By Viju Mangalore- Daijiworld News Network Mangalore

Mangalore, Mar 26: Come monsoons and activists for conserving water go full swing in propagating rainwater harvesting (RWH). While the simple methods of using percolation pits and facilitating rainwater to reach ground water level is proved to be a cost free harvesting method, a new school of thought based on scientific studies proves this futile.

Contradicting major elements of the knowledge disseminated by RWH experts including Shree Padre, an extensive study undertaken by Dr S G Mayya, professor and dean, Planning and development, National Institute of Technology-Karnataka, Suratkal, has astonishing facts.

Mayya who studied the nature of the ground water level in the last 50 years proves that micro level water harvesting was useless in the coastal region of DK.

The region on the west of Western Ghats in the Peninsular India experiences an average annual rainfall over 3,500 mm. Still it is very common to observe more than 80 per cent of the area experiencing water scarcity particularly during the summer months of March to May.

“Laboratory investigation show that the hydraulic conductivity in the horizontal direction in a laterite formations is almost twice than that in the vertical direction. Further, analysis of observed data clearly establishes that the groundwater recharge takes place and the water table raises to almost near to ground surface every year. Hence, conventional rainwater techniques may not be useful,” explains Mayya.

Recharging of ground water level is taking place by itself and does not require any physical digging of percolation pits, the study proves. The surface flow in the rivers recedes very fast after monsoon. In the similar manner, the groundwater flow to the sea takes place. As a result, there will be sudden draw down in the water table. Hence, the rainwater harvesting techniques required should prevent this outflow from the groundwater reservoir to the sea, than recharging ground resources, Mayya claims.

The laterite rocks are pores and thus water flows to the sea twice as fast as water reaches the ground water level from the surface.

The question is obvious that if micro level water harvesting does not help then what should be done? To this, Mayya has a solution. “Suitable methods for maintaining groundwater include series of vented dams at appropriate places along with a series of subsurface barrier at carefully selected places in the basin. The observed results in the area upstream of existing vented dams justify the suggestion.
Hence, it can be established very clearly that the water harvesting techniques are site specific and it cannot be advocated that the various techniques in practice elsewhere can also be adopted in the coastal region.”

To the question why does our groundwater level decreases, Mayya’s study states that groundwater level and reserves in the coastal region towards west of Western Ghats in peninsular India has gone down leading to groundwater mining. This apprehension is mainly attributed to over exploitation of these hidden resources by indiscriminate sinking of borwells through various schemes of the Government. Further, it is also said that there is no effort for recharging of groundwater reservoirs. It is argued that natural replenishment of groundwater is not enough to build up the groundwater table.

Individuals, NGOs and the governmental agencies have taken up the task of educating the public in artificial recharge techniques. Conventional methods of groundwater recharging, such as spreading, use of percolation tanks, macro level recharging pits are advocated at all possible platforms. Rainwater harvesting techniques proposed in regions of scanty rainfall and impervious soils are proposed in mass scale. Roof water harvesting techniques, which are effectively practised elsewhere, are also proposed in large scale.

Well it is true that inspite of heavy rainfall in the region, it is often experiences acute shortage of drinking water, particularly during the summer months of March and May. It is also true that large quantity of water flows to the sea during monsoon months. The research undertaken explains this phenomenon.
It is observed that the groundwater table fluctuates alarmingly, reaching low ebb to the extent of more than 10 to 20 m in some places. It is true that borewells are sunk indiscriminately, even in areas very close to the shore.

To augment these findings, Prof Mayya has also undertaken RWH in the NITK campus.

To know more about Prof Mayya visit
http://appmech.nitk.ac.in/sgmayya.htm