Imagine what would have happened to life on the earth without rains! It is a dreadful thought isn't it! Had there been no clouds and no rainfall, perhaps neither you would have been reading these lines nor would I have been there to write them.
Rains are the best gift the Mother Nature could bestow upon us. It is a renewable gift. Water is life. On the earth we have two types of water resources, the surface water resource like the rivers, lakes, ponds and snow, ice and glaciers and the sub-surface or groundwater resources. Both these types of resources are part of the hydrologic cycle, which begins with evaporation of ocean waters to form the clouds and under certain conditions lead to rain or snow on the earth. Clouds are the nature's wonderful desalination plants!
Water from the rain or snow that reaches the earth again travels back to the oceans. However, part of this water also reaches the subsurface to add to our groundwater resource. Majority of the people remain ignorant about how the subsurface water is stored! Water that penetrates the topsoil in alluvial country percolates down between the grains of sand as a film. This film can continue to travel down, but for the pervious and impervious nature of the subsurface strata. As soon as this film reaches a layer of fine sand or silt the rate of movement is slowed down. In case it meets an impervious layer like clay the bedrock, it can not travel any further.
When a boring is made or a well is dug, the film of water in the sand termed aquifer finds an empty space and occupies it immediately. This is the water that we tap and either pull it to surface in buckets from a dug-well or pump it out through a hand pump or a tube-well.
In a rocky terrain like Karnataka or Tamilnadu, the depth of soft rocks like sand is much less compared to Indo-Gangetic Alluvium. Once the subsurface water reaches the rocky strata it goes haywire, because rocks are impervious and they have cracks, fissures and joints, water is lost as it travels through them.
The hydrologic cycle has been going on since times immemorial and will go on till eternity.
Then where is the problem? Why this hullabaloo about water scarcity? Well problem is there because in many areas either due to natural reasons the resource is not being recharged or water being consumed or withdrawn is much more than being recharged by the nature. Under normal circumstances water is a renewable natural resource. But when we start actually mining it or if there is an overdraft, the water budget goes in the red.
Mother Nature though unpredictable, always follows a set pattern. It is we who fiddle with the system and make things complicated for us. Nature is not bound by any political boundaries. It is all pervasive. If forests are hacked in Nepal there are more floods in Bihar. More floods means more silt is added to the topsoil. Silt being finer obstructs percolation of surface water down into sub-subsurface reservoir. This was just an example.
The recharge of aquifers takes place through rains only. Rainfall in our country is governed by the monsoon winds. Monsoon literally means a wind system that undergoes a seasonal 1800 reversal of direction. Compared To other countries, the geomorphology of the country makes the Indian monsoon unique. Himalayan mountains on the north act as a barrier and do not permit the monsoon winds to escape and the land in the tapering peninsula has sea on both sides, thus enriching the monsoon winds.
The average rainfall in India is about 120 centimeters. But it is highly variable from place to place. While the northeastern part of the country receives an average annual rainfall of about 1000 cm, parts of Rajasthan desert get even less than 15 cm rainfall. What is important to know is that more than 75% of total rainfall is received in 100 to 120 days of the year. These days or months of monsoon are vital from the point of view of water harvesting.
Part of this rain water enters the groundwater regime and rest reaches the rivers through surface run off. In its course of flow a river cuts across several types of strata. Some draw water from the river and others supply water to the river. For example, there is hardly any rainfall in the Western Ghats of India for eight months. Yet the river Krishna carries a sizeable discharge all through the year. This is because of the groundwater runoff along the course of the river, which maintains a steady flow. Similarly during the dry season almost entire water of Ganga from Haridwar is diverted to Upper Ganga Canal, yet further downstream, near Narora the River Ganga apparently remains unaffected by the diversion. This is again because the river bed has springs which maintain the discharge of the river.
Areas of perpetual deficit rainfall or drought affected areas face the problem of natural ground water recharge. Anthropogenic interference particularly in the inhabited areas lowers the water table to such an extent that the original level is not regained. Development and aquifer recharge are apparently at daggers drawn. Development in our society implies concretization of the cities. Rainwater can not penetrate concrete, it has no option but to follow the natural slope and reach a river or waterlog the townships till it evaporates. It is sad that while developing housing colonies land capability is never assessed. Tube-wells are sunk without knowing the ground water budget of the area.
In order to tackle the problem ideal situation would be to harness all the water from the skies and divert it for recharging the aquifers in the subsurface or refill the dry ponds or store it by other means for future use. Possibilities are several and depend upon the need, geo-morphological set up of the given area and of course the cost-benefit ratio.
While the techniques would be discussed in the subsequent issues, it is worth knowing why the Indian society is apathetic towards water management. Agenda Singh the renowned water-wizard of Rajasthan stated in a recent talk that one of the root causes of this apathy is the State's take over of water resources. As long as it was maintained and manned by the society the problem was not so acute. He advocates 'Pani Panchayatsa' run by women to manage the water resources. He has proved that mobilization and motivation of the people can lead to greening of dry areas and it is possible to make a dry river low once again.
Watch out for the next issue to read more on water harvesting.