THE BLIND-ZONE PROBLEM IN MULTIPLE REFRACTION-LAYER OVERBURDEN SITUATIONS*

The blind zone problem is examined with a view to provide a simple means of solving the problem in the general case of arbitrary number of refraction layers constituting the overburden to the masked layers. Considering the first arrival refraction interval corresponding to the masked layer which reduces to zero under blind zone conditions, a method to solve the problem is presented. Derivation of the critical distance expression is also included and convenient solutions to compute the thicknesses of the blind zone and its immediate overlayer are worked out. Based on test calculations on some known instances, the efficacy of the method is illustrated. A Fortran program for use when large numbers of refraction layers are involved under the overburden or when more than one masked layer is encountered is available from the authors.     

Analytical solution of advection–diffusion equation in heterogeneous infinite medium using Green’s function method

Some analytical solutions of one-dimensional advection–diffusion equation (ADE) with variable dispersion coefficient and velocity are obtained using Green’s function method (GFM). The variability attributes to the heterogeneity of hydro-geological media like river bed or aquifer in more general ways than that in the previous works. Dispersion coefficient is considered temporally dependent, while velocity is considered spatially and temporally dependent. The spatial dependence is considered to be linear and temporal dependence is considered to be of linear, exponential and asymptotic. The spatio-temporal dependence of velocity is considered in three ways. Results of previous works are also derived validating the results of the present work. To use GFM, a moving coordinate transformation is developed through which this ADE is reduced into a form, whose analytical solution is already known. Analytical solutions are obtained for the pollutant’s mass dispersion from an instantaneous point source as well as from a continuous point source in a heterogeneous medium. The effect of such dependence on the mass transport is explained through the illustrations of the analytical solutions.     

Near shore waves,long-shore currents and sediment transport along micro-tidal beaches,central west coast of India

Coastlines are undergoing constant geomorphologic changes with respect to the incident wave climate.Based on waves measured at 9 m water depth,simulation of near shore wave transformation is done using REFDIF-1numerical model and the near shore breaker parameters are estimated at two micro-tidal beaches along central west coast of India.Model results are validated with measured values.From the breaker parameters,long-shore current and long-shore sediment transport rates（LSTR） are computed by using semi-empirical equations.Estimated long-shore current and LSTR are showing dramatic variations with respect to seasons.Predominant direction of LSTR is observed towards north since the approach waves are from south-west direction during pre-monsoon and post monsoon.During monsoon season,waves are from west south-west and resulted in southerly transport.The estimated annual net and gross LSTR by Cambridge Environmental Research Consultants（CERC） at two locations are in the same order whereas LSTR estimated by Walton ＆ Bruno and Kamphuis equations are showing different estimations because of difference in surf-zone width and foreshore slope between the two locations.For micro-tidal beaches with length less than 6 km,Kamphuis equation is giving agreeable estimation of LSTR.Sensitivity analysis of LSTR estimate shows that coastal inclination is the prominent factor in determining LSTR than incident wave angle.     

Numerical study of mechanism of fold formation in a laminated rock

A set of large deformation experiments are presented to simulate folding pattern at various energy states during formation. In order to numerically simulate this phenomenon, a rectangular layer of shale is generated and compressed at various strain rates. The results reveal the variation in distribution of stress along the length of the bed. The stress distribution during elastic behaviour of shale bed at low compression rate and the change in stress distribution leading to rupture at high compression rates is discussed. Wavelength, limb length, bulk shortening, stress distribution, displacement of particles along the length of the bed is considered for comparative study of the fold pattern generated at various compression rates. The nature and position of crack generated during the formation of fold is also explained. After rupture in shale bed, the generation of fault and stress distribution in limbs of fold sliding over one another is also described.     

Plant studies in Himachal Pradesh,Western Himalaya: a systematic review

Owing to a predicted rise in temperature, increase in precipitation and the escalating anthropogenic stresses, the Himalayan ecosystems are the most threatened non-polar regions of the world. In the past, there have been racing extinctions and range shifts of several life forms in this region, particularly of the plant species. Therefore, consistent qualitative and quantitative records on botanical baseline data on a regular basis are indispensable. The current communication attempts to provide a detailed account on the current state of knowledge and research gaps in floristic studies of Himachal Pradesh, Western Himalaya. Based on an extensive review of more than 140 studies in the form of scientific peer reviewed literature on floristics, medicinal and aromatic plants(MAPs), rare, endangered, threatened and endemic species and ethno-botany, it is revealed that the number of floristic studies in Himachal Pradesh have surged in the past years but studies pertaining to the lower plants remain meagre. Unfortunately, the remote valleys including micro-watersheds lying in the coldarid regions are relatively less studied in terms of available growing stock and population status of MAPs. Depleting traditional ethno-botanical knowledge has been the major concern and, many threatened MAPs need to be accessed globally following IUCN standards. Thus, documentation of the conservation status of key MAPs, setting aside conservation areas around viable populations of threatened species, developing germplasm banks of the priority MAPs and monitoring the impacts of climate change has been suggested.     

Eurasian snow cover and seasonal forecast of Indian summer monsoon rainfall

Abstract

This paper presents the relationship between Indian summer monsoon total rainfall and two parameters from Eurasian snow cover, one being the winter snow cover extent and the other the area of spring snowmelt. Satellite-derived Eurasian snow cover extent and Indian monsoon rainfall data were obtained from the NOAA/NESDIS and the India Meteorological Department (IMD) for the period 1966–1985. Seasonal cyclic variations of snow cover showed a higher swing in both the winter and the spring seasons of the cycle as compared to the remaining seasons of the year in the lower region of the cycle. The established inverse relation between winter snow cover and monsoon rainfall during June to September is further extended. Winter snow cover is very strongly correlated with spring snowmelt over Eurasia. Spring snowmelt area is obtained by subtracting the May snow cover extent from that of the previous February. The variations of spring snowmelt were also compared with Indian total monsoon rainfall. The detected correlation is stronger between snowmelt and monsoon rainfall than between the winter snow cover and the monsoon rainfall. There is also a significant multiple correlation among winter snow cover, spring snowmelt and monsoon rainfall. Lastly, a significant multiple correlation suggested a multiple regression equation which might improve the climatic prediction of monsoon rainfall over India.