March 17, 2006

By DR. AB THAPA

For many of us closely following the activities related to Nepal ’s water resources development in general and the hydropower generation expansion in particular, the present severe power shortage crisis has not come as a complete surprise. Everybody knew that the NEA would be forced in very near future to resort to load shedding. The nature of present load shedding does indicate that the NEA is now experiencing shortage of both capacity (KW) as well as energy (KWh).

The power shortage crisis is going to deepen further in the years to come because the demand for electricity in our national grid with a total firm capacity of about 500 MW is expected to grow steadily at an annual rate of about 5 to 7 percent. Except for the 70 MW Middle Marshyangdi Project, other major new power projects are nowhere near which would have come into operation within the next 5 to 7 years. Thus we are now being dragged into a whirlpool of deep power shortage crisis.

Power Supply from India

At present the NEA appears to be pinning its hope on import of electricity from India to meet our demand for electricity in dry seasons. It might not be a good solution because India itself is experiencing power shortage. Moreover, if we look into the Power System Study Report of the Karnali (Chisapani) Project, it is found that there is a big variation in seasonal demand pattern in Northern India . By comparison with the monsoon season period the demand for both capacity as well as energy exceeds by about 25% and 10% respectively during the winter months of the dry season. Thus, it clearly shows that India could not be a reliable supplier of electricity particularly during the winter dry seasons when we experience an acute power shortage.

Natural Gas from Bangladesh

It is also said in some quarters that the NEA should import natural gas from Bangladesh to generate electricity to meet the growing demand for power in our country in the near future. Such proposition could be considered outright unfeasible due to the following reasons.

Natural gas occupies 600 times more volume as a gas than as a liquid, as a result, it is not feasible to transport natural gas in a container. Natural gas turns into a liquid at -160° C It can be stored and shipped as a liquid at that temperature. Liquefied natural gas is transported primarily by ship. Despite the fact that the natural gas can be transported by ships in liquefied form, it is far more economical to transport the natural gas through pipeline. Thus the possibility of using the natural gas to generate electricity in our country to meet our growing power demand is virtually ruled out. We can neither think of using ships to transport liquefied natural gas from Bangladesh to Nepal nor to use pipeline for this purpose in near future.

A New Solution

Needless to explain that we should give the topmost priority to works to expedite the completion of the construction works of the 70 MW Middle Marshyangdi Project to shorten the period of the present acute power shortage. Perhaps a special panel composed of the representatives from the relevant ministries, National Planning Commission and the NEA should be constituted to resolve all outstanding issues that could delay the completion of the project. We should try, if possible, to bring into operation at least one generating unit well ahead of the final commissioning of the project.

There is an easy way to soften the impact of the present power shortage crisis if we launched the program on a war footing to utilize the full potential of the existing Kulekhani storage reservoir and hydropower stations ( Kulekhani 1 & 2 hydropower) to generate extra power by diverting from Kathmandu valley the surplus flow of the Bagmati river into the Kulekhani storage reservoir. Initially it would be only the Bagmati flow but later on after the diversion into the Kathmandu valley the Melamchi water could also be added into the Kulekhani reservoir.

The Kulekhani Reservoir and Power Stations

It is reported almost every year in local newspapers that the electricity generation of the Kulekhani hydropower stations is going to be reduced by a substantial margin because the Kulekhani storage reservoir is half-empty at the end of the monsoon season, with the result that the NEA would be forced to resort to load shedding in the coming dry season. This problem would certainly be solved if the surplus water from the rivers in the Kathmandu valley is pumped into the Kulekhani reservoir to be stored for the supply to the Kulekhani hydropower stations in the dry season.

The Kulekhani reservoir operation rule for the Kulekhani-1 with an installed capacity of 60MW is framed by a basic discharge pattern of 6.2 cum./sec. in the dry season from December to March and 2.1 cum./sec. in the wet season from April to November. The former is designed to generate four-hour peak power using the maximum discharge of 13.1 cum./sec. and 20-hour base load using 4.8 cum./sec. The latter is to utilize 6.55 cum./sec. for the peak power and 1.21 cum./sec. for the base load respectively.

Available water for the Kujlekhani-2 power station with an installed capacity of 32 MW is comprised of the outflow from the Kulekhani-1 and the runoff of the Mandu river. The firm discharge of the latter with 90% dependability at the intake is estimated to be 0.2 cum./sec. both in winter and summer. Thus the maximum Kulekhani-2 discharge is designed to be 13.3 cum./sec.

