III.1.- Conjunctive use Technique for Surface and Ground Water Resources
The conjunctive water use is planned and co-ordinated harnessing of surface and ground waters, so as to achieve their optimal utilisation in a Canal Command Area and to accrue more benefits rather than individual resource utilisation. In India (Punjab State) 9.71 lakhs ha was water logged in 1964, it reduced to 1.69 lakhs ha in 1974 after sinking shallow tubewells. According to the World Bank (1991) in Pakistan, an intensive water logging and salinity problem developed in irrigated areas, as a result of excessive seepage's from canals and irrigated fields.
These were controlled by Salinity Control And Reclamation Project (SCARP), by installing 25 lakhs shallow tubewells, 6 to 10m deep with low capacity pump, achieving two objectives, one for maintaining water levels within safe limits and other providing supplementary source of irrigation. On an average 80,000 ha of the affected land was brought under production every year by this technique.
The results of CGWB Conjunctive water use in irrigation Project areas namely-IGNP Stage-I, Rajasthan, Mahikadana, Gujarat (and Sarda Sahayak, Uttar Pradesh were studied. The Ground Water Flow Model (Modeflow) U.S.G.S. (1984) Package was utilised to simulate ground water conditions by means of input data fed to the computer. The data was calibrated to generate scenarios to evolve different strategies of conjunctive use.
In IGNP State-I Rajasthan area, surface and ground water resources were computed as 4215 and 992 MCM per annum respectively. Four Scenarios were developed.
The scenario utilising 18% of canal water releases i.e. 759 MCM ground water resource have predicted the recharge to be 6982 MCM, in the next 15 years period and area water logged would be 463, 626 and 785 km2 at the end of 5th, 10th and 15th years respectively. This strategy was found to be viable and the model was run for another 15 years period, which showed that the water logged area would increase to 1190, 1698 and 2111 km2 at the end of 20th, 25th and 30th years respectively. It proves that we can only control the pace of spread of water logging but cannot eliminate it even in next 30 years.
In Sarda Sahayak, Uttar Pradesh project area the surface and ground resources were computed as 2178 and 3062 MCM per annum respectively. Four scenarios were generated by modelling studies.
The scenario with the regulated ground water pumpage and roistering of canals with the present cropping intensity of 153%. The model studies have predicted that the water logged area 2269 km² (27%) in November 1992 would reduced to 41.25 km² (5%) in November 2024 A.D. The usage of surface water is recommended to reduce from 1481 to 1016 MCM and ground water increases from 906 to 1356 MCM per annum. By adopting this strategy, it was found that 0-5 m water level zone area would reduce from present 33% to 20% within a decade.
The World Commission on Environment and Development (WCED 1990) rightly quoted that development which destroys the natural resources on which it is based is not the development. It has been universally recognised that irrigation has been a very powerful force in fostering development in many countries. But when and where, it is used injudiciously, it has been a progenitor of environmental hazards of water logging and salinity/alkalinity.
The conjunctive water use has been found to be an effective remedy for these. It can be concluded that the vertical drainage of water logged and salt infested areas, can be made effective by tapping/developing ground water resource by installing shallow tubewells. It will no only provide assured irrigation but also serve as an inbuilt insurance against these hazards.
III.2.- Artificial Recharge of Ground Water Aquifers
This technique has become a pragmatic approach to augment depleting ground water resource. CGWB undertook a pilot project studies in Jawaharlal Nehru University and Indian Institute of Technology Campuses, New Delhi. Four check dams were proposed. Till September 1997, two check dams were completed and studies on first check dam had proved that there was net rise of 5.3 to 11.3 m in the water table in premonsoon 1996 when compared with premonsoon 1995, after construction of the check dam. During 1996 monsoon, 46500 cubic meter water was recharged to ground water aquifers enabling a tubewell run for 24 hours daily during premonsoon 1997. It was working for 4 hours daily before check dam. Moreover, 300 families of four members each could be provided with household water for a period of one year taking a norm of 100 l/capita/day.
