Rainmakers and Keepers
8 Oct 2013 7:29 PM GMT
India has some 195 million hectares of land under cultivation of which 63 per cent are rain-fed. Around 45 percent of food-grain production is through rain-fed lands of the country. Bulk of the projected additional production of food-grain has to come from rain-fed lands. We need to go in for inexpensive practices to make this possible. Over many generations, our farmers have developed the infrastructure for Kharif cropping over millions of hectares of land. It would be unkind if this amazing demonstration of their ability without government help is underestimated. The socio economic and political changes after independence have somehow slowed down their initiative and have made them oriented towards outside help. It is time they were reassured of their ability and wisdom and empowered to manage the rain that falls on their land.
If we talk in the context of the vast regions of our country which are located in the high rainfall zone, the aggregate volume of the created storage capacity cannot hold more than 15 per cent of the total volume of precipitation. Around 85 per cent of the rainfall is being lost in various ways. Through surface run-off we lose about 40 per cent; bulk of it even while it is still raining. We should be able to enhance infiltration into the soil in situ and prevent drought in the uplands of inland areas and minimise the incidence of flood in the plains. More than 35 per cent gets lost through evaporation.
We need to appreciate that soil mass being a porous medium, can absorb the entire precipitation if we allow it adequate time. The aggregate volume of porosity is 2-3 times the volume of precipitation received in a village. Thus storage space provided by nature is more than adequate. The limiting factor is the time for in-filtering the desired quantum. Under the current situation, it hardly stays for about 30 minutes.
Not much can happen within such a short time because the rate of infiltration is only 75mm per hour. If we want 750mm, which the volumetric water requirement for a cropping intensity of 200 per cent, the quantity of runoff required to be in-filtered must stay within the village for at least ten hours.
Many areas of the country depending on rain fed farming have hilly lands and reasonably rich forest cover. Forests are a natural in-filtering agent of rainfall. They facilitate storage of rain water and ensure its slow release throughout the year. Many of the villages in these regions had forest around them and benefited from spring flow from the forests.
Through traditional wisdom, the entire area of the village was used to grow different kinds of crops including rice and sugarcane. Villagers grew a variety of pulses and raised flourishing orchards. The plains thereby received only moderated floods where the soil was regularly enriched with silt deposits. Vanishing forests have left huge land mass behind, which is still in the same shape as it was when forest cover was there. These can be reshaped to create an alternative flow path, which will be long enough to touch all uplands and flow long enough to slow down the speed of water so as to gain the needed ten hours to in-filter at least 750mm of rainfall.
Clay, the finest soil particles, has the property of adhering to each other and form a crumbly structure when it comes in contact with water. If each elementary particle is a tiny sphere, there will be some space between them when two touch each other. This space is called a micro pore. When water enters into these pores, it gets so firmly held that even gravity cannot remove it. It can only be extracted by plant roots.
Once in-filtered, water stays in the micro pores and can be used for plant life. Each of these crumbs forms a larger sphere and can attach to each other as such leaving larger gaps between them. These gaps are called macro pores. Water can be stored in them as well. Difference is that it can be moved by gravity in the direction of the hydraulic gradient. Normally, nature fixes this direction in a given situation. Due to this property, water can move from an upper location to a lower one. If one finds the direction undesirable, it can be changed. Therefore human intervention is needed only to in-filter more and more water into the soil.
The sub-soil water moves almost at the same rate at which the rain water in-filters into the soil i.e. 75mm per hour. This speed is 30,000 times slower than the average speed of surface runoff. At this slow speed, water will travel only 1.8 meters per day, which means it will remain inside a village for more than a year.
In other words, the next year’s rain would have arrived before the last drop of rain water would have drained out of the village. At present the rainwater stays for about 30 minutes within a village. This should be extended to at least 10 hours to achieve retention of 750mm. To achieve this, the length of travel should be increased and gradient causing flow decreased. This can be done by retaining rainwater inside the plots as long as possible and, when necessary, spilling to the side plot instead of plot below. There will be no out flow from the village during normal showers.
Run-off /out flow during prolonged showers will be so much regulated that there will be no scouring of drainage channels. However, if necessary, underground cut-off/diaphragm wall shall be provided at the outfall point of draining line to present loss of groundwater from the village/watershed.
The technique required to ensure this, does not disturb the present land configuration of the village and, therefore, eliminates the problem of land acquisition/rehabilitation. The whole village becomes drought free and the water table rises to such an extent that Rabi crop become possible. Low lands become fit for summer paddy. The entire aquifer below becomes saturated and dilutes the ground contamination to such an extent that water becomes fit for drinking. All the ponds and tanks in the village remain full throughout the year.
