April, 2013

April, 2013   ||  Volume 17 No.2



HAdvection diffusion equation models in near-surface geophysical and environmental sciences

R.N. Singh

CSIR-National Geophysical Research Institute, Hyderabad 500 007

Basic near-surface geological and environmental processes such as groundwater flow, contaminants transport in aquifers, heat transport, air pollution etc. concern transport of mass in the near-surface and environmental media. Mathematical models are constructed using conservation laws such as mass/heat conservation and supplemented by constitutive relations such as Fick’s laws for concentration distribution and Fourier law for heat conduction. Combing both equations, an advection-diffusion equation is formulated for constructing the spatio-temporal distribution of the mass and heat fields in air, water and subsurface environments. We present first derivation of advection-diffusion model equation and necessary initial and boundary conditions for a well-posed problem and summarize methods which are used to construct solutions. We then present few examples of such models for solute transport in the groundwater, flow in sloping aquifer, thermal distribution in subsurface for use inferring climatic signals from borehole geothermal data, steady and transient air quality and river water quality distributions. Environmental forensics requires to find the sources of pollution from observations. This is typical inverse problem, non well-posed problem, and can be solved by least squares theory. Lastly a brief discussion is presented about fractional advection diffusion theory which is now being used to understand anomalous dispersion of pollutants in the environment.


Gravity anomalies of two-dimensional bodies

D. Bhaskara Rao

Professor of Geophysics (Retd.), Andhra University
Visakhapatanam-530 003, India.
E.mail : dbr_49@yahoo.co.in

Two simple and interesting rules are derived by extending the line integral method to find the equations for the gravitational attraction components due to a planar surface in the directions perpendicular and parallel to the surface itself. The attraction components, GAB^ and GAB||, perpendicular and parallel to the surface AB are given by GAB^ = 2 g s R (ØB – ØA) and GAB|| = 2 g s R ln (rA / rB), where R is the perpendicular distance from a point of calculation to the face AB, rA and rB are the lengths of the radius vectors of A and B, ØA and ØB are the angles made by them with X-axis. These rules are found to be useful to derive the vertical and horizontal components of gravitational attractions of two dimensional bodies bounded by planar surfaces and their applicability is demonstrated by deriving the equations for gravity anomalies of finite inclined dike and trapezoidal prism. The correctness of the anomaly equations are verified by calculating and comparing the anomalies of dike and trapezoidal models with corresponding polygon models. The stability of inversion with these models and also with polygon models are studied by carrying out inversion of synthetic and field gravity anomalies.


Studies on textural characteristics of sediments from Gosthani River Estuary - Bheemunipatnam, A.P., East Coast of India
B. Ganesh, A.G.S.S. Naidu, M. Jagannadha Rao, T. Karuna Karudu and P. Avatharam
Delta Studies Institute, Andhra University, Visakhapatnam - 530 017
Email: ganesh.mgeo@gmail.com

Detailed textural and clay mineralogical study of Gosthani estuary (lat. 17° 53’- 17°56’ N: long. 83° 26’- 83° 28’ E) has been carried out. The textural studies clearly establish that the sediments are of medium grain size, moderately sorted, positively skewed and deposited under moderate to low energy conditions with dominant rolling and suspension mechanisms. The observations are supported by the frequency curves, CM plot and bivariate plots between parameters, confirming the unimodal nature of sediments with dominant medium sand fraction mixed with minor amounts of silt and clay. The clay mineralogy of these sediments indicates that the most common mineral observed in all samples is illite. The other minerals namely kaolinite, montmorillonite and chlorite are occurring in minor amounts. The clay minerals are believed to be derived from the hinterland lithology composed of khondalites with associated acidic and basic rocks.  

