Hydro power is a renewable, economic, non-polluting and environmentally benign source of energy. Hydro power stations have the inherent ability for instantaneous starting, stopping and load variations, improving the reliability of the power system and so are considered the best choice for meeting peak demand.
India is endowed with enormous, economically exploitable and viable hydro potential, assessed at about 84,000MW at 60% load factor (148,700MW installed capacity). In addition, 6,780MW in terms of installed capacity for small, mini and micro hydroelectric schemes have been assessed. Also 56 sites for pumped storage schemes with an aggregate installed capacity of 94,000MW have been identified. However, only 15% of the hydroelectric potential has been harnessed so far and 7% is under various stages of development. Therefore 78 % of the potential remains without any plan for exploitation.
Despite hydroelectric projects being recognized as the most economic and preferred source of electricity, share of hydropower has been declining steadily since 1963. The hydro share has declined from 44% in 1970 to 25% in 1998. The ideal hydro thermal mix should be in the ratio of 40:60. Due to imbalance in this mix, especially in the eastern and western regions, many thermal power stations are required to back down during off peak hours. The capacity of the thermal plants cannot be fully utilised, resulting in a loss of about 4 to 5% in the plant load factor. Even if the share of hydropower is to be maintained at the existing level of 25%, the planned capacity addition from the 9th and 10th plans would work out to 23,000MW. If the share were to be enhanced to 30%, it would require further addition of 10,000MW of hydro capacity.
The constraints which have affected hydro development include difficult investigation and inadequacies in tunnelling methods, deficiencies in providing long term financing, tariff related issues and poor contract management.
The hydro projects are also affected by geological conditions (especially in the Himalayan region), inaccessibility of the area, problems with land acquisition, resettlement of affected families and law and order problems in militant areas.
All the major hydroelectric projects in the Himalayas require extensive tunnelling. The rocks are full of geological surprises and pose a challenge to all the engineers.
Dulhasti HE Project, Jammu & Kashmir
Dulhasti HE Project is a run-of-the-river scheme located on the river Chenab. The project envisages installation of three units, of 130MW each, operating under a net head of 207.5m. The annual energy generation from the project is estimated at 1928Munits in a 90% dependable year.
The project includes construction of a 65m high concrete gravity dam, a 10.57km long 7.70/7.46m dia head race tunnel, a 240m long ‘Dufor Type’ desilting basin, a 90m deep and 18.25m dia surge shaft, a 311.6m long 7.7m/6.7m dia pressure shaft, and an underground powerhouse to accommodate three Francis turbines and a 307m long, 7.46m dia, horse-shoe shape tailrace tunnel. The project was originally scheduled to be commissioned in July 1994 but, law and order problems, and stoppage of work by the earlier civil works contractor, it is unlikely to be completed before December 2003.
Chamera HE Project Stage II, Himachal Pradesh
The 300MW Chamera HE Project, Stage II, is a run-of-river project being constructed on the river Ravi, located near Chamba. It is an upstream development of the Chamera Stage I project (540MW) commissioned by NHPC in April 1994. The project will generate 1500Munits of energy in a 90% dependable year.
This project incorporates construction of a 39m high concrete dam, a 7.86km long (7m dia) head race tunnel, a 93m high (15.5m dia) underground surge shaft, an underground power house with three Francis turbine generators of 100MW each operating under a head of 243m, and a 3.6km long (7m dia) tailrace tunnel. This project is scheduled for completion in May 2004.
Dhauliganga HE Project – I, Uttar Pradesh
The 280 MW (4 x 70MW) Dhauliganga HE Project – I is being constructed on the river Dhauliganga, a tributary of Sharda (Kali) river in Pithoragarh district. The project site, Chirkala, is 360km from the nearest broad gauge rail heads.
The project is to operate under a net head of 302m. This will generate 1134MU in a 90% dependable year and will provide peak support to the northern grid.
The project includes construction of a 56m high concrete faced rockfill dam, a 5.4km long (6.5m) dia headrace tunnel, an underground powerhouse with four Francis units of 70MW each, and a 445m long tailrace tunnel (6.5m dia) to discharge the waters back into the river Sharda.
