Thread: Varahamihira, the 6th century polymath has 125 verses on groundwater in Brihat Samhita:
"Even as there are veins in the human body, so too are in the earth, some of them running higher, some lower."
So true, esp for hard-rock aquifers! From a book by EAV Prasad PhD.
Varahamihira lived in Avanti (MP), and wrote the encyclopedic 'Brhat Samhita' (~The Vast Collection). Its 54th chapter is called 'Dakargalam' (~Groundwater Exploration).
Amazingly, there's no water dowsing! Instead it uses ecological patterns as indicators of GW.
Most emphasis is on certain vegetation as an indication of shallow GW.
Phreatophytes are plants that depend on water from saturated zone (below water table). Here is the piture of a Pipal tree, seeking water.
In US, Cottonwood trees are a similarly used as GW indicators.
Varahamihira describes tens of trees, and factors like their branching patterns etc to predict the direction and depth of groundwater.
Predictions include precise directions and numbers, which are questionable. But it must not be harshly judged by today's standards.
The lack of grass in a grassy area in this shlok, may be alluding to water logging.
It talks about other factors like palm trees with two crowns, thornless individual in the midst of thorny trees, glossy leaves, unusual fruits etc.
It mentions whiteness in certain sap-exuding trunks, which may be due to higher root pressure.
Termites are also mentioned widely to predict the presence of groundwater.
There have been some (not too rigorous) modern studies which corroborate that termites have a strong preference for sub-surface water. It probably prevents them from desiccation.
EAV Prasad has written a book and numerous on the subject. Someone handed me down this decades old booklet which contains reviews for the book.
There is much to be learn from traditional ecological knowledge for sure.
#Thread: Peninsular rivers in India are drying up at a phenomenal rate. Some of them dry up immediately after a flood! This not natural for India's relatively wet climate.
Here's an explainer on the contribution of Groundwater baseflow in keeping our rivers flowing.
These pictures illustrate the plight of some of our major rivers:
PC: bit.ly/2OJCLNQ
This is how catchments should respond to rain:
1st pic: Rain events in a US watershed
2nd pic: Corresponding streamflow events
Almost all the water below the red line is GW's contribution. Without it, you'd see flow only when it rains - THE NEW NORMAL in many rivers.
While the 2018 NITI Aayog report saying Delhi will run out of groundwater by 2020 was a misunderstanding, a district less than 100 km from Delhi has almost exhausted its freshwater.
Here is a #thread on salinisation of GW of Mewat/Nuh district of Haryana. Dilli zyada door nahi:
Map from a recent paper by Krishan et al (2020) in the reputed Journal of Hydrology.
Salinity of more than 2 gm/L is considered unfit of drinking & general irrigation.
Only blue in map is freshwater and it REDUCES from 14% to 1% of the area over the monsoon! Why reduce?
Freshwater region reduces because pumping is happening in central/freshwater area reducing its water level, saline water from south increases further in monsoon, and ingresses the freshwater.
This is a very dangerous trend that Dr. Himanshu Kulkarni has predicted for Punjab too.
Limestone often dissolves in the groundwater (a process called karstification), creating much more space & hydraulic conductivity. Space for water is denoted by Specific yield = % of vol of water/rock.
@CGWB_CHQ here gives values for Specific Yield for as carbonates 2-15%:
Some widely used carbonate aquifers are in Chhattisgarh, Cuddapah & Vidhyan sedimentary basins; and in Kashmir.
Kashmir is famous for prolific springs ('nags') some of which discharge at over 3000 lps! These are basically underground rivers curring through limestone like butter.
Thread: Delhi has a lot of GW, as its on a thick alluvial aquifer formed by Yamuna. But the GW situation is grave because most of the GW is salty (Orange in map) & unusable!
Snippets from the recent National Project for Aquifer Management (NAQUIM) report by @CGWB_CHQ
This map shows thickness of fresh-water left. If you have lived in areas of west Delhi like Dwarka you would know how salty the groundwater is.
This map shows how over a decade the water levels (top/freshwater) have decreased. Decrease of ~ 2 meters on an average.
Unsustainable considering that the remaining freshwater thickness is less than 10 meters in many areas.