Previous Year Question

River sand is not merely a construction material; it plays an important role in maintaining river structure, groundwater recharge, natural filtration of water and aquatic habitats.

Excessive sand mining lowers the riverbed and may alter the natural shape and flow regime of the river.

Statement 1 is incorrect: A decrease in water salinity is not a general consequence of heavy sand mining.

In coastal and tidal river regions, deepening of the riverbed may allow saline seawater to penetrate farther into the river and adjoining groundwater.

Therefore, in some regions, sand mining may cause saline-water intrusion and increased salinity instead of decreasing salinity.

Statement 2 is correct: Sand present in a riverbed acts as a natural filter for water.

Removal of the sand layer may reduce the natural filtration capacity and make it easier for pollutants to move from the river into adjoining aquifers.

Saline-water intrusion in coastal regions may also deteriorate groundwater quality and make it unsuitable for drinking or irrigation.

Silt generated by mining, oil leaking from machinery and other local pollutants may also affect surface water and groundwater.

Statement 3 is correct: Lowering of the riverbed changes the hydraulic gradient between the river and adjoining groundwater.

Consequently, water from surrounding aquifers may flow towards the river, causing the groundwater table to fall.

A falling water table may reduce the quantity of water available in wells, tube wells and wetlands located near the river.

Excessive sand mining may also cause riverbank erosion, instability of bridge foundations, the formation of deep pits in the riverbed and destruction of aquatic habitats.

Removal of sand may affect fish-breeding grounds, bottom-dwelling organisms and riparian vegetation.

Therefore, pollution of groundwater and lowering of the water table are possible consequences of heavy sand mining. Hence, only statements 2 and 3 are correct.