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Water-related development in the basin
Use of water of the Ganges river for irrigation, either by flooding or by means of gravity canals, has been common since ancient times. Such irrigation is described in scriptures and mythological books written more than 2 000 years ago. Irrigation was highly developed during the period of Muslim rule from the twelfth century onward, and the Mughal kings later constructed several canals. The canal system was further extended by the British. The cultivated area of the Ganges valley in Uttar Pradesh and Bihar benefits from a system of irrigation canals that has increased the production of cash crops such as sugarcane, cotton and oilseeds. The older canals are mainly in the Ganges-Yamuna Doab (doab meaning “land between two rivers”). The Upper Ganga Canal, beginning at Hardiwar, and its branches have a combined length of 9 575 km. The Lower Ganga Canal, extending 8 240 km with its branches, begins at Naraura. The Sarda Canal irrigates land near Ayodhya, in Uttar Pradesh. Higher lands at the northern edge of the plain are difficult to irrigate by canal, and groundwater must be pumped to the surface. Large areas in Uttar Pradesh and Bihar are also irrigated by channels running from hand-dug wells. The Ganges-Kabadak scheme in Bangladesh, largely an irrigation plan, covers parts of the districts of Khulna, Jessore, and Kusthia that lie within the part of the delta where silt and overgrowth choke the slowly flowing rivers. The system of irrigation is based on both gravity canals and electrically powered lifting devices (Ahmad and Lodrick).
Total area equipped for irrigation in the GBM river basin is estimated to be around 35.1 million ha, of which 82.2 percent in India, 14.0 percent in Bangladesh, 3.3 percent in Nepal, 0.4 percent in China and 0.1 percent in Bhutan. Area actually irrigated is estimated at 34.1 million ha. The equipped areas irrigated by groundwater and by surface water account for 67 and 33 percent respectively.
Of the 29 million ha equipped for irrigation in India inside the GBM river basin, 67 percent is irrigated by groundwater and 33 percent by surface water. The development of sprinkler and localized irrigation in recent years has been considerable, mainly the result of the pressing demand for water from other sectors, a fact that has encouraged government and farmers to find water-saving techniques for agriculture. The Government has offered subsidies to adopt drip systems. Drip-irrigated crops are mainly orchards (grapes, bananas, pomegranates and mangoes). Localized irrigation is also used for sugarcane and coconut. Investment in drainage has been widely neglected in India, and where such investment has been made, poor maintenance has caused many drainage systems to become silted up. On the eastern Ganges plain, investment in surface drainage would probably have a greater productive impact, and at a lower cost, than investment in surface irrigation.
In Nepal, which is entirely located in the Ganges river basin, the area equipped for irrigation was estimated at 1 168 300 ha in 2002, of which 79.5 percent was irrigated by surface water, 19.2 percent by groundwater and 1.3 percent by mixed surface water and groundwater. Seasonal canals accounted for 58 percent of the area irrigated by surface water, permanent canals for 39 percent, and ponds for 3 percent. In 1992, the area equipped for irrigation accounted for 882 400 ha and in 1982 for 583 900 ha. In 1994, 73.9 percent of the area equipped for irrigation was irrigated by surface water, 12.4 percent by groundwater and 13.8 percent by irrigation systems not fully identified. Most irrigation systems use surface irrigation (basin, furrow). Some areas in the hills and mountains use sprinkler irrigation, but no figures are available. In 2005, the harvested irrigated crop area covered around 1 335 000 ha, of which 47 percent consisted of wheat, 36 percent of rice, 4 percent of maize, 3 percent of vegetables, 2 percent oil crops, 4 percent of other annual crops and 3 percent of sugarcane.
China accounts for approximately 138 000 ha of area equipped for irrigation inside the GBM river basin of which 98 percent is irrigated by surface water.
