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The process of mathematical modelling is comp 
osed of five steps viz. (i) formulation (ii) approximation/ 
transformation (iii) computation (iv) applications and (v) 
evaluation. 
Formulation refers to generation or selection of 
basic equation/algorithms governing the flow of ground 
water in the system with the domain specification and 
boundary conditions. Approximation relates to the 
selection of numerical method which can be used to 
solve the equations like finite difference, finite element 
and integrated finite difference, the equations normally 
used in ground water modelling. 
The complex step involved is computation which 
refers to the process of obtaining a solution to a large 
number of differential equations by way of using digital 
techniques with coding method. 
The application involves calibration or history 
matching of the observed and simulated heads, 
sensitivity analysis and prediction. Sensitivity tests are 
required to obtain how the model behaves in various 
extreme environments. 
The final step is evaluation of the model in the 
field condition. The results obtained in the field in 
different environments are to be evaluated by applying 
the model to arrive at the accuracy. 
Role of Remote Sensing and GIS in Ground Water 
Modelling 
At present traditional methods i.e. field mapping, 
surveying, soil profile analysis, pump test, yield 
estimation etc. are used to derive realistic parameter 
ization of the distributed heterogeneity. However, these 
methods have obvious deficiencies. They provide 
detailed “on point” information; but the regionalization 
of such point information and measurements describing 
their representativeness is still a question mark. 
By introducing the temporal analysis, potential of 
high resolution, sun synchronous earth observation 
satellite data with the powerful spatial analysis available 
from a Geographic Information System (GIS), it is 
possible to achieve Vegetation-Soil-Topography 
interface which is in turn related to landform charac 
teristics. This type of integration of Earth Observation 
data and GIS will overcome the present deficiencies to a 
greater extent and will provide a toolset for improved 
watershed or catchment model parameterization. 
Improper land and water management leads to 
environmental problems especially in the field of 
agriculture and forestry which are primarily related to 
the hydrological transport dynamics of stream 
catchments; management of water resources for a given 
watershed or river basin. Such environmental problems, 
can be differentiated into floods, land degradation and 
water pollution. They can only be dealt with through an 
integrated system approach consisting of Remote 
Sensing, GIS, processing and modelling techniques. 
Hydrogeomorphology plays an important role in 
ground water modelling especially on the data derived 
from remote sensing techniques. The following method 
will be useful in inputting the information for ground 
water modelling. 
CLASSIFICATION 
The physiographic properties on watershed basis 
can be improved with multitemporal, multi spectral and 
multi resolution data for maximum classification 
accuracy. 
IDENTIFICATION AND DELINEATION 
By means of GIS overlay analysis of geology, 
geomorphology, structure, physiography, climate, slope, 
drainage, soils and land use information, the hydro- 
logical response units, erosion response units can be 
identified. Further the grid cell analysis within GIS will 
reveal a detailed insight as connectivity, surface and 
ground water potential on intra and inter watershed 
basis. 
Parameterizing 
The utility of any model depends on the end user 
requirement, the social factors and economic parameters 
and variables by means of GIS analysis using attribute 
tables within the GIS data base. 
Validation 
The acceptability of the model depends on the 
accuracy with respect to reality and cost benefit factors. 
The parameterization by cost benefit analysis in terms of 
number of area depending on the activity and validation 
of parameters against both field data and empirical 
methods. 
It is to remember that use of remote sensing 
techniques can not serve as ‘stand alone’ method but it 
is definitely a powerful toolset and integrated to those 
already existing in water resources modelling, develop 
ment and management.