4.4 Spatial distribution and overlay analysis
Contour plots of TDS illustrates that during premonsoon
(July 2008), wells belonging to the
1 st layer in both north and southern direction of River Noyyal shows high TDS and the entire
region is found to be affected due to the percolation of polluted water (Figure.4). It may be
noted that the fifth zone wells in the 1 st layer shows reduced values which may be due to the
location of these wells far away from the Orathapalyam dam. In the case of premonsoon
(July 2009), similar distribution pattern is observed but the contour pertaining to the TDS
value of 2000 to 2500 mg/L demonstrates a continuum from the 1 st zone to the 4 th zone in the
1 st layer reflecting that the percolation of polluted water further worsening the wells falling in
this layer. Wells belonging to the 2 nd layer illustrates lower TDS values compared to the 1 st
layer and during July’ 2008, most of the wells falls in the TDS range of 1500 to 2000 mg/L.
Spatial distribution pattern of the subsequent layers show that the water from these wells are
not much affected and many of these wells shows low TDS. Almost similar pattern of spatial
distribution is observed in the case of postmonsoon values and except the 1 st and 2 nd layer, all
other wells show very low TDS and suitable for both domestic and irrigation purposes.
Seasonal effect is found to be significant as many wells in the contours illustrating the
affected region decreases during postmonsoon due to dilution of chemical composition. The
integrated overlay of the contours belonging to the four periods was carried out and the
overlay map shows clearly that the zone 1 of layer 1 is the most affected which is found to
exist very close to the polluted water stored in the Orathapalayam dam. Zone 2 of layer 1 also indicates that the wells are highly affected but to a slight lesser degree compared to zone
1 of layer 1 wells. The overlay map shows that the wells falling in the northern part of River
Noyyal are less polluted compared to the wells in the southern part. The integrated map
clearly demonstrates that the wells belonging to the 3 rd , 4 th and 5 th layer are not polluted and
the influence of River Noyyal is not significant at these levels.