All the works currently are in an advanced stage of construction. A diversion tunnel has been completed and the river diverted. The excavation of the main tunnel is on schedule and project is due for completion in March 2005.
Teesta Stage III HE Project, Sikkim
Teesta stage III is a 1200MW, run-of-the-river scheme including a 103m high gravity dam and an 8m dia, 13.5km long diversion tunnel.
The water will drop 800m to the surge shaft and powerhouse underground on the left bank of Talung chu. Other features of the project are an 8m dia, 440m long diversion tunnel, three 300m long desilting chambers, a 123m high, 20m dia surge shaft, three 4.75m dia, 1,385m long steel lined pressure shafts and an underground powerhouse for six Pelton wheel turbines.
Teesta Stage IV HE Project, Sikkim
This project includes construction of a 88.5m high gravity dam and diversion of the river Teesta through three 6m dia intake tunnels. Also planned are three 220m long desilting chambers of varying width, a 10.99km headrace tunnel, a 26m dia and 160m high open surge shaft, and three 4.8m dia steel lined pressure shafts. An underground powerhouse will accommodate three vertical Francis turbines. A D-shape 7m wide access tunnel has also been proposed which bifurcates into two D-shaped tunnels, each 7m wide, for the machine hall cavern and transformer cavern, respectively. Both caverns are connected to each other by 5m x 5m cable tunnels for access and carriage of bus ducts.
Teesta Stage V HE Project, Sikkim
Teesta Stage-V Project is a run-of-the-river scheme which includes a 95m high gravity dam for diverting the water through a 17.67km long tunnel and vertical pressure shaft by utilising a gross head of 216m for generation of 510MW of power. Two diversion tunnels, both 12.2m dia, and 473m and 610m long respectively, are also being constructed on the right bank of Teesta river to divert the river to allow for construction of the main dam. This has a five-gated spillway and is of special importance due to the excavation of the thick pile of riverine material from the riverbed to expose a foundation for dam. A 9.5m wide horseshoe shape headrace tunnel will carry water from the intake to the powerhouse. A 92 high and 30m dia surge shaft, located at the end of the tunnel, will trifurcate into three 4.7m steel lined vertical pressure shafts. Two adits, one at the top and another at the bottom are also planned for the construction of pressure shafts/penstocks. Three 6m wide, 165m long D-shape tailrace tunnels are proposed. Excavation of both diversion tunnels, intake area and adits are underway.
A full description of the project will appear in a future issue of T&T International.
Teesta Stage VI HE Project, Sikkim
The diversion dam to be constructed across the river Teesta about 500m upstream of the existing bridge at Mamring/Khanitar will be a 76m high structure with an overall length of 324m.
Since this is a concrete gravity dam, the diversion of river water has only been considered for during non-monsoon when the floodwater will be allowed to overflow the constructed portion of the partially raised blocks. Once the sluice spillways are constructed flood water will pass through these. Two independent hemispherical cage type intake structures, of 13m radius, have been provided on the right bank, about 150m upstream of the dam.
Water drawn through the intakes is supplied to four underground desilting chambers, at 25m spacing, through 6m dia tunnels. The chambers, each 21m wide at the centre, 26m deep, with a hopper at the bottom, and 400m long provide the most economical flow velocity (0.28m/s) for eliminating particles of 0.2mm and above in size. Silt settlement in the chambers is collected by flushing conduits, which are ultimately lead to a 5.8m wide D-shaped flushing tunnel.
The dia of the headrace tunnel for a design discharge of 506m³/s has been worked out to be 12m. The tunnel is about 3.5km long, circular in shape and at a grade of 1 in 300. Two 8m dia, D-shaped adits will be provided at the ends of the headrace tunnel to facilitate construction.
An underground restricted orifice type surge shaft, 35m dia and 76m high, has a 100m long expansion chamber at an elevation of 338m. Four steel lined pressure shafts have also been planned, one for each unit, with a designed discharge of 126.5m³/s. Each pressure shaft is 5.2m in diameter with 7m centre-to-centre spacing.
The underground powerhouse complex comprises a machine hall cavern, transformer cavern, access tunnel, cable and ventilation tunnel, inter-connecting tunnel, escape tunnel and draft-tube tunnels. The size of the machine hall cavern is 100m long, 20m wide and 47.75m high. A service bay is provided at one end. The machine hall will house four Francis turbine units, each of 90MW.
