow cover in the western Tibetan Plateau and high flow volume were identified as the most influential factors of the annual minimum 7-day flow through their impact on water storage in the basin. Recent simulations since June 2003, when the Three Gorges Dam operation started, were used to analyse the effect of dam operation on the annual minimum 7-day flow. A comparison of observations and predictions during the post-dam period demonstrated that the dam operation effectively modifies the annual minimum 7-day flow period to have higher flows.  相似文献   

Neoproterozoic age based on microbiotas from the Raipur Group of Baradwar sub-basin,Chhattisgarh     

Rupendra Babu  Veeru Kant Singh  Naresh Chandra Mehrotra 《Journal of the Geological Society of India》2014,84(4):442-448

An assemblage of structurally preserved organic-walled microfossils (OWMs) from the macerated residue of black carbonaceous shale belonging to Saradih Formation, the youngest carbonate horizon of the Raipur Group, Chhattisgarh Supergroup exposed at on the right bank of Mahanadi River, NE of Sarangarh township in Raigarh district, Chhattisgarh is being reported for the first time. The assemblage is comprised of 19 taxa of 13 genera belong to eukaryotes and prokaryotes viz. Leiosphaeridia, Stictosphaeridium, Dictyotidium, Synsphaeridium, Symplassosphaeridium, Satka, Trachysphaeridium, Goniosphaeridium, Trachyhystrichosphaera, Vandalosphaeridium, Siphonophycus, Oscillatoriopsis and Polythrichoides. The comprehensive account of recovered microbiotic assemblage can be correlated with globally known Neoproterozoic (early Cryogenian) assemblages, deposited in tidal complexes of shallow sea.  相似文献   

G. Vallinayagam (1961–2013)     

Naresh Kochhar  R. Baskar 《Journal of the Geological Society of India》2014,83(6):713-713

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