NEA COULD MAKE TERRIBLE BLUNDERS
( Upper Trishuli Projects)
By Dr. AB Thapa
It is reported that the NEA is considering to implement the Upper Trishuli A & B Projects According to the Gandak basin Master Plan a single stage development of the Upper reach Trisuli will be the most attractive project. Such development of the Upper Trishuli will allow obtaining a head of about 835 m to generate 300 MW. However, it is also possible to develop the Upper Trishuli in two or three stages. It appears that the NEA is considering adopting the multi-stage option to develop the potential of the Upper reach Trisuli.
Upper Trisuli projects and the project to transfer the Langtang river flow from the water surplus Trisuli basin into the water deficit Bagmati and Kulekhani basins could be construed to adversely affect one another. If we are contemplating to engage private developers to take up the Upper Trisuli projects, we should not provide them with grounds to seek compensation for the reduction of the Trisuli flow as a result of the Langtang diversion to Bagmati and Kulekhani through the Melamchi route. While taking any decision on the implementation of the projects to utilize the potential of Upper reach Trishuli, we should be very careful to insure that the Langtang diversion possibility to augment the Melamchi, Bagmati and Kulekhani flows would not be adversely affected. A brief synopsis of the proposed Langtang diversion project to augment the flow of the Bagmati and Kulekhani rivers is presented hereinafter.
Langtang Diversion
The hydropower generation potential of the Langtang river has been significantly enhanced by a relatively large storage reservoir located in the upper reaches of this river. It can help to provide all through the year an uniform flow of about 15 cumecs in the middle and lower reaches. A total head of about 3500 meters could be utilized for power generation by 4 hydropower stations to be built in a cascade and out of them three power stations would be operating at an exceptionally high head of about 1000 meters or more. It also avails an opportunity to make full use of the existing structures like the storage dam, tunnels, power houses of the Kulekhani No-1 & No-2 hydropowers ever since suffering from acute shortage of water for power generation. The development of the Langtang river would allow us to generate electricity at a rate perhaps the lowest in our region and also to provide drinking water to the Katmandu valley for free.
The Langtang Power Projects
The concept of the Langtang project solely for power generation was developed under the UNDP supported Gandak basin masterplan study . This concept requires some revision to include a new component aimed at supplying drinking water to Kathmandu valley. It necessitates discharging at the end the regulated Langtang water into the Melamchi river instead of the Bhotekosi (Trisuli).
According to the Gandak Basin Master Plan a 120 m high dam has been proposed on the Langtang Khola near Jaithang. The volume of the reservoir would be about 180 million cubic meters. Based on revised concept the water in the reservoir at a full supply level of 3995 meters would be first tapped by the Langtang-1 power station operating at a gross head of 950 meters. The installed capacity of this Langtang-1 power station located near Ghore Tabela about 15 km downstream from the storage reservoir would be about 70 MW.
Water from the Langtang-1 power station would be directly drawn into the Langtang-2 power station. For augmenting this flow, the water from the catchment downstream of the storage dam would also be drawn into the headrace tunnel of the Langtang-2 power station. The installed capacity of the Langtang-2 power station operating at a head of about 1300 meters would be about 150 MW.
Why Langtang Power Would Be Very Cheap
Of all the site characteristics, head is the most important. Design guidelines, 1989 approved by the American Society of Civil Engineers has given some simple reasoning that would help to explain why the super high head Langtang power stations operating at many times greater head by comparision with other hydropowers could be built at very low cost. "Very simply if one doubles the head the quantity of water needed to produce a certain amount of energy is halved, Thus, for like site energy development the penstock area and reservoir volume are halved and further large cost reductions occur for powerhouse and machinery costs. This fundamental consideration is at the root of the large cost reductions that occur at higher heads."
A joint team of German, Japanese and US consultants has made an interesting reference to a Canadian high head project vis-à-vis the Upper Arun project to be operated at moderately high head. "It is worth mentioning that the search of the worldwide inventory of the existing hydropower installations identified only one plant with a combined head and flow magnitudes greater than that of the Upper Arun - Kemano in British Columbia, Canada". At present the electricity generated by the 896 MW Kemano Project with a 16.3 km long headrace tunnel operating at 800 m head provides power for Alcan's aluminum smelters at Kitimat at a cost below US cents 3 per KWh.
Power To Subsidize Water Supply
A Melamchi project conceived primarily as a power project linked with the existing Kulekhani hydropowers acutely suffering from water shortages along with the Langtang projects could provide Kathmandu people water almost for free A Melamchi project exclusively for water supply is obviously very expensive. The project involves the construction of a 28 kms long delivery tunnel. Thus, the Melamchi tunnel is too long. Apart from it, the tunnel size adopted based on the construction requirement is also very big for a scanty dry season flow of only about 1.5 cumec. The proposed tunnel could be used as a transit route for the passage of surplus Melamchi and Langtang waters into the Kulekhani storage reservoir acutely suffering from water shortage.
After the Langtang diversion the Melamchi tunnel could be expected to run in full capacity of about 15 cumecs throughout the year. It would permit a 35 MW Melamchi tunnel hydropower operating at a head of about 300 meters to generate annually about 300 GWh firm energy, which is 50% more than the generation of the both Kulekhani No-1 and No-2 hydropower stations put together.
Water Supply To Kulekhani
The electricity generation of the Kulekhani projects could be increased by 5 times if the combined flow of the Melamchi and the Langtang after setting aside adequate quantity of water for Kathmandu valley is delivered into the Kulekhani reservoir . It would be necessary to increase the capacity of the Kulekhani power stations . An additional 300 MW power station would be needed to utilize the 1000 meters head between the Kulekhani storage reservoir and the tailrace of the Kulekhani-2 near Bhainse.
New Ideas Should Be Explored
There is no denying the fact that countries all over world are at present engaged in fierce fights not in the battle field but in economic front and trying their utmost to find new ways to gain ground against their competitors. For this purpose even developing countries like ours are providing all out support to encourage and promote new research works in very complicated areas of science and technology
The possibility of developing the Langtang project for the generation of exceptionally cheap electricity on a big scale sufficient to meet our country's requirement for quite some time and also to supply drinking water to Katmandu valley for free should not remain a mystery to the institutions like the National Planning Commission, Academies or the ICIMOD. It hardly needs explanation that the institution like the ICIMOD is expected to rise above day to day office works to act as a think tank to reach out to member governments to sort out exceptionally vital problems confronting our region like the Kosi flood problem just in its own backyard. It could also help to develop awareness of the true value of the natural resources like the vast potential of the Langtang river that could be effectively utilized to gather rapid momentum in our efforts directed towards the socio-economic development of Nepal.
Langtang Projects Benefit/Cost
The total firm power generation of the proposed four power stations could be about 2500 GWh and their total capacity 550 MW. The projects could be developed in several stages. .All of them are very high head power stations. At such high head the unit construction cost could be only about US $ 1000 per KW capacity. The generation cost of the firm power could be slightly over US Cents 2 per KWh.
(Dr. Thapa writes on water resources)
