Multi criiteria analysis using GIS for ground water resource evaluation in Rawasen and Pili Watershed, U.P.
Methodology
The
groundwater exploration in the study area involved thematic map generation and
their integration through GIS. Geology, Landuse, Geomorphology and Lineament
maps were derived from interpretation of Satellite Images and Aerial Photographs
supported by selective ground truth verification. Drainage map was prepared
using Survey of India toposheet on 1:50,000 scale. Slope map was obtained by
creating DEM after interpolation of spot height and contour in GIS. For
integration all the maps were converted into digital format in the GIS. Prior to
integration of different information, individual class weights and map scores
were assessed based on Satty’s Analytic Hierarchy Process. In this method
a pairwise comparison matrix was prepared for each map using Satty’s nine
point importance scale and this matrix was solved using Eigon Vector method. In
this method the basic input is the pair wise comparison matrix "A" of
order nxn constructed based on Satty’s scaling ratios.
A = [ aij ] where i,j = 1,2,3
….n
The matrix "A" has generally the
property of reciprocity and also the consistency. This is explained as
Aij = 1/aji
Mathematically the equation of matrix can be
defined as
(A - Il ) x = 0
I = Identity matrix of order of n x
n
l = Eigon value
x = Eigon vector
This resulted in individual
class weights. The map scores were also calculated by same method. These weights
were multiplied with map scores and applied to linear summation equation
(proposed by Voogd 1983)
S = S wi xi
S =
weighted map
wi = weight of individual class
xi = map scores
This resulted in a unified weight map
containing due weights of all input variables. The weight values ranged from
1.58 to 29.072. This map was further logically classified to arrive at
groundwater potential zone map.
Results & Discussions
The main factors responsible for groundwater resource development are
geology, geomorphology, landuse/landcover, slope, lineaments etc. Geologically
the area is characterised by distinct rock types showing structural and
stratigraphic controls. These rocks are quartzites, phyllites and schists of
Garhwal and Tal group, red shales of Subathus, sandstone and shales of Siwaliks
and Recent Alluviums. Alluviums, middle and Upper Siwalik sandstone and Garhwal
quartzites are supporting good groundwater regime (Fig. 1). Geomorphology is one
of the main controlling factor of groundwater. Genetically the landforms of the
study area were divided in three parts i.e. Fluvial origin, Denudational origin
and Structural origin (Fig. 2). The landforms such as flood plain, alluvial fan,
fan terrace are supporting good groundwater condition. The landuse refers to the
main activities and human intervention and are carried on land. Two level of
classification was done in area by visual interpretation of satellite data of
two seasons i.e. April and November (Fig. 3). The maximum area was occupied by
dense forest followed by agricultural land.
Slope map is generated from the contours and
spot heights taken from the SOI toposheet consist of five classes from gentle to
very steep slope (Fig. 4). Gentle, moderately gentle and moderate slopes are
supporting favourable conditions.
The drainage system of an area gives important
clues of the subsurface conditions, which helps in deciphering groundwater
conditions of that area. The common drainage patterns observed in the study area
are parallel to sub-parallel and dendritic. Parallel to sub-parallel pattern is
dominant in siwalik group of rocks, whereas in garhwal group of rocks mainly
dendritic to sub-dendritic pattern is found (Fig. 5). Water divide zones were
delineated with the help of drainage map because they are the zones where no
percolation of water takes place and are not suitable for groundwater storage
(Fig. 6).
Lineament plays vital role in the development
of groundwater regime. Lineaments were mapped from aerial photographs and
satellite images. IRS LISS III-B AND 3 digital data is also used to delineate
the lineaments by applying – 5 x 5 predefined directional filter. Which
has enhanced the edge and helped in updating the lineament map. These lineaments
were classified in four classes i.e. major, minor, fault and thrust depending
upon their nature and extent. Fault and thrust were not considered in the study
because of non-availability of any ground data to assess their behaviour. Major
and minor lineaments were considered in study and buffer zones of 75m and 150m
for major and 50 m and 100 m for minor lineaments are taken for study (Fig.
7).