Floodplains of rivers have immense potential for ensuring sustained water supplies for urban settlements if preserved.
Schemes for preserving and harnessing this resource need to be promoted in regions like the Tamirabarani Basin that is facing a water crisis.
How do flood plains help in preserving water?
Rivers today are facing problems of abysmally low flows due to an indiscriminate extraction of water for use in cities, industries and agriculture.
Floodplains are formed over millions of years by the flooding of rivers and deposition of sand on riverbanks.
These sandy floodplains are exceptional aquifers and any withdrawal is compensated by gravity flow from a large surrounding area.
Notably, some floodplains such as those of Himalayan Rivers contain up to 20 times more water than the virgin flow in rivers in a year.
If we conserve and use the floodplain, it can be a self-sustaining aquifer, and the river and floodplain can be preserved throughout.
The ‘conserve and use’ principle demands that annual water withdrawal rate from the aquifer should not exceed the recharge rate.
Drawing out any more water than is recharged can contaminate and eventually finish off this precious resource and hence needs to be checked.
How can the potential of River Tamirabarani’s Floodplains be realised?
‘Palla floodplain scheme’ of Delhi Jal Board, covers a 25 km stretch along Yamuna and is already supplying water for over 1 million people.
Similar potential along other rives can be explored to meet the needs of urban settlements in a sustainable manner – and Tamirabarani presents a good case.
The Potential - Tamirabarani River in Tamil Nadu flows for 100 km through two urban settlements namely - Tirunelveli and Thoothukudi.
The cities have a population of close to a million people, and the water requirement is less than 54 million cubic metres (MCM) per year.
While 25 Km along the bank has been built over, another 75 Km of the river lies along agricultural land parcels.
1 km of this 75 Km stretch on both sides of the river can be preserved as a water sanctuary (floodplains) and used to provide water to towns.
Specific yield of this aquifer is about 15-20% of its volume and if water is drawn sustainably, it can provide 75-90 MCM of water annually.
Hence, there is more water than what is needed by these cities, and by commissioning a system of wells, this resource can be harnessed.
If water is metered and priced at the domestic Delhi Jal Board tariff of Rs. 30 per kilo-litre, annual revenue of Rs.162 crores can also be generated.
Engaging farmers - Preserving the 75 Km floodplain is critical for this scheme, which mandates contracting the concerned farm land owners.
Farmers in the region are having an erratic income presently, and their holdings can be leased by the government for activating the scheme.
Such a partnership with farmers will provide them earn a stable income while simultaneously retaining ownership rights and preserving aquifer.
In addition, farmers can actually continue to grow trees for timber, fruit orchards or nut trees on their land (but not water-intensive crops).
Even the economics of the scheme looks good and the revenue generated by the water board would more than offset the cost of leasing.
The advantages - Ecologically, a water sanctuary would prevent erosion, heal the river ecosystem, and restore the ecological balance in floodplains.
Even after withdrawal, floodplains would have enough water to slowly release back into the river in a lean season, which provides the sustenance potential.
This scheme would also help in curbing illegal extraction of water, curb pollution by industries and encourage better waste management practices.
