Correct Option (b)
Heavy sand mining in riverbeds has significant environmental consequences.
- Statement 2: Sand and gravel layers in riverbeds act as natural filtration systems. Their removal exposes underlying aquifers to surface pollutants, leading to groundwater contamination from sources such as agricultural runoff, industrial discharge, and domestic waste.
- Statement 3: Riverbed sediments, including sand, are crucial for groundwater recharge as they facilitate the slow percolation of water into aquifers. Extensive sand mining disrupts this natural process, reducing the capacity of the riverbed to retain water and replenish groundwater reserves. This often results in a lowering of the water table.
Incorrect Options
- Statement 1: Heavy sand mining, especially in coastal or estuarine river sections, can lead to increased salinity. The removal of riverbed sediments can deepen the channel and alter the hydrological gradient, facilitating the intrusion of saltwater from the sea into freshwater river systems and adjacent aquifers. Therefore, a decrease in salinity is not a typical consequence; rather, an increase is observed.
- Options (a), (c), and (d) are incorrect because they include Statement 1, which inaccurately describes a consequence of heavy sand mining. Option (a) only includes Statement 1. Option (c) includes Statements 1 and 3. Option (d) includes all three statements. Since Statement 1 is incorrect, these options are invalid. Option (b) correctly identifies the valid consequences mentioned in Statements 2 and 3.