DEEP CUT IN POWER SUPPLY
AB Thapa
The NEA has started to extend further the load-shedding hours. Now we are having six hours of load-shedding each day. Local newspaper “Kantipur” has reported that the NEA was forced to take such a drastic measure because the Kulekhani reservoir, which is the only storage reservoir in the country that can provide regulated flood season water to generate electricity during the dry season, is almost empty. Such a decision of the NEA to introduce deep power cut has certainly been received with a great dismay by everybody.
The newspaper “ Kantipur” has provided information on firm capacity of the Kali-Gandaki, Marshyangdi and Trisuli hydropower also which, however, does not appear to be correct. All these hydropower stations have daily storage reservoir to regulate water that enables them to operate at full capacity even in the driest months during the peak load hours. In other words the hydropower stations Kali-Gandaki or Marshyangdi would be able to generate 144 MW or 69 MW respectively during the peak load hours (contrary to what has been reported that they can generate only 80 MW and 30 MW respectively). It, however, looks certain that the power shortage crisis is going to last until the onset of the coming monsoon season unless there will be dramatic change in rainfall pattern.
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 at least 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 due to our shortsighted planning.
Softening the Impact of Power Shortage Crisis
There is an easy way to soften the impact of the power shortage crisis if we launched a programme on 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 and later on the Melamchi river into the Kulekhani reservoir. The design of the proposed Kulekhani 3 Hydropower should also be reviewed and perhaps its capacity might have to be raised to over 100 MW to meet the steadily growing peak load demand if it is decided to divert the Bagmati water into the Kulekhani reservoir. .
Full Use of Kulekhani Reservoir Capacity
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 oncoming dry season. This problem would certainly be solved if the surplus water from the Bagmati river 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 power station 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 maximum Kulekhani-2 discharge is designed to be 13.3 cum./sec.
Diversion of Bagmati into 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 over 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 Bagmati water stored in the Kulekhani reservoir 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. It is explained hereinafter that 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 a pumping station.
The Proposed Design
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 several 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 could be 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.
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.
Rationale Behind the Bagmati Diversion
The proposed Bagmati diversion could be implemented within a very short period to meet the ever 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 seasonal energy generated by our run-of-the-river hydropower projects. At present the seasonal energy is almost entirely wasted. The proposed diversion plan would open a route to transfer Langtang River water via Melamchi tunnel into the Kulekhani reservoir for generation of exceptionally cheap electricity.
Langtang River Potential
According to the Gandak Basin Master Plan study carried under the UNDP assistance, a fairly large storage reservoir can be provided in the uppermost reach of the Langtang River and thus the hydropower development potential of this river is quite high. . The Langtang storage reservoir can help to provide all through the year an uniform flow of about 15 cumecs in the middle and lower reaches if this river is developed in combination with the Melamchi Project.. There would be a total head of about 2500 meters between the full supply level of the Langtang storage reservoir and the Melamchi powerhouse tailrace that would be discharging the Melamchi and the Langtang waters into the Kathmandu valley. Such an enormous head could be utilized for power generation by 3 hydropower stations to be built in a cascade and out of them two power stations would be operating at an exceptionally high head of about 1000 meters or more. The surplus Langtang and Melamchi waters after the use in Kathmandu valley could be easily delivered into the existing Kulekhani storage reservoir and, as a result, it would be possible to run in full capacity the Kulekhani No-1 & No-2 hydropower stations by almost tripling their present annual power generation capacity.
The Langtang Power Projects
The Langtang projects operating at a head of about one thousand meters and more could produce electric energy at a very low cost . Apart from it, water in abundant quantity could be supplied to the Kathmandu valley for free. The concept of the Langtang project solely for power generation was developed under the UNDP supported Gandak Basin Master Plan study . However, this concept required some revision to incorporate the drinking water supply component to provide water to Kathmandu valley. It necessitated that at the end the regulated Langtang water after power generation be discharged 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 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 stations could be built at a 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."
