Rivers, the lifelines of the land

RIVERS have always been important to humans, and many of the world’s ancient and greatest civilisations were established near rivers. Even today, the capitals of several countries are situated on riverbanks.

Rivers benefit communities in ways that are easily recognisable: they are a source of water for domestic, agricultural and industrial purposes and of food and livelihoods; they can be used for transportation; those that are amenable to damming are used to supply energy needs; and they are often used for recreational and religious activities. Rivers also serve less obvious functions that are as important as the obvious ones. They are feeding and spawning areas for fish and other aquatic biota and can purify water as they have the ability to break down or absorb pollutants. A properly maintained river system can act as a drainage area and help in flood management. Because the water table is at or close to the surface in river basins and because sand retains water, rivers perform the important functions of water storage and groundwater replenishment. The last two functions are applicable to dry rivers as well as those with perennial flows.

A river ecosystem is the sum of the water, animals, plants, microorganisms and organic and inorganic material—such as sand, gravel and rock—it comprises and their interactions. Although fish are readily associated with rivers, it is insects that form the major part of a river’s animal life. What makes this ecosystem different from other wetland systems is that there is a unidirectional flow of water and that its flora and fauna are adapted to this trait. The rate of flow is not a constant, varying at different points along the course and with seasons. Heavy precipitation can cause a sudden increase in flow. The chemistry of river water and what organic and inorganic matter it contains depends on what it picks up from its catchment area and along its flow path. Pollution, usually because of human activities, has a huge impact on water chemistry. Oxygen is the crucial chemical constituent of rivers, the concentration of which determines a river’s ability to sustain life and cleanse its waters.

Unscientific sand mining depletes the mineral at rates at which the river system cannot replenish it. This is particularly so in the case of rivers that are dry for most of the year. Excessive mining undermines the ability of riverbeds and riverbanks to support the infrastructure built on them, such as bridges, electricity poles and buildings, because it weakens the structural integrity of the sand. It leads to the loss of groundwater and a diminishing of the river’s capacity for groundwater recharge. This can increase the salinity of groundwater and lead to saltwater intrusion into the aquifer.

Over time, any river ecosystem will change through the natural processes of erosion and sedimentation, but sand mining makes changes in an unsustainable and indiscriminate manner and irreparably damages the ecosystem.

Sashikala Asirvatham