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GIS techniques for carrying capacity study of Damodar River Basin
Data for solid wastes generated in the year 1991 at
selected mahor towns within DRB was collected and projections made for the years
2001, 2011 and 2021 [cmr97].
The quality of life was assessed by
surveying a selected set of DRB blocks in Bihar and West Bengal by CMRI and
National Institute of Small Mines. Based on the survey data collected by these
two organisations, a subjective index and objective index were determined for
the sampled blocks. QOL indices were provided as numerical values for the
surveyed blocks [CMR97]. These values were associated attribute data with the
block map of DRB.
Micro Database Creation
He micro database contains detailed maps at
scales ranging from 3960 to 250,000 for selected areas of DRB. The region is
rich in coal deposits and mining activity is carried out in seven major coal
fields within DRB. As coal mining is an important activity in DRB, the micro
database contains maps of seven major coal fields of DRB.
- Raniganj
- Jharia
- Ramgarh
- East Bokaro
- West Bokaro
- North Kamapura
- South Kamapura
For each coal field a polygonal theme
comprising coal deposit areas, built-up areas, etc., and a linear features theme
comprising roads, lineaments, etc., have been created as themes for some of the
coal fields based on source maps from Central Mine Planning & Design
Institute Ltd.
Town maps of priority towns of DRB, namely Dhanbad,
Bokaro and Raniganj, and are also included in the micro database.
Geographic Analysis/Modelling
The goal of geographic analysis
and modelling is to find answers to physical issues related to the application:
in this study, to identify hot spots in DRB and depict scenarios for
hypothetical what-if questions. Analysis and modelling of geographic data may be
on either of the two data domains integrated by GIS systems, namely spatial or
geometric data and attribute data domains. In our discussion on geographic
analysis and modelling we exclude geographic querying [SMM94] operations
supported by GIS systems.
The effectiveness of a GIS in solving
application problems is highly dependent on the techniques used and the kind of
operations supported by the GIS package. In addition to conventional vector
overlay operations, a number of other techniques can be used for analysing and
modelling geographic data. For the CCDRB project a number of GIS techniques were
identified and used to address issues related to the basin. The following
techniques were used in this study.
- GIS theme operations
- Formula application
- Qualitative analysis
- Change detection analysis
- Socioeconomic data models
- Multi-parameter analysis
- Presentation charts
Analysis and modelling operations involve
multiple steps creating data for the next step. Due to the size of data,
operations can be time consuming.
The above techniques of geographic
analysis and modelling employed in this project are explained below briefly.
GIS theme Operations
A GIS supports a number of operations on
thematic layers for combining, extracting and transforming map data. In vector
GIS packages these operations work on both spatial and attribute data domains.
The operations are well defined geometric and topological operations which are
also given a semantics in the attribute domain [SMM94]. Due to the evolutionary
nature of GIS systems, the attribute domain semantics is somewhat ad-hoc. For
some of the theme based operations which combine thematic layers, the input
layers used for the operations must be geo-referenced. GIS theme operations are
sometimes referred to as spatial modelling or overlays [Bur86].
For
example, a map of degraded land can be generated by merging land parcels that
have a certain degree of erosion, flooding status and are salt affected. Using
extraction and transformation operations forest cover within coal fields can be
identified from data generated for the whole basin.
Formula
Application
An attribute column value in the data tables of the geographic
database may be computed by a mathematical formula using some of the other data
columns in the table. For example, the watershed wise ground water recharge can
be computed as a formula based on area value and average rainfall of a land
parcel.
Qualitative Analysis
A typical method used in GIS
modelling is to compute numerical values for each spatial feature in a theme and
classify the numerical values on an interval basis. For example, the literacy
levels of blocks may be ranked on a five point scale of values very good, good,
average, poor and very poor based on numerical values of literacy for each
block. This method converts quantitative data to qualitative data depends on the
domain knowledge of the expert choosing the intervals for quality
classification. A number of statistical techniques can be used for the
classification [Bur86].
Change Detection Analysis
An important
use of a GIS is to identify temporal changes in spatial data. The temporal
factor may be based on past, current and future scenario data in the geographic
database. For example change in forest cover over decades can be detected
subject to availability of forests cover data for decadal periods. Change
detection analysis is done using spatial modelling operations such as theme
combination, extraction and polygon aggregation.
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