After the rain stops, the stored water is released slowly to the drains as off season flow thus making available water to villages in lower reaches. This creates enough employment opportunities inside the village thus reducing seasonal migration. The required soil engineering work can be taken up over all the lands of each village. There is no masonry work involved. This programme can easily be undertaken through the national employment guarantee programme.
The author is former Coal Secretary
If we talk in the context of the vast regions of our country which are located in the high rainfall zone, the aggregate volume of the created storage capacity cannot hold more than 15 per cent of the total volume of precipitation. Around 85 per cent of the rainfall is being lost in various ways. Through surface run-off we lose about 40 per cent; bulk of it even while it is still raining. We should be able to enhance infiltration into the soil in situ and prevent drought in the uplands of inland areas and minimise the incidence of flood in the plains. More than 35 per cent gets lost through evaporation.
We need to appreciate that soil mass being a porous medium, can absorb the entire precipitation if we allow it adequate time. The aggregate volume of porosity is 2-3 times the volume of precipitation received in a village. Thus storage space provided by nature is more than adequate. The limiting factor is the time for in-filtering the desired quantum. Under the current situation, it hardly stays for about 30 minutes.
Not much can happen within such a short time because the rate of infiltration is only 75mm per hour. If we want 750mm, which the volumetric water requirement for a cropping intensity of 200 per cent, the quantity of runoff required to be in-filtered must stay within the village for at least ten hours.
Many areas of the country depending on rain fed farming have hilly lands and reasonably rich forest cover. Forests are a natural in-filtering agent of rainfall. They facilitate storage of rain water and ensure its slow release throughout the year. Many of the villages in these regions had forest around them and benefited from spring flow from the forests.
Through traditional wisdom, the entire area of the village was used to grow different kinds of crops including rice and sugarcane. Villagers grew a variety of pulses and raised flourishing orchards. The plains thereby received only moderated floods where the soil was regularly enriched with silt deposits. Vanishing forests have left huge land mass behind, which is still in the same shape as it was when forest cover was there. These can be reshaped to create an alternative flow path, which will be long enough to touch all uplands and flow long enough to slow down the speed of water so as to gain the needed ten hours to in-filter at least 750mm of rainfall.
Clay, the finest soil particles, has the property of adhering to each other and form a crumbly structure when it comes in contact with water. If each elementary particle is a tiny sphere, there will be some space between them when two touch each other. This space is called a micro pore. When water enters into these pores, it gets so firmly held that even gravity cannot remove it. It can only be extracted by plant roots.
Once in-filtered, water stays in the micro pores and can be used for plant life. Each of these crumbs forms a larger sphere and can attach to each other as such leaving larger gaps between them. These gaps are called macro pores. Water can be stored in them as well. Difference is that it can be moved by gravity in the direction of the hydraulic gradient. Normally, nature fixes this direction in a given situation. Due to this property, water can move from an upper location to a lower one. If one finds the direction undesirable, it can be changed. Therefore human intervention is needed only to in-filter more and more water into the soil.
The sub-soil water moves almost at the same rate at which the rain water in-filters into the soil i.e. 75mm per hour. This speed is 30,000 times slower than the average speed of surface runoff. At this slow speed, water will travel only 1.8 meters per day, which means it will remain inside a village for more than a year.
In other words, the next year’s rain would have arrived before the last drop of rain water would have drained out of the village. At present the rainwater stays for about 30 minutes within a village. This should be extended to at least 10 hours to achieve retention of 750mm. To achieve this, the length of travel should be increased and gradient causing flow decreased. This can be done by retaining rainwater inside the plots as long as possible and, when necessary, spilling to the side plot instead of plot below. There will be no out flow from the village during normal showers.
Run-off /out flow during prolonged showers will be so much regulated that there will be no scouring of drainage channels. However, if necessary, underground cut-off/diaphragm wall shall be provided at the outfall point of draining line to present loss of groundwater from the village/watershed.
The technique required to ensure this, does not disturb the present land configuration of the village and, therefore, eliminates the problem of land acquisition/rehabilitation. The whole village becomes drought free and the water table rises to such an extent that Rabi crop become possible. Low lands become fit for summer paddy. The entire aquifer below becomes saturated and dilutes the ground contamination to such an extent that water becomes fit for drinking. All the ponds and tanks in the village remain full throughout the year.
After the rain stops, the stored water is released slowly to the drains as off season flow thus making available water to villages in lower reaches. This creates enough employment opportunities inside the village thus reducing seasonal migration. The required soil engineering work can be taken up over all the lands of each village. There is no masonry work involved. This programme can easily be undertaken through the national employment guarantee programme.
The author is former Coal Secretary
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