UPSC Prelims 2018 · Question 81 of 99

UPSC Prelims 2018 question on River Sand Mining Consequences

Which of the following is/are the possible consequence of heavy sand mining in river beds?

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.

  1. 1 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3
Show answer

Answer: B. 2 and 3 only

Analysis

Consequences 2 and 3 follow, so the answer is (b) 2 and 3 only.

Statement by statement

Statement 1 is INCORRECT, and it reverses the effect. Depletion of sand in the streambed and along coastal areas deepens rivers and estuaries and enlarges river mouths and coastal inlets, which may lead to saline water intrusion from the nearby sea. Salinity therefore rises rather than falls.

Statement 2 is CORRECT. Sand mining affects the adjoining groundwater system and the uses local people make of the river, and turbidity increases at the mining site.

Statement 3 is CORRECT. A sand aquifer helps recharge the water table, so sand mining causes water tables in nearby areas to sink, leaving drinking water wells on the embankments dry.

Source

Peer reviewed study on the effects of instream sand mining (reference material).

How to crack it

Sand in a riverbed does two jobs, holding water for recharge and holding back the sea. Remove it and both fail, which yields a falling water table and rising salinity in one step. Statement 1 is the standard reversal trick, so when a statement claims an extractive activity improves a water quality parameter, suspect the direction has been flipped.

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