NEW REVELATIONS COULD BE EMBARASSING:
Upper Tama Kosi Hydropower Project
By Dr. AB Thapa
On one hand the Nepal Electricity Authority (NEA) is pinning all its hope on early implementation of the Upper Tama- Kosi Hydropower (UTH) project to resolve the present load shedding problem, and on the other hand that hydropower project is yet to be thoroughly studied to make certain that it is worth implementing that project in foreseeable future. The UTH project is surrounded by many doubts about the completeness of the study to justify taking the decision to implement that project. It appears based on previous studies that the proposed Upper Tama-Kosi project apart from being a project entangled in serious technical problems would be found to be at a great danger of being totally washed away by glacier lake outburst floods(GLOF) much the same way as happened to the Namche Bazaar hydropower some times back
There are significant differences between the findings of the JICA study of the Upper Tama Kosi conducted under the Kosi Master Plan study and the present study of the Upper Tama-Kosi project carried out by the NEA with foreign assistance. The JICA study was extensive and tried to cover fully the whole Tama-Kosi basin. The NEA’s highly positive findings of the Upper Tama-Kosi project would make sense if the Japanese experts conducting the Tama-Kosi basin would have gone wrong.
It is very important to know about the accuracy of the cost estimate before making a final comment in favour or against any project. Unfortunately the bitter past experience of blindly believing in the manipulated cost estimate of the Khimti Hydropower is still fresh in the minds of Nepalese people. An unacceptable level of inaccuracy in cost estimate of the 60 MW Khimti Hydropower project had forced our country to buy electricity from the private developer based on a very high US $ 140 million revised cost of that project though the original cost of the project based on the feasibility study carried out by the NORPOWER just before the commencement of the construction was only US $ 60 million. Now it has become crystal clear that the NEA’s present financial crisis resulting in repeated hiking of the electricity tariff is the direct consequence of its inability to verify the accuracy of cost estimate and few other simple technical matters of the Khimti and other hydropower projects implemented by private developers.
Schemes on the Tama- Kosi River
The Tama- Kosi River is the second largest tributary of the Sun - Kosi River . The downstream courses will be submerged by the planned Sun-Kosi No.2 reservoir. Therefore, JICA team conducted the study of the river courses further upstream of the Khimte Khola confluence for hydroelectric power generation. Originally 6 hydropower stations in a cascade were planned. The Tama-Kosi No.1 was later eliminated because this stretch of the Tama-Kosi was found to be within the Sun-Kosi project storage reservoir based on the optimization study of the latter.
The Tama-Kosi No.6 according to the Kosi basin Master Plan is the uppermost project. The intake of this project is located just upstream of the confluence of the Rolwalling Khola and the Tama-Kosi. The intake of the proposed Upper Tama-Kosi Project is said to be further to the north close to the China-Nepal border. It is believed that the JICA team had deliberately overlooked the uppermost stretch of the Tama-Kosi. The team might have felt that the uppermost reach is hazardous for hydropower development. It could be for reasons of danger of GLOF. This reach of the Tama-Kosi is very close to places in Nepal and Tibet where very dangerous glacier lakes are located. Thus, any GLOF incidence would have left in its wake the most horrific destruction on this stretch of the Tama-Kosi.
Daily Storage Reservoir
The installed capacity of the proposed Upper Tama-Kosi Project is said to be over 300 MW. It is said that the proposed Upper Tama-Kosi project hydropower would be provided with a storage reservoir to supply water to meet the daily peaking demand for electric energy. In the absence of such daily storage reservoir the firm capacity of the proposed Upper Tama-Kosi project might have been only about 100 MW despite the fact that the installed capacity is over 300 MW.
The bed slope of the Upper Tama-Kosi is expected to be extremely steep. A very high dam is needed to provide a daily storage reservoir adequate in volume. JICA study under the Kosi Basin Master Plan had ruled out the possibility to provide daily storage pond to serve Tama-Kosi-5 and Tama-Kosi-6 projects. We have learnt from our past Arun-3 Project planning experience that the provision of a daily storage reservoir by damming the river course itself in case of the rivers like the Arun or Tama-Kosi is going to be extremely difficult task that would certainly involve a huge investment. In case of the Arun-3 Hydropower Project, it was planned that a dam only 20 meters in height would suffice to provide daily storage pond but at the final stage we had to raise the height to 65 meters.
Study of Glacier Lakes Dangerous For Nepal
At present glaciers are retreating in the Himalayan region, as a result, glaciers lakes are being formed. Such ephemeral lakes disrupt communication systems and various infrastructures like hydropower directly, or indirectly subjecting the mainstream to periodic catastrophic floods. Glacier lake outburst floods also produce peaks in sediment transfer.
