4.2 Wilcox diagram
Wilcox (1948) used % sodium and specific conductance in evaluating the suitability of
groundwater to irrigation. Percentage Sodium is determined from the ratio of sodium to the
total cations, namely, sodium, potassium, calcium and magnesium. Percent sodium is
calculated as follows:
%Na = 100*Na/(Na+K+Ca+Mg)
The classification of groundwater samples from the study area with respect to percent sodium
and EC are shown in Figure.2. Results show that the wells belonging to the 1 st layer, that is,
500 m away from the River Noyyal is found to fall in the unsuitable and doubtful to
unsuitable region which clearly indicate that these wells are not suitable for irrigation. In the
case of 2 nd layer wells (about 1000 m away from River Noyyal), it is observed that except one
well, all other wells are found to fall in the permissible to doubtful and doubtful to unsuitable
region indicating that most of the wells in this region also not fully suitable for irrigation.
Wells belonging to 3rd layer (about 1500 m away from River Noyyal) demonstrate that 40%
of the wells are found to be good for irrigation and the remaining 60% fall in the region of
permissible to doubtful. In the case of wells belonging to 4 th and 5th layers, most of them fall
in the very good to good and good to permissible region indicating that these wells are very
much suitable for irrigation. The results of the present study clearly demonstrate that the
influence of polluted riverwater to the groundwater aquifers is highly significant only within
1 km from River Noyyal on both north and south directions.