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:

Let's analyze the possible consequences of heavy sand mining in riverbeds:

1. Decreased salinity in the river: This statement is incorrect. Heavy sand mining does not generally decrease salinity in the river. In fact, if mining occurs near coastal areas or estuaries, it can lead to saltwater intrusion into freshwater aquifers and rivers, potentially increasing salinity in some stretches, not decreasing it.

2. Pollution of groundwater: This statement is correct. Riverbeds naturally act as a filter for water percolating into the groundwater. Removal of sand and gravel, which are natural filters, can reduce the riverbed's ability to filter pollutants. This allows contaminants from the river water to easily seep into and pollute the groundwater table. Additionally, mining activities themselves can introduce pollutants.

3. Lowering of the water-table: This statement is correct. Excessive sand mining deepens the river channel. A deepened riverbed can lead to a drop in the water level of the river, which in turn reduces the recharge of the surrounding aquifers. Consequently, the groundwater table in adjacent areas can decline, affecting wells and vegetation dependent on that water.

Therefore, 2 and 3 are correct consequences of heavy sand mining.