One of the major victims of these activities is the River Pampa. Sand mining has removed the sand bed exposing the clay soil in several parts.

Kochi May 28 Ever increasing human intervention in several major rivers in Kerala in recent years has changed their physical structure in such a way that it might sound the death knell of these rivers, if the authorities continued to be indifferent.

Indiscriminate sand mining, check dams across the rivers and separating large part of the sand bed as an enclosure for other purposes by dividing the river using permanent construction and so on, have been pointed out as the reasons for the degradation of the rivers.

One of the major victims of these activities is the River Pampa. Sand mining has removed the sand bed, which used to remain as a carpet, exposing the clay soil in several parts.

As a consequence, thickets have been formed in the river at many places and it shows that the river degradation has reached its acme, Dr Thomas P. Thomas of the Botany Department, St Thomas College, Kozhencherry, an agriculturist and environmental activist told Business Line.

Thickets in the middle of the rivers have become grazing ground for the cattle and that in turn help the accelerated growth of the shrubs and grass etc.

Eventually, the River Pampa has become a narrow stream at many points.

Sand mining has pushed down the underground water table, which has not only created drinking water shortage but also has negatively affected several crops in the river basin, he said.

"In fact, the agricultural pattern has changed," he pointed out.

The whole 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, a water technologist said. "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 flows 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, an Engineer and 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 process," he claimed. Thickets have come up at many points in Bharathapuzha and Periyar rivers also, he said. 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 fell drastically leading to drought conditions. The wells in the river basin and the catchment areas dry up fast following the drop in underground water table, he pointed out.

Environmental degradation is pointed out as the reason for such a dangerous situation. According to a study of the Kozhikode-based Central Water Research, the water availability by 2050 in the rivers Achankovil, Pampa and Manimala would drop by 459 million cubic metres, 3,537 million cubic metres and 398 cubic metres, respectively.

Sand mining, check dams upstream and blocking normal water flow by dividing the river and destruction of forests in the State 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 is seeped into small streams and then flows into the rivers. Now large-scale deforestation by encroachers has reduced the tropical forest area significantly, another environmentalist pointed out.

Indiscriminate sand mining during the past two decades had deepened the riverbed by an average three to four metres while there are points where it had dropped by six metres. Consequently, the water table in the wells in the catchment areas and in the river basins also fell sharply to the surface water levels in the rivers.

If all these activities were not controlled and regulated by the authorities the water scarcity in the State would acquire serious dimensions in the years to come albeit it is already experienced in mid and high lands in several districts of the State, they warned.