Which of the following is/are the possible consequence/s of heavy sand mining in riverbeds?

1. Decreased salinity in the river

2. Pollution of groundwater

3. Lowering of the water-table

Select the correct answer using the code given below:

The correct option is 2 and 3 only.

Let us analyze each of the points to understand the environmental impacts of heavy sand mining in riverbeds:

1. Decreased salinity in the river (Incorrect):
Excessive removal of sand from riverbeds lowers the riverbed level. In coastal regions or estuaries, this deepening allows seawater to flow further inland into the river channel. Consequently, riverbed sand mining leads to an increase in river water salinity (saline intrusion), rather than a decrease. Therefore, statement 1 is incorrect.

2. Pollution of groundwater (Correct):
Sand acts as a natural filter for water passing through the riverbed into aquifers. Excessive sand mining depletes this protective filter layer. Additionally, when the riverbed is excavated below the groundwater table, contaminants from surface runoff and agricultural activities directly enter the groundwater system, leading to groundwater pollution. Therefore, statement 2 is correct.

3. Lowering of the water-table (Correct):
Sand holds water like a sponge and supports the hydraulic connection between the river stream and adjacent underground aquifers. When large volumes of sand are mined, the river bed is deepened (incised), which drains groundwater from the surrounding alluvial aquifer into the deeper riverbed channel. This causes a significant lowering of the surrounding water table. Therefore, statement 3 is correct.

Hence, statements 2 and 3 represent the actual consequences of heavy sand mining in riverbeds.