KOCHI: T he water level of Periyar and other rivers, that had enacted the dance of destruction displacing over 3.5 lakh people and killing hundreds, post floods is making everyone question whether this is a precursor to another natural calamity. If the water level marker placed by the KWA on the bed of the Periyar is taken as an indicator, it is clear the river is flowing way below its former level. Besides, people are also worried about the drastic fall in water levels in wells.
According to E Shaji, assistant professor, Department of Geology, Kerala University, all rivers in Kerala flow through lineaments. “In the case of rivers, the sudden drop in water level might have been due to the seepage of water into their lineaments,” he said. Lineaments are big fractures or faults.
These fractures, he said, are the results of structural disturbances 60 million or so years ago. They might even have developed during the formation of the Western Ghats or the continental break up.“During this phenomenon, weak plains or shear zones developed. The river normally flows through such weak plains. There is a major shear zone called Achenkovil Shear Zone. This zone has some control over the flow of Achenkovil, Pamba and Manimala Rivers,” Shaji said.
The shear zone, he said, has parallel lineaments and might have opened up due to the pressure exerted by the huge volume of water released into it. “Water in the river might have escaped through this lineament,” he said. In a normal case, some amount of water remains for a particular period of time in a floodplain. “However, here, such a thing has not happened. Hence, the only primary explanation that can be made is that the lineaments have opened up and water has seeped into it. It should be noted that some of these lineaments are 10 km deep. So, the water level has to come up, then the fissure will have to reach the saturation point,” he said.
According to P K Sabu, a retired geologist, this lowering of water level in the river will indirectly affect the groundwater level. “In such a case, the river turns effluent. It draws in water from the ground level. This, in turn, leads to a drop in the groundwater table,” he said. This, he said, may be a possibility and more studies have to be done to validate the fact regarding the situation the state is facing. Sabu said, “The huge pressure exerted by the volume of water that flowed into the rivers after the dams were opened might have led to a readjustment of hydrogeological properties of the aquifer. So, we may face a potable water crisis.”
aquifer dynamics
Water seeps into the aquifers as the result of the porosity of the land surface. There are two types of porosities. One is called the primary and the other secondary. Primary porosity occurs in the upper soil layer made up of weathered materials. This laterite cap rests above a basement of crystalline rock. Secondary porosity is associated with the layer below the primary. The layer here is made up of fissures, fractures and joints. These fissures or fractures act as the conduits to the aquifer. However, all the water that accumulates on the surface doesn’t seep down into the aquifers.
Periyar conundrum
Experts say water might have escaped through Periyar lineament. Studies have to be conducted to verify if realignment of the lineaments happened in Kerala