In 1988 a joint team of Sino-Nepalese conducted the studies of the glaciers and glacier lakes in the Arun and the Sun-Kosi basins primarily in the Tibetan region of China. The Lanzhou Institute of Glaciology and Geocryology took part in the study from the Chinese side, similarly the Water and Energy Commission took part from the Nepalese side.
According to the findings of the above mentioned joint study, there are many glacier lakes in Arun, Tama Kosi, Bhote-Kosi, Trisuli, Buri Gandaki and Karnali basins within Xizang ( Tibet) of China which have some past records of the glacier lake outburst floods (GLOF) events. Sino-Nepal joint study carried out in 1988 had extensively covered only the Bhote-Kosi (Sun-Kosi) and the Arun rivers. The joint study report has recommended to conduct similar extensive studies to cover Tama Kosi and other basins also.
In 1990s Dr. Tomomi Yamada of Japan and Dr. B.P. Upadhyay, Professor of TU were involved in the study of glacier lakes within Nepal The study was conducted under the Water and Energy Commission. Their study covered Lower Barun , Chamlang Tsho, Naulekh, Sabai Tsho, Dudh Kund, Mojang, Tsho Rolpa, Duwo, Thulagi, Khyimjung and Kang Guru glacier lakes.
The glacier lakes study conducted jointly by experts from the JICA (Japan International Cooperation Agency) and WECS in 1991 provides detailed description of the Tsho Rolpa glacier lake on the end of the Trambau Glacier within Nepal in Tama -Kosi basin. The lake makes contact with the cliff-shaped glacier end, and it is covered with thick debris. This lake is extremely dangerous. The lake can be seen in a photograph presented in the report.
Glacier Lakes Outburst History
On August 4 th 1985 the nearly completed Namche hydropower plant was completely destroyed by the Dig Tsho glacier lake outburst flood( GLOF). The Dig Tsho glacier was on the terminus of the Langmoche Glacier. The GLOF damaged not only the entire Namche Hydropower station but also all the bridges, trails, cultivation fields, houses, livestock along its path to the confluence of the Dudh-Kosi and the Sun-Kosi rivers at a distance of 90 km from the Dig Tsho glacier.
Since the nineteen forties, according to Sino-Nepal study, there have been at least 10 cases of glacier lake outbursts within the basins investigated. Among them there have been five bursts in three glacier lakes of the Arun River Basin , and four in three glacier lakes of the Sunkosi River (Bhote-Kosi) basin.
In Arun basin the most common are the end moraine-dammed lakes. Because the end moraine-dammed lakes mostly consist of end moraines formed in the Little Ice Age and are closer to their source glaciers, or connect directly with the glaciers, changes in the glaciers directly influence the water level of the glacier lake and the stability of the dam. At the same time, owing to the fact that the end moraine dams are composed of new and loose till, they are uncompacted and therefore unstable. This type of glacier lakes are easy to burst and cause floods and debris flows. The end moraine-dammed lakes are distributed most at the source of several short and small tributaries in the left side of the Arun River . They are distributed over a transitional zone from maritime to continental glaciers.
Gelhaipuco is an end moraine dammed lake located in the headwaters of Gelhaipu Gully ( Natangqu River Basin , east of Riwo, Dinggye County ). At 14.00 on Sept. 21, 1964, the lake burst abruptly. According to the study of the Chinese Academy of Sciences, there was a heavy precipitation in the Nantangqu River Basin , which caused the glacier of the Natangqu River to slide. Huge amount of ice slid into the lake. The generated shock waves triggered the lake water to overflow the moraine dam causing the burst. There was a breach across the dam which was 30 m deep. The debris flow rushed down to the lower reaches of the Arun River in Nepal , and caused heavy economic losses
At mid-night, July 11, 1981, an end moraine dammed lake located at the headwater of the Sunkosi River suddenly burst. A breach of 50m deep and 40-60m of bottom width was formed at the moraine dam. The highest burst discharge was about 1600 cu. m./ s, which was observed 23 minutes after the burst. The high flood lasted about 60 minutes and the burst water amount was estimated at 19 million cu. m. The debris flow damaged the Kodari Highway and the Sun-Kosi Power Station in Nepal . The flood destroyed the Friendship Bridge at Kodari. According to the investigation of 1984, there had been a similar burst in 1964 from that same lake, but the burst discharge and damage caused was smaller.
In Conclusion
It is hoped that our Government would not take a decision in haste to implement the Upper Tama-Kosi project without thoroughly establishing that the project is technically sound and economically feasible.
(Dr. Thapa writes on water resources)
