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Local Water Harvesting Systems: Shree Padre |
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Chellanam is a coastal belt in Ernakulam district of Kerala. Fresh water is difficult to come by here. Piped water that comes from far away is not dependable. Some times people have to collect drinking water even at midnight.
The poor fishermen of this region have developed an inexpensive and tank less method of storing water. The system works on the principle of a lower density fluid floating on higher density fluid. Thus, fresh water that has a lower density than brackish water forms a layer above the latter, if poured slowly. A shallow well is dug near the house. Rainwater collected on rooftops is released into this well after filtration through a down pipe pierced with small holes. The fresh water is lifted with a hand pump when needed. Care is taken while fitting the system to ensure that the pipe drawing water to the hand pump is kept slightly above the pipe feeding rainwater to the well. Use of motors is discouraged because it agitates the water and mix the brackish layer with the fresh one. It requires some experience to position the hand pumps correctly. After installing the PVC pipes, the well is refilled with sand. This method of rooftop rainwater harvesting has now become popularly known as the ‘Chellanam method’. The system can be adopted only in seashores where the water table is rather shallow and it is brackish.
In Wayanad district of Kerala, since time immemorial, adivasis have been harvesting rainwater simply by guiding it over leaves tied to a coconut or jackfruit tree trunk. Erecting a pandal made of bamboo splits is another method, as also tying a sari as a pandal for four wooden poles to guide the rainwater to the desired location is equally effective. Both - the Chellanam and Wayanad systems are still in vogue and are effective only during monsoons.
Filter well is another fast and inexpensive water harvesting system. In Cheruvathur, Kasargod district of Kerala an estimated 50,000 filter wells are functioning. They are possible only in the sandy layers of the seashores. Filter wells are dug manually and are shallow- between15 to 20 ft. Points where fresh water would be available are located by experience. Initially with the help of auger and later with a sand scooping device, a vertical bore hole is dug till they get potable water. After this, a perforated PVC pipe covered with coir rope is inserted, with a hand pump fitted on top. Filter wells are used for both drinking and irrigation purpose. Though the water is mainly drawn with hand pump, there are cases where a small electric motor is also used for irrigation. Filter wells can be dug by two people within a few hours. In Thirthahally, Chitradurga, Tumkur region of Karnataka, filter wells dug into river banks and old courses of rivers. It has been observed that wherever water extraction is controlled in such regions, filter wells serve as long as there is substantial rain water percolation into the sandy layers of soil.
Horizontal bore wells are another source of potable water. Generally, such wells are dug inside a dug well when the latter almost dries up. Unlike machine-drilled vertical bore wells, these do not pierce the rocky layer and the underground aquifer. It draws water from the shallow layer of earth just like a dug-well. It is inexpensive and cannot go beyond 80 ft or if it encounters a rock in its course. Another advantage is that the same water lifting device, maybe a pulley & rope or centrifugal motor that used to lift water from the dug well earlier can be used after digging horizontal bore wells too. Each horizontal bore has a water source of the size of a cigarette. In Dakshina Kannada district of Karnataka, they are being dug manually.
In Indi and Sindhagi taluks of Bijapur district of Karnataka, such horizontal bore wells have been so popular since 1970’s that even the local banks give loans for the purpose. Here the bore wells are dug with diesel engines. The method for both, the mechanized as well as manually dug horizontal bores is similar. The drilling bit is pushed inside the selected point. Once it enters the hole, another small pipe is fitted to its back. Water is sent inside this pipe to wash out the dug out soil.
After the publication of articles on the two types of horizontal bore wells in Adike Patrike, a farm publication in Kannada, farmers at Raichur adopted this system. Initially specialist mechanics were invited from Coimbatore. Within a few years about 60 such horizontal wells have been dug inside the tanks that have helped augment shrinking water resources in the arid regions of Thirthahally.
In Kundapur area of Dakshina Kannada, Karnataka, bore well are being dug vertically. Chandran, a mechanic has made alterations to the usual drilling bit of the oldest slow rig. This drilling bit has a diameter of two feet. With the help of a diesel engine or electricity motor, he digs the bore-hole inside the dug well till it reaches the rock. If in the process, the bore well succeeds in intercepting any water vein, due to its pressure, the water level inside the dug well increases. A perforated PVC pipe is inserted into the bore-hole and blue-metal pieces are packed around it to permit free entry of water inside the pipe. This whole process is cheaper than deepening the whole well.
Such is the success rate of bore wells, both horizontal and vertical, inside dug wells that more and more people are going in for them - sometimes even more than one. However, a word of caution. These ‘water augmenting wells’ cannot be taken as permanent if sufficient rainwater harvesting is not carried out in the catchment area. Else, these ‘new’ sources of water would also dry up in due course of time if there are no small rain pits all over the catchment area. (shreepadre@sancharnet.in) |
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| Volume No. |
Honey Bee, 17(1) & (2): 32-33, 2006 |
