Deforestation, sand mining bring water table downPublished by MAC on 2005-09-05
Deforestation, sand mining bring water table down
G.K. Nair The Hindu Businessline, Kochi (Kerala)
5 September 2005
According to a study, water availability by 2050 in the rivers Achankovil, Pampa and Manimala will drop by 459 million cubic metres, 3,537 million cubic metres and 398 million cubic metres respectively.
The sharp fall in the underground water table in the river basins in Kerala after the rains, a recent phenomenon, is said to be the outcome of deforestation and indiscriminate sand mining resulting in the deepening of riverbeds.
The river sand bed used to act as natural check dam because of the voids of 45 to 50 per cent in the soil where the water is retained, environmental activists told Business Line.
"This phenomenon maintains the ground water level in all the catchment areas and the river basin."
When the riverbed level falls, the hydraulic gradient increases, leading to higher velocity. As a result, immediately after the monsoon, the water flow into the rivers is drained out quickly.
Unlike in the past, rivers are filled during the rains but after a few days of dry weather they become skeleton, said Mr N.K. Sukumaran Nair, General Secretary of the NGO, Pampa Parirakshana Samithi.
"In the absence of sand, no natural retention of water takes place. Sediment deficient flow of `hungry water' picks up more sediment from the stream below the mining site, furthering the degradation," he said.
The normal monsoon season in Kerala is from June 1 to November 30 and the State used to receive on an average 3,000 mm of rainfall. Until a decade ago, the water table used to remain at higher levels up to March. But the situation has totally changed now immediately after the southwest monsoon. The water level in the rivers has fallen drastically, leading to drought conditions. The wells in the river basin and the catchment areas are also drying up fast following the drop in the underground water table, said Mr Nair.
Environmental degradation is pointed out as the reason for such a dangerous situation. According to a study by the Kozhikode-based Central Water Research Establishment, water availability by 2050 in the rivers Achankovil, Pampa and Manimala will drop by 459 million cubic metres, 3,537 million cubic metres and 398 million cubic metres respectively.
Sand mining, coupled with destruction of forests in the State, is said to have adversely affected the river system, he said.
The soil in the forest area used to retain 40 to 50 per cent of the rainwater and then slowly it is percolated down. Thereafter, it seeps into small streams and then flows into the rivers. Now, large-scale deforestation by encroachers and activities under the disguise of development have reduced the tropical forest area significantly, environmentalists point out.
The underground water table in the catchment areas and the river basins is related to the surface water level in rivers. Indiscriminate sand mining during the past two decades has deepened the riverbed by an average three to four metres, while there are points where it has dropped by six metres. Consequently, the water table in the wells in the catchment areas and the river basins have also fallen sharply to the surface water levels in the rivers.
Added to this is the reclamation of paddy fields and other marshlands, which used to function as natural reservoirs where the rainwater is accumulated. This phenomenon too contributes to maintaining the underground water table at higher levels for longer periods. In such areas too, there is now water scarcity.
Another significant factor contributing negatively to rainwater conservation is the removal of soil from the bushy hilly terrains for filling low-lying areas such as paddy fields and marshlands for construction activities.
If these activities are not controlled and regulated by the authorities, the water scarcity in the State will become serious in the years to come, albeit it is already acute in the mid and high lands in several districts, the environmentalists warned.