In Bhutan, which is entirely located in the Brahmaputra river basin, most rivers are deeply incised into the landscape and hence the possibilities for run-of-the-river irrigation are limited. The irrigated areas are called wetland in the local classification. This means that they have been terraced for basin irrigation. In 2007, throughout the country these areas were estimated at 27 685 ha, which corresponds to actually irrigated area. In summer, almost all wetland is under rice cultivation. Double cropping of rice is limited to the lowest altitudes where the winter temperatures still allow its cultivation. Where rice cannot be cultivated, wheat, buckwheat, mustard and potatoes are cropped on wetland areas during the winter season. The wetland areas can be cropped during the winter season, though watering of these winter crops is generally limited to one irrigation at the time of land preparation. To a limited extent, farmers have started to irrigate horticultural crops, including orchards, using hose pipes and surface irrigation methods. In 1994, total irrigated cropped area was estimated at 27 900 of which 98 percent is rice and 2 percent potatoes.
In Bangladesh, though the country has abundant surface water resources, particularly in the monsoon season, its flat deltaic topography and the instability of major rivers make large gravity irrigation systems both technically difficult and costly. On the other hand, during the dry season irrigation using surface water has become difficult or practically impossible owing to limited availability. Therefore the use of groundwater for irrigation has become increasingly important. In 2008 the national irrigation coverage was 5.05 million ha, of which approximately 4.93 million ha inside the GBM river basin where groundwater covered 75 percent and surface water covered 25 percent of the total irrigated area. In 1993, the total area of wetlands throughout the country was 3.14 million ha, of which almost 1.55 million ha were cultivated and 1.38 million ha were drained by surface drains. Thus, total water managed area is estimated at 6.59 million ha. Surface irrigation is the only technology used in large irrigation schemes. In 2008, total harvested irrigated cropped area in Bangladesh was estimated at 5.98 million ha, of which the most important crops are rice accounting for 4.34 million ha (73 percent), wheat 0.31 million ha (5 percent), potatoes 0.26 million ha (4 percent) and vegetables 0.24 million ha (4 percent).
Because of the low-lying topography, each year about 18 percent of Bangladesh is inundated during the monsoon season. During severe floods the affected area may exceed 37 percent of the country and in extreme events like the 1998 flood about 66 percent of the country is inundated. Floods are caused by overspills from main rivers and their distributaries, overspills from tributaries and by direct rainfall. Flood control works can reduce floods from the first two, but only drainage can have any effect on the latter two. The basic benefit of drainage is water control – supply as well as removal.
The particular benefits can be: i) potential increase in cropped area through earlier drainage; ii) higher yields from transplanted Aman rice through early planting; iii) crop diversification in the wet season through better drainage; and iv) more control over crop calendars and patterns through control of the water regime. In 1964, a master plan was initiated for water resources development. This envisaged the development of 58 flood protection and drainage projects covering about 5.8 million ha of land. Three types of polders were envisaged: gravity drainage, tidal sluice drainage and pump drainage. Flood control and drainage projects have accounted for about half of the funds spent on water development projects since 1960. They include:
- Large-scale projects such as: Coastal Embankment Project (949 000 ha), Manu River Project (22 500 ha), Teesta Right Embankment (39 000 ha), Ganges-Kobadak Project (141 600 ha), Brahmaputra Right Flood Embankment (226 000 ha), Chandpur Irrigation Project (54 000 ha), and Chalan Beel Project (125 000 ha).
- Medium-scale projects such as: Sada-Bagda, Chenchuri Beel and Bamal-Salimpur-Kulabasukhali projects implemented under the Drainage and Flood Control Projects (DFC I to DFC IV) and financed by the World Bank. These projects typically cover areas of 10 000–30 000 ha and involve flood control and drainage with limited irrigation development.
- Small-scale projects such as those implemented under the Early Implemented Project, the Small-scale Irrigation Project and the Small-scale Drainage and Flood Control Project.
