UPSC PRELIMS 2020 : Study on Floods

Study on Floods

Topic: Study on Floods

Topic in Syllabus: Indian Geography

 

Study on Floods

Destabilising geological processes, coupled with extreme rainfall events and unscientific farming and construction activities, pose a serious threat to human habitation in the highlands of kerala according to scientists.

 

Findings:

A team of scientists from the National Centre for Earth Science Studies (NCESS) here who carried out an investigation in the wake of the heavy rain and devastating floods  had found that land subsidence, lateral spread, and soil piping were an immediate threat to life and property in the uplands.

 

Soil Piping

Piping occurs when water erodes beneath the surface of the ground creating an underground tunnel known as soil pipe. This usually begins as small pores underground and are enlarged with increase erosion, in some instance these hole may be even large enough for a person to crawl through.

In areas where there are cracks in the soil or areas of less resistance , water will start to move through creating; a void. Eventually after constant erosion the surface layer of the ground will not have any support beneath and thus collapse creating a depression

In some other instances; the soil pipe can be formed from openings in the ground that has been left behind when plants died or trees have been uprooted

Animals can also help create soil pipes by burrowing and tunneling in the soil. These voids provide an opening for moving water and create ideal situations for soil pipe formation.

Soil piping is a common feature along side river bank leading to river bank failure. As water seeps beneath the river bank it creates an alternate route, this is eroded and shaped by the water forming a channel (soil pipe). As more water seeps into the bank, the soil becomes heavier and more likely to break apart making it prone to erosion and failure. Soil piping has been related to earth dams failure, dike failures and formation of sink holes.

Soil piping is a natural process, but;often human induce activities may result in change in surface and underground water flow and result in increased subsurface erosion and making soil pipe a potential risk. Soil pipe collapse may become a threat to farming and can threatened the stability of a building.

 

Land Subsidence

Land subsidence is the lowering of the land-surface elevation due to changes that take place underground.

It is the sinking of the sub surface soil caused by sub surface erosion, often triggered by unscientific land use and drainage

 

Lateral Spread

Lateral spread occurs when soil on a gentle slope start moving downhill. It is caused by a process called as liquefaction

When soil looses strength due to saturation it behaves like fluid triggering a flow. Lateral spread is progressive and spreads rapidly, often culminating in a complex landslip

 

Sample Question:

Consider the following statements about Global Soil Biodiversity Atlas.

  1. It is prepared by United Nations Convention to Combat Desertification (UNCCD).
  2. India is among countries whose soil biodiversity faces the highest level of risk.
  3. Soil biodiversity encompasses the presence of micro-organisms, micro-fauna and macro-fauna.

Which of the above statements is/are correct?

a) 1, 2

b) 2, 3

c) 1, 3

d) 1, 2, 3

 

Solution: b)

India’s soil biodiversity is in grave peril, according to the Global Soil Biodiversity Atlas prepared by the World Wide Fund for Nature.

The WWF’s ‘risk index’ for the globe — indicating threats from loss of above-ground diversity, pollution and nutrient over-loading, over-grazing, intensive agriculture, fire, soil erosion, desertification and climate change — shows India among countries whose soil biodiversity faces the highest level of risk.

Soil biodiversity encompasses the presence of micro-organisms, micro-fauna (nematodes and tardigrades for example), and macro-fauna (ants, termites and earthworms).