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Evaporation control is achieved by either physical or chemical or any other other techniques. Presently, the evaporation models do not lay additional emphasis on controlling measures. Under the Indian conditions the typical annual reservoir evaporation loss is of the order of 160 cm. The hydrological water balance equation based on the continuity concept [Mutreja, 1986]is as follows:

P + I_c + I_g = Q + E_T + O_c + O_g + S_m + S_g + S_d + L(2)

where, P : precipitation
I_c : surface inflow into basin through channels,
Q : runoff
I_g : groundwater inflow into the basin,
E_T : evapotranspiration
O_c: surface outflow from basin thro’ channels,
S_m : soil moisture change
S_g : change in groundwater storage
S_d : change in depression storage and
L : loss through deep percolation. In Equation (2) above, we can improve the values of S_m, S_g and S_d by minimising Q, E_T, O_c, O_g and L. This is what is essentially achieved in any rainwater harvesting system. This has the capability to overcome the water scarcity situations. Rainwater harvesting is the universally recommended technique in which attempts are made to conserve rainwater wherever it falls by creating surface and sub-surface storage. Various rainwater harvesting techniques such as those through percolation pits for individual houses, permeable beds for building complexes, ponds, wells cum canals, open wells, service cum recharge wells, defunct bore wells, sub-surface storage created due to broken bricks method, cisterns, underground sumps, drinking water jars, surface and sub-surface water tanks, artificial glaciers, long underground tunnels, surface water reservoirs created by check dams and so on need to be considered as per their suitability [Ramakrishnan, 1998].

In addition to these techniques, there are other appropriate conservation practices which need to be encouraged and inappropriate depletion or wasteful practices which need to be strongly discouraged. These include:

1. Educating the water users about low cost/quantity and high benefit/quality alternatives and thereby to promote a cautious utilization approach from ‘wash basin level’ to the ‘river basin level’.
   
   
2. Strongly encouraging the use of rainwater of not so good quality for non-drinking purposes discouraging the ‘groundwater mining’ (i. e., over-exploitation of groundwater).
   
   
3. Promoting better irrigation practices like sprinkler irrigation (even for paddy cultivation) [Sivanappan, 2000] and drip irrigation and preventing wasteful practices like flooding or furrow irrigation.
   
   
4. Adopting appropriate techniques for preventing losses such as deep percolation of groundwater and thereby to ensure a favourable water balance.

Concluding Remarks
Water is a very scarce commodity and unless it is properly managed, one can not avoid adverse and paradoxical situations such as temporal scarcity in above-average rainfall areas and lack of drinking water due to pollution or contamination of abundant water in general. In all such cases, there is always a scope for developing/adopting appropriate water management strategies either involving RS/GIS or otherwise which can ensure a favourable benefit-cost ratio as well as an acceptable water use efficiency. One of the shloka from the Indian Epic ‘Mahabharata’ ‘….Pranetavyam Vichakshanaih’, meaning ‘….needs intelligent control’ should serve as the guiding principle for us always and everywhere [Subramanya, 1986].

References

1. Grolier Inc. (1997), ‘Israel’, Lands and Peoples, Volume 2, p.4-5, 104-115, Danburry, Connecticut, USA.
   
   
2. Joshi, S., (1998), ‘Waterworks India’, Down To Earth, Oct. 15, p. 34-37, Centre for Science and Environment, New Delhi, India.
   
   
3. Kumar, A., (1998), ‘Waterworks India’, Down To Earth, Oct. 15, p. 22-32, Centre for Science and Environment, New Delhi, India.
   
   
4. Rao, K. L., (1979), India’s Water Wealth, p. 4-16, Orient Longman Ltd., Hyderabad, Andhra Pradesh, India.
   
   
5. Subramanya, K., (1994), Engineering Hydrology, p. 169-172, Tata McGraw Hill Ltd., New Delhi, India.
   
   
6. Mutreja, K. N., (1986), Applied Hydrology, p. 799-800, Tata McGraw Hill Ltd., New Delhi, India.
   
   
7. Ramakrishnan, S., (1998), Groundwater, p. 722-734, Chennai, Tamil Nadu, India.
   
   
8. Sivanappan, R. S., (2000), "Strategies in Surface and Ground Water Management’, Eighth National Water Convention, Feb. 9-11, p. 169-176, National Water Development Agency, New Delhi, India.
   
   
9. Subramanya, K., (1986), Flow in Open Channels, p. VI, Tata McGraw Hill Ltd., New Delhi, India.

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