The Chinese developed water management by 'four water concept' and achieved an unparalleled expansion of irrigated area from 16 Mha in 1950 to 48 Mha in 1986 to feed 1100 million people by controlling falling water table. It involved aquifer dynamic control by keeping depth of water 1m and 6m below ground level. At the end of rainy season, the water level is the lowest, whereas at the end of dry season the drawdown is not allowed to exceed rechargeable depth through rainfall and surface water. It avoided occurrence of water logging and prevented mining of ground water resources. During rainy season, the main task was to facilitate recharge. At the end of rainy season, water level is not permitted to fall below the depth which could make pumping cost excessive and uneconomical. During dry season, the water level is continuously lowered by pumping for irrigating lands and it is lowered to such a depth that 'storage space' vacated in the aquifer was enough that it could get filled during next rainy spell. The techniques of recharge were spreading rain water on flat topographic lands, recently abandoned gravity irrigation systems and reducing rain water run off by bundling and terracing to improve percolation. In Habie province, this concept was applied in seven irrigation and drainage canals, for 12 km length, piped distribution system 34 km long with 45 tubewells. Mobile pumps were used to pump water from canals in rainy season and ground water during dry season. The pumped water was carried and distributed through pipes.
As a consequence the water level which were previously at a dangerously deep levels were raised and kept within a depth of 2 and 6 mbgl. It has resulted in substantial savings and increased crop yields.
The Central Groundwater Board, Ministry of Water Resources (1996) in their National Perspective Plan for harnessing surplus monsoon run off and to recharge it to Ground water repositories, recommended saturation of vadose zone down to 3 mbgl which will create subsurface storage potential of 49 Mha-m. Out of this, 44 Mha-m is retrievable.
Based on the availability of monsoon run off and storage potential of vadose zone, the feasible ground water storage was estimated as 21 Mha-m, out of which 16 Mha-m will be utilised. This additional subsurface storage will bring substantial area under irrigation.
It will raise water levels by 1.5 to 3 m. Consequent upon rise of water levels due to additional ground water recharge, there will be reduction in the pumping lifts of ground water resulting in saving of energy. It was calculated that there will be annual saving in consumption of diesel about 319 million litres; considering the price of diesel at Rs 9 per litre, the saving comes to Rs 287 crores. The saving of electrical energy would be to the tune of 810 million KWh; taking Rs 5 per KWh, the annual financial saving totals to Rs 405 crores. The benefits of subsurface storage are that it would be free from environmental hazards and interstate controversies, equitable distribution of water resources in water scarce areas, ensuring sustainability of existing ground water abstraction system for major part of year due to extended recharge period of 3 to 4 months mitigating drinking water scarcity and controlling hazards of flash floods, soil erosion and silting of major reservoirs and their channels, thereby increasing life of reservoirs and navigability of river channels.
III.3.- Conservation measures suggested
World is heading for a major water supply crunch Uncontrolled exploitation of ground water and uncontrolled pollution have brought in serious problem of water management. About 44 million people in India have been effected by water quality. Many million household do not have adequate quantity of water. In many rural areas, people have to walk long distances to fetch water.
The rich, ultra rich and the poor get water at highly subsidised rates, at some places water is supplied even free of cost. This paradigm, ensures wastage of water with no incentive for conservation. Many countries have started plans for conserving water. USA has enacted law to restrict toilet flushes to a maximum of 7 litre per flush, instead of conventional toilets 12 litres per flush. It is estimated that a US family of four can save about 85,000 litres of water in one year by this measure. A Golf course use about 3000 cubic meters of water per day. It is computed that this quantity of water is sufficient to met the needs of 15,000 people per day. When large proportion of population do not get even drinking water and we are wasting this precious commodity in golf courses. If we save this water for about 100 days in a year, we will have 3 lakh cubic metres to fed 15 lakh additional people per annum. These points indicate that ground water legislation is the need of our time, to control exploitation and proper use of ground water resources. These simple measures to control wasteful water resource can save and make available a copious quantity of potable and fresh water.