Conjunctive use of ground and surface water, a technology well developed and tested elsewhere (particularly in California, Ohio and many other parts of the US), could bring about a major revolution in the management of our water resources in Northern India. In addition to creating the basis of vast new economic opportunities, including huge increases in food and energy production, improved flood and drought control, river transport year-round, better salt balance and port maintenance, it would provide ecosystem services of the highest value, transforming the lives and well-being of an entire nation.

In a seminal paper entitled "The Ganges Water Machine", published nearly thirty years ago in the prestigious American journal Science (9 May 1975, Volume 188, pp 611-616 – reprints of which are available from the editor), Roger Revelle and V. Lakshminarayana showed how a carefully designed but simple method of creating underground storage of water along the rivers of the Ganga Basin could lead to dramatically better use of the region’s resources. This would produce massive increases in food production (by as much as a factor of three, they estimated at the time), more uniform flows of river waters throughout the year, lessening the possibilities of both floods and droughts, and the consequent improvements in downstream river quality. These, in turn, would lead to huge new opportunities for improving both the economy and ecology of the region.

Here, in italics, are some excerpts from the original paper:

The fundamental problems of land and water development in the Ganges Plain arise from the highly seasonal flow of the river and its tributaries. Nearly 84% of the rainfall occurs from June through September, and 80% of the annual river flow takes place during the 4 months of July through October.

The method used to find the depression (or lowering) of the water table during low flow seasons is given below:

The drawdown due to pumping in an acquifer is given by

Equation (1)

The advantages identified by the authors included: increased water available for irrigation during the rabi crop, reducing the huge seasonal variation in the flows of the tributaries and the main river, greatly reduced losses by evaporation, and all the consequent benefits for river transport, waste dilution, downstream uses, etc.

To work properly, the Ganga Water Machine must be designed properly. The authors provide the hydrological science that underlies this technology, which shows that the primary interventions required are the building of carefully spaced "well fields" on either side of the nallahs, canals and tributaries, and operating them so as to pump down the aquifers during the dry season and thus raising the surface stream flows considerably. During the monsoons, the five measures identified above to increase infiltration will refill the aquifers.

Obviously, considerable energy is needed to run the Ganga Water Machine, but work by Development Alternatives has shown that only a small fraction of the irrigation water generated would be sufficient to grow the biomass needed to power the Machine. The revenues in terms of additional agricultural production alone would be much larger than the costs of all the energy required.

Table depicting possible river reaches for underground storage of monsoon flows

The accompanying equations and graphs give a glimpse into the mathematics underlying the working of the technology, showing that within a period of 3 or 4 years, a properly functioning Ganga Water Machine could establish a regime where the the ground water table would have been drawn down sufficiently to allow its conjunctive use with surface water to yield major improvements in the year round availability of these resources. The Table, taken from the original paper, gives an idea of the magnitude of the underground storage and lean season flow improvements possible for some of the tributaries of the Ganga – showing more than 10 Million hectare metres storage – comparable to the amount used for irrigation in the entire basin today.