Environment  
Water Harvesting: Let's Do It
by V.K. Joshi

Everyday we read in the newspapers about water harvesting schemes and sometimes also about their failures. Such schemes fail because often those implementing them are unaware about behavior of water.

Harvesting water involves a bit of engineering, geology and more of common sense. Techniques of harvesting vary from place to place, depending on the geological set up, geographical location and geomorphology of the area. For the purpose of water harnessing our country can be broadly divided in to four units. First is the mountainous terrain which includes the Himalayas, and mountain ranges of the Vindhyachal, Aravallis and the peninsula. Second are the vast Indo-Gangetic plains, and the sandy stretches of the coasts which are the major storehouse of sub-surface water. Third is the Thar Desert, which would not have been a desert if water was available. And lastly the rocky plateaus of the Deccan and granitic stretches of peninsular India.

Each of these terrains has its own peculiarities of geological and geomorphologic set up and one needs to develop innovative techniques as per the rainfall and runoff in a particular terrain.

Water Harvesting in Mountainous Terrain

Jadja is a tiny hamlet in the valley north of Nahan, the headquarters of Sirmur district on H.P. The plight of the villages particularly during the summer months has to be seen to be believed. The village is located on the bank of a dry stream with not a single drop of water around. While establishing camp there I was told that the nearest source is a municipal tap around ten kilometers from the village on road to Nahan. Village women used to trudge that distance daily to quench the thirst of their families. There was a mango tree on the bank of the river opposite the camp. The tree was unusually lush green in that dry belt. A slight probe revealed the presence of a spring that had dried on the surface, on the river bed, close to the tree. A rectangular pit measuring one meter cube was got made near the spring and the base of the pit was covered with a layer of about 50 cm thick layer of 'gravel'.

By next morning the pit was full of absolutely clean and cool water from the spring. The villagers were amazed. They had been told that their village had been cursed and they will never have water close by.

This was just an example to explain that a little bit of ingenuity can work wonders many times.

Water problems of valleys, slopes and ridges of mountains vary as per the location. The valleys are better off because the run off water from the slopes finds its way down to the valley. Unlike the alluvial plains water in the subsurface finds its passages through the cracks, fractures, joints and fissures in the rocks. It is difficult to assess exact quantity of ground water available in such terrains.
Compared to plains the average rainfall on the hills is much higher, but so is the runoff. Local farmers know how to make contour bunds on the edges of their terraced fields and check the runoff. They are able to hold enough water on the terraces to cultivate rice. However this practice is fraught with its own risk. Water filled, terraced fields of Madhyamaheshwar in Garhwal Himalayas caused a great landslide in September 1998 that took several lives and damaged several houses its path. One has to take precautions to avoid such mishaps. Technique used in Nagaland for this purpose called as 'Zabo' is much safer as water is not held in one terrace for long, thereby pore pressure on the edges of terraces is reduced and mishaps avoided.

Habitats on the mountain ridges always face drinking water crisis.

Increased population plus floating population during tourists season adds to the problem. During the course of surveys in the Himalayas apart from the traditional methods of water harvesting on the ridges, two unique water supply systems were seen at Nahan and Subathu in H.P.

At both places the earlier 'Raja' had laid pipelines from far off locations to the town. Water traveled by gravity. 'Pani Sarver Chowki' the source of water supply to Nahan is located about 27 km north. The pipeline has to cross two valleys to reach the collection tank at Nahan. Since it is a supply by gravity it is most cost effective. Such schemes need a perennial source of water, plus the pipeline supplying water needs to be checked continuously for pilferage.

Springs are vital for the habitats of mountain terrains. Chamdungra is a small hamlet in Pithoragarh district of Uttarnchal. Nestled in Limestone hills, in 1963 this place was green and abundant with honey, local agricultural produce and milk products. During a trip with the geologists of the University of California in 2003 it was found the hamlet had turned almost desolate. Greenery along with the honeybees and cattle had vanished. The limestone country has profusion of springs. Unfortunately the springs at Chamdungra were dead because some enterprising engineer had plastered all the outlets of the spring with cement and a pipe had been thrust in, which was connected to a PVC tank. Ostensibly the idea was to store water in the tank. But since the natural outlet had been grouted with cement spring water was lost in the oblivion. As per the government's orders a hand pump had been installed about 500 meters below on the roadside to provide some relief to the villagers. Hand pumps in hilly terrain need detailed studies before installation. But in Uttarnchal one finds them anywhere on the roadside irrespective of the suitability or otherwise of the site.

Villagers are neither geologists nor engineers, but they have the common sense required to keep the spring flowing. 'Jal Panchayats' in villages will go a long way to solve water problem.

Such mistakes all over the mountain terrains are proving costly. The springs emerge at places where softer or more fractured and jointed rocks are underlain by massive rocks. However, the discharge of the springs is dependent on the rainfall too. We all know the climate cycle is changing and rainfall is erratic. In addition most of the pathways of the springs have been choked by anthropogenic activities.

Best course is to revive the surviving springs. It has to be done at local level by the society. In case the society banks on the government then the spring's fate will be like the one at Chamdungra.

An affluent couple from Delhi bought a beautiful cottage away from the hubbub of Almora town on the northern edge of the ridge amidst a pine forest. It was a real bargain for them and a dream house. On occupancy they realized the reason for the low cost. There was not a drop of water around and the pipes laid by the government department were dry.

Immediately they got a huge tank about 6mX3mX3m built and a channel was made along the periphery of the sloping roof. This channel was connected through a pipe to the tank through a filter. To their pleasant surprise they found that once it started to rain, they had enough water in the tank for the remaining part of the year to manage a decent living.

In other words roof top rain water harvesting for the habitats situated on the ridges and high slopes is ideal way to meet the water scarcity. Artificial recharge of aquifer in such terrains may be of no use; because once water enters subsurface it will be lost in the labyrinths of joints and cracks. One has to store harvested water. The storage tanks can be lined with polythene sheets of thick gauge and that water can be used for gardening, toilets etc. Proper lined tanks or Ferro-cement tanks can be used for storing water for drinking.

Various types of filters are available in the market to ensure storage of filtered water. Different designs of rooftop rainwater harvesting methods and filters will be discussed in forthcoming issues.

In a nut shell, in the rocky and mountainous terrains run off must be minimized, pathways of the springs kept clean and undisturbed and excess water must not be allowed to stagnate on the slopes to avoid mishaps.

Runoff water from the hill slopes finds its way to the rivers. These rivers on reaching the plains become gently swaying wide streams. The alluvial plains have been formed by these rivers only and there is a strong affinity between the rivers and the plains. Water harvesting and artificial recharge of aquifers are the keys to solve the water woes of the thirsty plains. Read about it in the next issue.       

July 9, 2006

Image : Rooftop rainwater harvesting in the mountains. (Courtesy ICIMOD)

Previous : The Art and Science of Water
Next : Alluvium: Nature's Store of Water 

 
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