Roger Revelle and V. Lakshminarayana , 

 (1975) 611-616. 



29a 

 'The Ganges Water Machine," Science 188 



Present Needs for the Ganges 

 Low Flow 



The Ganges Water Machine 



Roger Revelle and V. Lakshminarayana 



fbe river Ganges and its tributaries, 

 •jjd the flat and fertile plain through 

 ^jjjch they flow, are one of earth's 

 •rtat natural resources. For thousands 

 jf years abundant water and generous 

 land have provided the foundation for 

 I highly developed civilization based on 

 jgriculture and for one of the world's 

 largest concentrations of human popu- 

 lations. But farming is mainly tradi- 

 tional and at a subsistence level, with 

 little surplus, and as a result the popu- 

 lation has remained overwhelmingly 

 jural and most people are desperately 

 poor. Although irrigation from canals 

 and wells has been practiced for mil- 

 lennia, chiefly as a protection against 

 the uncertainties of the monsoon rains, 

 the water resources are largely un- 

 tapped; the small fraction of water used 

 for irrigation is poorly managed and its 

 productivity is low. 



Deeply embedded cultural, social, 

 and economic problems inhibit modern- 

 ization of agriculture and fuller utiliza- 

 tion of the water resources. Capital 

 investments and technological changes 

 on a large scale are also required. As 

 experience elsewhere shows, the intro- 

 duction of technological changes on the 

 required scale might break the chains of 

 tradition and injustice that now bind the 

 people in misery and poverty. 



Ganges and Its Tributaries 



The Ganges Basin covers parts of 

 four countries, India, Nepal, Tibet, and 

 Bangladesh; eight Indian states, Punjab, 

 Uttar Pradesh, Haryana, Himachal 

 Pradesh, Rajasthan, Madhya Pradesh, 

 Bihar, and West Bengal; and the Union 

 Territory of Delhi. We shall consider 

 that part of the Basin that drains into 

 Bangladesh through the great distribu- 

 ^ called the Padma. The other main 

 distributary, called the Bhagirathi, has 



Roger Revelle Is director ol the Harvard 

 ^""r for Population Studies, Cambridge, Mas- 

 l^nusetts 02138, and V. Lakshminarayana is 

 p^'stant professor of civil engineering at the 



lad, 



I ''Jd( 



'*n Institute of Technology, Kanpur, Uttar 

 'esh. 



long been moribund and now serves 

 only as a spill channel for Ganges 

 floods. Within India, the Ganges Basin, 

 as we have defined it, covers 800,000 

 square kilometers (i). Its population is 

 about 225 million, somewhat more than 

 that of the United States, which covers 

 nearly ten times the area. At present 

 rates of growth, the population will 

 .double in 30 years. 



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 percent of the rainfall occurs 

 from June through September, and 80 

 percent of the annual river flow takes 

 place during the 4 months of July 

 through October. 



The average annual flow of the 

 Ganges at the Hardinge Bridge in west- 

 ern Bangladesh is 36.2 X I0« hectare- 

 meters, and the monsoon flow from 

 July through October is 28.9 X lO^ 

 ha-m. During the remaining 8 months 

 of the year, the river carries only 

 7.3 X 10" ha-m (2). Part of this dry- 

 season flow comes from groundwater 

 in the Ganges Plain, and the remainder 

 comes mainly from the Himalayas. 



Even at present, the dry-season flow 

 of the Ganges is barely sufficient for the 

 needs of India and Bangladesh. If irri- 

 gation with either groundwater or sur- 

 face water continues to be developed 

 along the lines of present programs, the 

 dry-season flow will be continually re- 

 duced. In order to develop the full irri- 

 gation potential of agricultural land 

 without unacceptable reduction of the 

 dry-season flow of the Ganges, it will 

 be essential to store a portion of the 

 monsoon waters for use in irrigation. 

 Because of the steep slopes of the 

 Himalayan foothills and the flatness of 

 the Ganges Plain, surface sites for stor- 

 age are scarce, and costs per unit vol- 

 ume of surface-stored water arc several 

 times higher than in many other parts 

 of the world. On the other hand, there 

 are great possibilities for underground 

 storage, which should be relatively in- 

 expensive. 



Irrigation in Bangladesh. The average 

 rainfall in Bangladesh is higher, and the 

 potential for increasing groundwater 

 recharge from rain is greater, than in 

 the Indian part of the Ganges Plain. 

 Unfortunately, there is a wide variation 

 among different districts, just as in 

 India. Revelle and Herman (i) esti- 

 mated that water from the Ganges is 

 needed in Bangladesh during the low 

 flow season to supplement groundwater 

 irrigation in three districts in the north- 

 western part of the country. In the 

 southwest, where the groundwater is 

 saline, Ganges water is the sole irriga- 

 tion source. In other districts some 

 Ganges water is needed to minimize 

 saltwater intrusion. The sum of these 

 needs totals about 1.8 X 10* ha-m. 



Diversion of low flow waters for Cal- 

 cutta port maintenance. Part of the 

 Ganges waters during the low flow sea- 

 son must be diverted at the Farakka 

 Barrage through the Bhagirathi into the 

 Hooghly River, to maintain a sufficient 

 freshwater discharge past the port of 

 Calcutta. We learn that the feeder chan- 

 nel at the Farakka Barrage has been 

 designed and constructed for a capacity 

 of about 0.29 X 10« ha-m per month. 

 This is more than half the average low 

 flow of the Ganges during the 3 months 

 of February through April. These are 

 also ihe months when the need for 

 surface water is most critical in western 

 Bangladesh and when the flow into the 

 rivers from groundwater is minimal. 



Navigation on the main stream. Eco- 

 nomic development in both India and 

 Bangladesh would be hastened if the 

 Ganges could be used as a great inter- 

 national waterway for transport of 

 heavy or bulk materials. Conversely, as 

 development proceeds, the needs for 

 year-round water transportation on the 

 river will rapidly grow. A water route 

 down the Ganges and up the Brahma- 

 putra into Assam would yield large 

 benefits today. 



Year-round transportation will de- 

 pend directly on maintaining a sufficient 

 dry-season flow. Even for relatively 

 shallow barges and moderate-sized 

 ships, an average river depth of 5 m 

 would be desirable. With a width of 

 900 m and a velocity of flow of 0.35 m 

 per second, this would require a mini- 

 mum discharge of 1550 m'/sec, or 

 about 3.2 X 10° ha-m during the eight 

 dry months. 



Downstream water quality. The 

 growth of modern agriculture in India, 