The transformer cavern is 110m long, 25m wide and 28.8m high. A 8m x 8m D-shape tunnel is for access to the powerhouse cavern. The machine hall and transformer caverns are connected via a gallery 9m wide and 9m high. Four D-shaped tailrace tunnels, 8.5m x 8.5m, are for discharging the water back to the Teesta river.
Parbati HE Project Stage I, Himachal Pradesh
The Parbati HE Project Stage I, with a proposed installation of 3 x 250MW, is located in the Kullu district. It is a storage scheme proposed to harness hydroelectric potential of the upper reaches of the river Parbati. Dicharge of Tosh nallah is also to be utilised for power generation. On completion, the project will provide annual energy generation of 2,800Munits in a 90% dependable year. The project requires construction of a 180m high rock-fill dam sited neasr Dibi-Bokhri village, a 14.5km long, 4m dia, circular headrace tunnel and underground powerhouse located at Nakthanfor three units of 250MW each. The nearest railhead and airport are located at Kiratpur and Bhunter respectively. The project is scheduled for completion in eight years from the date of government approval.
Parbati HE Project Stage II, Himachal Pradesh
Parbati HE Project Stage II is a run-of-the-river scheme on the river Parbati, a tributary of the river Beas in the Kullu district. The annual energy generation from the project in a 90% dependable year is 3175.92 Munits.
The project includes construction of a 91m high gravity dam, a 1.25m wide trench weir, a 546m long feeder tunnel to divert waters of Jigarai Nallah to a reservoir, and a 31.25km long, 6m dia headrace tunnel. Also in the project are diversion and desilting works on Hurla, Pancha, Manihar and Jiwa Nallahs for augmentation of waters in the headrace tunnel through drop shafts to a 116m high, 17m dia restricted orifice bifurcating into 675m long, 2.75m dia branches to a surface power house with four Pelton turbine generators, each of 200MW, operating under a net head of 787m. Four tailrace channels, 60m long and of 5m x 4.5m section each, will carry waters to the river Sainj.
The project is scheduled to be completed in ten years from the date of start, including pre-construction works.
Parbati HE Project Stage III, Himachal Pradesh
On completion the project will yield four hours daily peak support and an annual energy generation of 1997Munits in a 90% dependable year. It includes construction of a 75m high concrete gravity dam, a 9.91km long, 7.5m dia headrace tunnel and surface powerhouse to house three units of 167MW each. Completion is scheduled for eight years from the date of government approval.
Kishanganga HE Project, Jammu & Kashmir
This project is a storage scheme on the river Kishanganga, a tributary of Jhelum. The estimated annual energy generation will be 1025MU in a 90% dependable year. With water from Kishanganga, the generation of downstream projects will be increased by approximately 501Munits.
The project comprises a 103m high gravity dam, 5.3m dia, 24km long headrace tunnel, a 15m dia and 127m high surge shaft, 3.5 dia and 998m long pressure shaft and an underground powerhouse to house three Pelton wheel turbines generating 110MW each. A tailrace system comprises a 4.1m dia, 746m long D-shape tunnel, a 4.1m dia D-shape 121m long cut-and-cover portion and 111m open channel. Project completion is planned in nine years from the date of government sanction.
Uri II HE Project, Jammu & Kashmir
This has been envisaged as a run-of-the-river scheme on the river Jhelum. The project is planned immediately downstream of the existing Uri I project, commissioned by NHPC in May 1997, with a powerhouse at about 2.4km downstream of Uri I tailrace.
The project will include a diversion structure with a spillway section to the left side of the river, a head regulated to the right side, a desilting basin in the right bank, a headrace tunnel about 2.4km long in the right bank, an underground powerhouse complex in the right bank, and a tailrace tunnel about 9.1km long. The project is scheduled to be completed in six years from government sanction.
Sewa II HE Project, Jammu & Kashmir
Sewa HE Project Stage II is a run-of-the-river project with pondage capacity provided only at the diversion dam. Estimated annual generation in a 90% dependable year is 323Munits.
