In his beautiful poem har desh mein tu, Sant Tukdoji says, “saagar se uthaa baadal ban ke / baadal se phutaa jal ho kar ke / phir nehar banaayaa nadiyaa gahari / tere bhinna prakaar tu ek hi hai.” (You arose from the oceans as clouds / You fell from the clouds becoming rainwater / Then You made deep rivers / Your forms are many but You are indeed One.)
A poetic description of the water cycle, a phenomenon you study in your geography and environmental science classes in school.
Water returning from the atmosphere to Earth is called “precipitation.” Santji talks only of rain here. However, precipitation has many forms – liquid (rain), solid (snow, hail), and sleet (mixture of rain and snow in some places; mixture of ice, snow, and freezing rain in others).
When rain reaches Earth, it’s ‘rainwater.’ Some of it flows on the surface (we call this ‘surface runoff’) and joins other bodies of water (rivers, streams, canals etc. to eventually reach either a lake or a sea).
The rest of the water goes underground through the soil and loose rock – a process called ‘percolation’ (just like in a south Indian coffee filter!). When it reaches hard rock, it stops and collects in underground water bodies called aquifers (“those which carry water”) – imagine an underground lake.
“An aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, or silt) from which groundwater can be extracted using a water well.”
The top of this water is called the ‘water table.’ When you draw water from traditional wells using a pot, you are taking it from the water table. When you use a bore-well or hand-pump, it pulls up this sub-terranean (Latin, sub = under; terra = ground) water or ‘groundwater’.
Sometimes underground water flows as sub-terranean rivers. Occasionally, these rivers are accessible through holes dug into the ground. This is how the desert civilizations of ancient Persia (modern Iran) flourished – using a water management system (called qanat to channel water from underground streams. A version of this was at one time in use in Kasargod (Kerala) and Dakshina Kannada (Karnataka) districts and was called suranga (Samskrtam for tunnel)
Sometimes the underground river may emerge above ground and run like a surface river. The Lost River (50km long) in West Virgina, USA is an example.
Recently, scientists reported a vast underground “river” about 4km underneath the Rio Amazonas (Spanish and Portuguese for the Amazon river; Rio = river in both languages) in South America. Amazonas is the world’s largest river (not the longest; Africa’s Nile river is the longest). (‘Amazonas’ derives from the name of a tribe of legendary woman warriors.)
Amazonas is 6,400km long, discharging about 209,000 cubic metres per second, and has a basin over 7 million sq. km.
The report of the underground river (for now, it’s called Río Hamza) estimates that this river is 200km – 400km wide (compare: distance from Bangalore to Chennai is about 330km). Hamza’s discharge is estimated at 3,900 cubic metres per second – much lower than the Amazon. But there is still a lot of disagreement on whether Hamza is actually a river in the usual sense.
Sometimes, human engineering forces water to flow underground. These artificial underground ‘rivers’ are used to control surface flooding. Example: Neglinnaya River under Moscow, Russia.
In all cases, remember, pollution on Earth’s surface gets into the water under our feet!
Download a worksheet (available in three formats) relevant to this post:
- Water underfoot – worksheet – pdf version
- Water underfoot – worksheet – docx version
- Water underfoot – worksheet – doc version
Two maps of South America (source: d-maps.com) in .pdf format:
(A version of this post was published in Deccan Herald Student Edition, 22 July 2013, page 1.)