It is as if Kunthipuzha in Palakkad, like a honeybee that falls dead after stinging, has ceased to exist after giving full vent to its fury during the floods. The river bed is almost dry and, like in some post-apocalyptic world, is now buried under giant white pebbles. Weirder still, nearly 2km of its banks at Thattengalam resemble a beach after the floods had washed up vast deposits of silt and fine sand; a dead river with a beach.
Perhaps in this 'beach and giant pebble' phenomenon lies the key to understanding the falling water levels in rivers and wells in the state's midlands. “The high velocity August rains like a powerful underwater dredger has forced out the silt and fine sand that forms the surface of the river bed,” said Nizamuddin A, the land use board commissioner. It is this flood-removed fine sand that has formed the beach along the Thattengalam area near Mannarkkad in Palakkad.
Drop and pull effect
The silt and fine sand play a crucial role in maintaining the river water level. Most of the rivers in the midlands, right from Periyar and Pamba to Vamanapuram river in Thiruvanathapuram, have gone more than half dry. When the river level dropped, the hydrologic gradient (the difference between the groundwater level in nearby wells and the river water level) turned steep. Result: water in wells and ponds drained down into the river, as if pulled down. “This is why water level in the wells surrounding rivers have gone down after the floods,” Nizamuddin said. The land use board's inference is based on a preliminary study of Kunthipuzha, which is now on.
Another preliminary study being conducted by the Centre for Water Resources Development and Management has complimented the land use board study. The CWRDM study has found that the sand bed over one metre thick of Punoor Puzha in Kozhikode has been eroded away by the flood. There, too, the water level has fallen, and nearby wells too have shown a dramatic fall in water level.
Pebble accumulation
Along with the erosion of the sand bed, the rampaging floods also deposited soil and stones and rocks on the river. This virtually prevented the rain water from percolating down, as is usual during normal rainfall. There was another reason why not much water sank down during the recent floods. “The rivers flowed with such speed that they destroyed the check dams and all kinds of hurdles that were erected to dam its flow. The result was, the water just rushed along the east-west slope without collecting anywhere,” Nizamuddin said.
Sustained dry spell
Still, none of this - the removal of the sand bed or pebble deposition or fall in water level - would not have been a problem had it rained after the floods. Between August 22 and September 12, the state had received just 41.7mm of rainfall. “This is something that will evaporate in 10 days,” said Dinesan P V, head scientist of CWRDM's geomatics division. Even during the drought year of 2016, the state had received 64.6mm of rainfall during the corresponding period.
“All our rivers are rain-fed and so we need rain to replenish our rivers,” Dinesan said. The CWRDM was at the moment studying flood-induced hydrological and topographical alterations in rivers in Kozhikode. “Once this study is complete, we might go for a pan-Kerala study,” he said.
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