The project comprises a 41m high masonry and concrete diversion dam across the river Sewa near Gatti, a headrace tunnel of 3m dia and 10.2km long, a 12m dia, 125m deep desilting chamber, a restricted orifice type surge shaft, a 3m dia inclined pressure shaft trifurcating into branches to feed three generating units, an underground powerhouse for three Pelton turbines generating 40MW each, and a D-shape (4m x 4m) 600m long tailrace tunnel. The project is expected to be completed in four years from the date of government approval.
Pakal Dul HE Project, Jammu & Kashmir
The Pakal Dul HE Project is planned as a run-of-the-river scheme on Marusudar, the main tributary of Chenab river in Doda District. The project comprises a 77m high concrete gravity dam, a 7m dia, 14.78km long headrace tunnel, an 8.2m dia 110m deep surge shaft, two pressure shafts of 4.4m and 3.75m dia, an underground powerhouse (197 x 23m x 47m) to house five generators of 200MW each and a 7m wide, D-shape, 250m long tailrace tunnel. The project is scheduled to be completed in eight years
Bursar HE Project, Jammu & Kashmir
The proposed Bursar HE Project is located on the river Chenab. The nearest rail head is Jammu which is 350km away from the project site. The estimated annual energy generation from this in a 90% dependable year is 1626Munits. After completion, there will be an increase in generation of Salal and Dulhasti HE Project of 949Munits in a 90% dependable year during the non-monsoon period.
The project comprises a 252m high rockfill dam across the river Marusudar, a 10.5m dia and 4.7km long horseshoe shape headrace tunnel; a 28m dia, 194.6m deep surge shaft, four pressure shafts, 4.8m dia and 370m long, an underground powerhouse, and two 8m dia, D-shape 50m long tailrace tunnels. It is proposed that the project be completed in nine years from the date of government approval.
Nimoo-Bazgo HE project, Jammu & Kashmir
Situated in Ladakn district, the project’s nearest railhead is at Jammu and nearest airport Leh. It is a run-of-the-river scheme on the Indus about 600m downstreamn of its confluence with the river Zansar.
The project includes construction of a 92.5m long river diversion barrage, a 4.94km long headrace tunnel to the surge shaft, and an underground power complex for four vertical Francis turbines of 7.5MW capacity. Water from each draft tube goes to a 95m long, 7.3m dia tunnel discharging eventually to the river. The project is scheduled for commissioning 7 1/2 years after government sanctioning.
Nathpa Jhakri HE project, Himachal Pradesh
The Himalayan region with its five river basins, provides ample scope for development of hydropower. Out of the five basins, Satluj has the highest potential at about 9227MW, out of which only 1332MW has so far been exploited.
Nathpha-Jhakhri HE Project in Kinnaur and Shimla district, will harness the hydropower potential of Satluj basin. The site is located in the lower Himalayas which has very rugged topography with lofty hills. The area is dissected by deep, narrow valleys and gorges which have steep cliffs and escarpment faces.
Plans include construction of a 60.5m high gravity dam for diverting water through a 27.3km long 10.15m dia, headrace tunnel. The rock exposed in the foundation and abutments of the dam consists mainly of gneiss, augen gneiss, biotite gneisses with amphibolites and pegmatites as intrusives. Three pressure shafts of 4.9m dia of varying length from 571 to 622m originate from the bottom of a surge shaft. This is 301m deep, with a restricted orifice and variable dia of 21m and 10.2m. An underground powerhouse cavern of 222m x 20m x 49m will be located at Jhakri to generate 1500MW.
The east-west headrace tunnel has biotite gneiss, augen gneiss and granitic gneiss with pegmatite, amphibolite and biotite schist as subordinate bands in the eastern part of the tunnel. In the western part, schists, amphibolites and quartzites with subordinate gneissic bands are present.
The work in this project is in an advanced stage of construction. Widespread damage from flash flooding is now being rectified.
Conclusion
Of late, the main thrust has been in developing hydroelectric power to rectify the balance of the hydro/thermal mix in the country. The development of hydro power in the Himalayan region involves a lot of tunnelling and poses a challenge to tunnelling engineers.
The latest state-of-the-art equipment and methodologies are being used to construct the projects in a time bound schedule. The above projects are required to be completed in the next decade or two which will increase the capacity for hydroelectric generation.