Diversion from Kathmandu to Kulekhani

The Bagmati river water in surplus to the need in the Kathmandu valley could be diverted into the Kulekhani reservoir from a place near Chobhar gorge. Mean flow of the Bagmati river at Chobhar is quite abundant during the monsoon seasons. Even in the winter months of the dry season starting from December to the end of March when the demand for the electricity in Nepal is very high the average flow of the Bagmati is expected to be about 2 cum./sec. The half empty space of the Kulekhani storage reservoir ( with an effective storage capacity of 73.3 million cubic meters) could be utilized to accommodate about 20 million cubic meters monsoon season flow of the Bagmati river. Thus the Kulekhani hydropower could be provided throughout the 4 winter months additional 4 cum./sec. flow. Out of this total flow, the water drawn directly from the Bagmati would be about 2 cum./sec. and the stored Bagmati water would provide the remaining 2 cum./sec.

The diversion of the surplus Bagmati water from Kathmandu valley to the Kulekhani reservoir could be a very simple and at the same time the most cost effective proposition despite the fact that at first glance it might appear to be a somewhat complicated engineering task. Let us consider that we are going to draw about 4 cum./sec. Bagmati. water from somewhere near Chobar. The total power generation of the Kulekhani 1& 2 hydropower plants would almost be doubled by investing only about US $ 20 million in the construction of the proposed diversion structures including the provision of a pumping station.

The Proposed Plan

We might have to build a 15 MW pump station at Chobar to lift 4 cum./sec water to a height of about 300 meters which might be equivalent in height to the full supply level (FSL) of the Kulekhani storage reservoir. It is equally possible that instead of one big pump station we might need two or more small pump stations with a total capacity of about 15 MW if the topography does not allow to provide a single stage pumping. A 15 km long waterway might be needed to carry the water into the Kulekhani storage reservoir out of it the length of the tunnel could be about 9 kilometers. The total cost of such diversion is estimated to be roughly about US $ 20 million.

The construction of the proposed Bagmati diversion works could be completed within 2 years with one additional year for the initial preparatory works. The NEA might not require external foreign investment. It could mobilize its own resources to finance this project.

Melamchi Water into Kulekhani Reservoir

After the completion of the proposed Melamchi river diversion into the Kathmandu valley there would be a substantial increase in flow of the Bagmati river at Chobar. As a result, the electricity generation of the Kulekhani 1&2 hydropower stations would be further increased.

The cost of the delivery tunnel from Melamchi to Kathmandu valley according to the Bankable Feasibility Report prepared by the British firm Binnie&Parteners under the UNDP assistance is only about US $ 50 million at 1995 price level. The design of the proposed Kulekhani 3 Hydropower should also be reviewed and perhaps its capacity might have to be raised to about 150 MW to meet the steadily growing peak load demand if it is decided to divert the surplus Bagmati water into the Kulekhani reservoir. There is also a possibility of diverting the regulated flow of the Langtang river into the Kulekhani reservoir if such regulated flow is utilized to generate electricity by using the high elevation difference between the Langtang river and the Melamchi. The diversion of the Langtang into the Kulekhani reservoir could provide more than enough electricity to meet our country’s growing demand for power over the coming decade.

Langtang-Melamchi-Bagmati-Kulekhani Interconnection

The proposed Langtang-Melamchi-Bagmati-Kulekhani interconnection would help to unfold the prospect for developing hydropower stations in a cascade with a total hydraulic head of over three kilometers that would allow to generate electricity at a cost perhaps the lowest in our region. The proposed interconnection plan comprising of several virtually independent projects can be developed at several stages, as a result, the full implementation of the entire scheme could be spread over a long period.

The hydropower generation potential of the Langtang river is quite high because it is possible to provide a fairly large storage reservoir at a very high elevation in the upper reach of this river. The Langtang storage reservoir can be operated to provide all through the year an uniform flow of about 15 cumecs in the middle and lower reaches of Langtang-Melamchi-Bagmati- Kulekhani grid. A total head of about 3500 meters could be utilized for power generation by 5 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.

Why is Langtang Power 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 comparison with other hydropower plants 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."

In Conclusion

The proposed Bagmati diversion could be implemented within a very short period to meet the growing demand for power in our national grid. The proposed diversion is going to be perhaps the most economic project because we do not need to invest on construction of the reservoir, power stations and transmission lines. We are going to utilize the existing power stations, reservoir and other structures. For pumping surplus monsoon period water from the Bagmati river into the Kulekhani reservoir we can use the seasonal energy generated by our run-of-the-river hydropower projects. At present such seasonal energy is almost entirely wasted.

The proposed Bagmati diversion could be looked upon as a part of the big plan to utilize the full potential of the Langtang- Melamchi-Bagmati-Kulekhani interconnection to generate cheap power on a scale sufficient to meet our country’s need for power for over the next decade.