The country is divided into 20 river basins. Basin-wise availability of water in the country is taken from Ministry of Water Resources. It is seen that both in terms of available surface water and average monsoon run-off, Ganga and Brahmaputra are the two largest basins followed by Godavari, Krishna, Indus and the Mahanadi. Because of geographic and topographic constraints, the estimated utilizable surface water (EUSW) in Brahmaputra is considerably low.
The Ganga basin has by far the largest amount of EUSW (250 km3/yr). Because of the large surface area and the alluvial nature of the aquifers, the Ganga basin also has by far the largest (-170 km3/yr) replenish able groundwater resource. This is the amount of groundwater naturally replenished every year and stored within the zone of water-table fluctuations.
The static fresh ground water resource is considered as exploitable ground water available in aquifer zones below the zone of water-table fluctuation. The Ganga basin also has the largest static fresh groundwater (SGW) potential (-7830 km3/yr) followed by the Indus (-1340 km3/yr) and the Brahmaputra basins (-1020 km3 yr). It may also be noted that a part of the SGW reserve is already being exploited in some parts of the country.
If the data given in are examined together with those of commitments already made locally on surface water in the respective basins, it is seen that only Brahmaputra and the west-flowing rivers of the Western Ghats have any significant quantity of monsoon run-off in excess of that already utilized and/or committed for use as Table 4.2 part of ongoing or planned development projects.
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This must be kept in mind while devising any water-resource augmentation/ development strategy.
In general, the following elements seem to form part of a viable long-term water-resource development strategy:
(i) Achieve the full utilizable potential of -1120 km3/yr (SW=690 km3/yr;GW=430km3/ yr) to meet the anticipated demand (1182-1450 km3/yr).
(ii) Convert part of static groundwater potential to dynamic potential by over-exploiting aquifers and artificially recharging part of monsoon run-off in excess of utilizable surface potential to these aquifers.
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(iii) Increase irrigation leading to increase in dynamic storage of ground water through exploitation/recharge of aquifers.
(iv) Reuse and recycle industrial and municipal wastewater.
(v) Transfer from basins with surplus water to basins with deficit potential.
(vi) Import agricultural produce– virtual water.