Urban flooding in recent decades in four mega cities of India
U.S. De**, G. P. Singh* and D. M. Rase*
**Visiting faculty Department of Environment Science/ V.S.I. Pune, India and
Former Additional Director General of Meteorology (Research), Pune
*India Meteorological Department, Pune – 411005
E-mail: gauravendra.singh@gmail.com

Floods, extreme weather events, have occurred with frequent regularity over last two decades causing severe urban flood related inundations. In the present scenario, rapidly expanding mega cities (due to migration of people from rural India) are facing many problems. The four mega cities: Delhi, Kolkata, Mumbai and Chennai are the most populated cities of India. Uncontrolled growth of mega cities has increased their vulnerability to flooding. For a better understanding of the problem, extreme rainfall events have been analysed for the period 1970-2006 for two stations each in the four Mega Cities. Their spatial variation, frequency and trends have been computed and discussed.
In this study, analysis has been made about the casualties due to floods in these cities from the period 1988 to 2007. Data from Disastrous Weather Events published by India Meteorological Department have been used. The study brings out the impact of urban flooding, leading to human deaths, for each city taking in to context the different geographical and climatic aspects. Some measures are suggested to minimize the losses from such natural hazards.

Filtering of gravity and magnetic anomalies using the finite element approach (fea)
T. Ndougsa-Mbarga, M. Bikoro-Bi-Alou1,2, T.C. Tabod1 and K. Kant-Sharma3
*Department of Physics, Advanced Teacher’s Training College, University of Yaoundé 1,
P.O. Box 47 Yaoundé, Cameroon.
1Department of Physics, Faculty of Science, University of Yaoundé 1, P.O. Box 812, Yaoundé, Cameroon.
2 Department of Renewable Energy, Higher Institute of the Sahel, University of Maroua,
P.O. Box 46 Maroua, Cameroon.
3School of Earth and Atmospheric Sciences, Department of Applied Geology, Guindy Campus,
University of Madras, Chennai - 600 025, India.
E-mail: theopndougsa@gmail.com/tndougsa@yahoo.fr

The separation of both the Bouguer and the total magnetic field anomaly into regional and residual anomalies is one of the most important and crucial steps in the processing of Bouguer gravity and aeromagnetic data. This paper develops an approach based on the concept of shape functions used in finite element approximation. As for the application, we have written a computer code with the MATLAB software using the eight nodes grid rectangle. We have chosen to calculate the regional anomaly of the Mykawa region of Texas (USA) from published data to test the validity of our code. We have also carried out gravity investigations over the Yagoua sedimentary region located in the Far North of Cameroon, and an aeromagnetic investigation over the Ebolowa-Djoum region located in the south of Cameroon. The qualitative analysis of regional and residual gravity maps revealed respectively: (1) a non homogeneous basement and (2) the observed gravity lows as due to the sedimentary infill, and the relative gravity highs associated to structural highs or the presence of either metamorphic or volcanic rocks. Based on the magnetic study, we have subdivided Ebolowa-Djoum area in to five subzones with different particular magnetic responses. Some responses reveal a more or less important signature of iron ore deposits, while others highlight the region’s fault network.

Basin and sub-basin crustal structure of a part of the western offshore, India
R. Bhattacharyya1 and T. J. Majumdar2*
1Centre of Excellence for Energy Studies, Oil India Limited, Guwahati – 781 022, India
2Space Applications Centre (ISRO), Ahmedabad – 380 015, India
*Corresponding Author (e-mail: timajumdar@rediffmail.com)

The basin modeling/analyses based upon structure, isopach (sediment thickness), lithofacies, paleogeologic and the geophysical maps, of a part of the western offshore has been attempted. In this study, two gravity profiles have been utilized for modeling. Other geophysical information like seismic data, as obtained from ONGC and NIO published reports, and the corresponding sub-basin crustal models have been utilized for correlation and generation of whole crustal models. RE-11 has been taken as per the existing NIO model and the results of the forward model have been compared/validated with the satellite gravity data.

Geophysical investigations for solving seepage problems
Central Water & Power Research Station, Kdk, Pune-24
E-mail: ram9755@gmail.com

In many seepage problems, the streaming potential resulting from active water flow through hydraulic conduits are readily detectable by self potential method and hence this geophysical technique is commonly used to investigate dam seepages. However in the absence of fluid flow through the conduits, other geophysical methods can be used to locate seepage pathways.
This paper discusses three studies of geophysical investigations at various project sites highlighting successful utilization of other geophysical methods to identify seepage zones so that suitable remedial measures could be adopted to ensure the stability of the structure


-An Opinion

Shale gas as an energy resource- Pros and cons
P.R. Reddy
Scientist G (Retd), NGRI, Hyderabad-500 007
Email: parvatarreddy@gmail.com

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