UPSC Prelims 2018 · GS Paper I
Question 81: Environment and Ecology
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 :
AnswerUPSC’s answer is (b).
Heavy sand mining lowers the riverbed, so the river recharges groundwater less and the water table falls. Removing the sand also strips away a natural filter, exposing aquifers to pollution. Near the coast it lets saline water move upstream, which increases salinity rather than decreasing it. So groundwater pollution and a lower water table are consequences; decreased salinity is not.
- 1. Salinity rises as sea water intrudes upstream.
- 2. Removing the sand filter exposes groundwater to pollution.
- 3. Mining lowers the riverbed and the water table.
How you could have got this
- If you were sure statement 1 is not correct, (a), (c) and (d) go: each of them includes 1.
What you needed to know: Salinity rises as sea water intrudes upstream.
Only (b) is left. You didn’t need statements 2 or 3.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Wrong: mining raises, not lowers, salinity.
- (b) Right: groundwater pollution and a lower water table.
- (c) Wrong: statement 1 is false.
- (d) Wrong: statement 1 is false.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2018, General Studies Paper I, Series A. The paper on upsc.gov.in.