Total water withdrawal in the GBM river basin is estimated at 373.928 km3, of which 68 percent is groundwater and 32 percent surface water. Irrigation withdrawal accounts for 337.728 km3, or 90 percent of the total withdrawal. India’s total withdrawal inside the GBM river basin has been estimated around 328.2 km3, of which 90.4 percent (296.7 km3) for agriculture. In Bangladesh, in 2008 total water withdrawal within the GBM river basin was estimated at about 35.0 km3, of which 88 percent (30.7 km3) was for agriculture, 10 percent for municipalities and 2 percent for industries. Approximately 79 percent of the total water withdrawal comes from groundwater and 21 percent, from surface water. In Nepal, in 2005 total water withdrawal was estimated at 9.79 km3, of which 98.2 percent (9.61 km3) for agriculture, 1.5 percent for municipalities and 0.3 percent for industry. In Bhutan, in 2008 total water withdrawal was estimated at 0.338 km3, all surface water. This represents a mere 0.43 percent of the annual renewable water resources. About 94 percent of this water withdrawn (0.318 km3) was used for agriculture, while the municipal and industrial sectors used 5 percent and 1 percent respectively. Total water withdrawal of China inside the GBM river basin has been estimated around 0.6 km3, of which 67 percent (0.4 km3) for agriculture.
In Nepal, total dam capacity is estimated at 85 million m3, although potential for at least 138 km3 exists. Hydroelectricity accounted for more than 96 percent of total electricity generation. Theoretical hydropower potential is estimated at about 83 000 MW. However, the identified economically feasible potentials are about 40 000 MW (Biswas, after 2006). The two main diversion barrages are the ones of Kosi and Gandaki reservoirs.
In Bhutan, several large dams were constructed for hydroelectric power generation. These include the 40 m high Chhukha dam (CHPP) on the Wang river in Chhukha district in the southwest, the 91 m high Tala-Wankha dam further downstream on the Wang (Raidak) river near Phuntsholing town, the 33 m high Kurichhu dam on the Kuri river in Mongar district in the east, the Basochu dam (BHPP) near Wangduephodrang town in the centre-west. The 141 m high Punatsangchu dam on Puna Tsang river downstream of Wangduephodrang town is under construction. Total hydropower generation capacity was 477 MW in 2006, of which 336 MW from the Chhukha hydropower plant, 60 MW from the Kurichu hydropower plant and 24 MW from the Basochu hydropower plant. Hydropower represented 96 percent of the country’s electricity generating capacity and 99.9 percent of its electricity generation in 2006. With the commissioning of the first two units of the Chhukha hydroprojects in 1986, and the other two units in 1998, the electricity generation capacity has substantially increased and Bhutan became a significant exporter of electricity to India. With the commissioning of “Tala Hydro Power Project” in 2006, there is a substantial improvement in the energy generation of the country.
The expansion of hydropower production capacity in Bhutan has had an enormous impact as by the end of the Ninth Five-Year Plan (2002-2007), the energy sector contributed to around a quarter of GDP. With a further doubling of capacity envisaged by the end of the Eleventh Five-Year Plan (2014-2019), the energy sector will probably contribute close to half of GDP. The following hydroelectric projects have been identified for future development:
- Mangdue Chu Hydroelectric Project was planned in the Ninth Five-Year Plan (2002-2007) and is expected to be completed in the Tenth Five-Year Plan (2008–2013). The project comprises two dams.
- Sunkosh Multipurpose Project (SMP) is the largest proposed hydroelectricity project in Bhutan.
India controls the flow of the Ganges river with a dam completed in 1974 at Farakka, 18 km from the border with Bangladesh. The Farakka barrage is a not very high diversion structure and is not classified as a large dam. During the dry season it diverts water from the Ganges river to the Hooghly river through the Hooghly Canal. The Bhimgoda dam at Haridwar diverts melted snow from the Himalayas to the Upper Ganges Canal, which was built by the British in 1854. This water is used for irrigation and the flow of the river has been greatly diminished.
India is endowed with rich hydropower potential, ranking fifth in the world. The gross hydropower potential was estimated at 148 700 MW as installed capacity, to which the Brahamaputra, Ganges and Indus river basins contribute about 80 percent. The installed capacity of hydropower generation in India is about 22 000 MW (Biswas, after 2006). The total water storage capacity constructed in the country is estimated at 224 km3. Out of the seven larger dams with a reservoir capacity exceeding 8 km3 in India, only the Rihand dam is in the GBM river basin, on the Rihand river (10.6 km3).
No large dams exist in the GBM river basin in Bangladesh. Three barrages have been constructed across the Teesta, Tangon and Manu rivers, which are used as diversion structures for irrigation purposes only.
Table 2 shows important dams in the GBM river basin.