This article has been written in response to an article titled "Unfeasibility of the Kalabagh Dam", by Engr. Fateh Ullah Khan, published in daily Dawn on November, 1, 2004.

The Kalabagh Dam (Project (KDP) has been in the national focus for the last several years. Never in the past has a project generated such an intense debate on such a wide-scale. This is indicative of the importance of the project which would be the largest public work in Pakistan's history, and one of the largest multi-purpose dams in the world.

The dam is to be built on the Indus river at a distance Of about 16 miles upstream of Jinnah Barrage and 92 miles downstream of Attock, the confluence point of Kabul and Indus rivers. The dam will control one of the world's great catchments, spread over 110,000 square miles in area.

The project includes construction of 260 ft. high dam which will create a reservoir with usable storage of 6.1 million acre feet (MAF) for multipurpose utilization of power generation, irrigation supplies and flood control.

The project has two spillways, on the right bank for disposal of flood water, in the event of the highest probable flood. These spillways will have a discharge capacity of a little over 2 million cusecs.

On the left bank will be the power house connected to 12 tunnel conduits each 36 ft., with an ultimate generation capacity of 3600 MW. Sediment sluicing: The effects of drawing down the reservoir were studied by examining three basic modes of sluicing; nominal, mid-level and low-level. These modes are explained below;

If the reservoir were operated to provide the greatest economic return, it would be drawn down to below El 850 by early May in most years, and the level would reach El 825 and remain there for an average of about 20 days before the refilling period in July.

El 825 is the lowest assumed reservoir level for power generation. The effect of this annual draw down would be to rescuer sediment deposited in the upper reaches and carry it towards the dam.

At the same higher velocities generated by the draw down would help to pass (flush) incoming sediment through the reservoir without deposition. The sluicing of sediment resulting from this mode of operation is termed "nominal sluicing".

If the optimum economic operation is modified slightly the reservoir can be deliberately drawn down to the minimum generating level of El 825 in June and held there for up to 50 days.

This mode of operation is specially beneficial in wet years when sediment transport conditions are particularly favourable. This mode of operation is called "mid-level sluicing". The reservoir level would be held at El 825 from the start of June to the 20th July each year.

The early studies considered special low level sluices to achieve very low draw-down. However the great disadvantage of such "low level sluicing" is that power generation must be discontinued and thus the economic penalty is large.

With the existing design the reservoir could be drawn down below El 825 by using convertible conduits 11 & 12. This could help in occasional scouring of deposits just upstream of the dam, should such flexibility be required. However occasional sluicing at levels lower than El 825 is unlikely to significantly influence the overall sedimentation pattern in the reservoir.

Comparison of the three modes showed that low level sluicing was very uneconomic and did not give a significant advantage in sedimentation. However mid-level sluicing showed significant advantages in retaining reservoir live storage compared with the nominal sluicing. Thus further refined studies were based on the concept of mid level sluicing.1.1 Mid-Level-Sluicing

With the mid-level sluicing the reservoir will be drawn down to El 825 each year by the end of May. In years other than dry years this draw-down will be achieved partly by cutting back on release from Tarbela in April and May, and as a result increasing the generating head available there subsequently, and, particularly in wet years, partly by releasing more water from kalabagh than is needed for irrigation.

The additional releases from kalabagh will be used to generate as much power as possible to offset the reduction in power from Tarbela resulting from the cut-back in its releases.

From the start of June, Kalabagh reservoir will be held at El 825 by releasing water through the turbines and the orifice spilway. The reservoir operation and economic studies have assumed a sluicing period of 50 days each year but this could be adjusted from year to year in the light of experience and the circumstances pertaining at the time.

At the end of the sluicing period, releases from the reservoir will be restricted to those required for irrigation or power so as to ensure that the reservoir will normally be refilled before the end of the high flow season.

The adoption of sluicing at El. 825 for a fifty-day period from the beginning of June as part of the project operation has the effect of greatly reducing the rate of depletion of the Kalabagh live storage. After 50 years 4.4 MAF of the initial life storage of 6.1 MAF will still be available and even assuming no further upstream storages, it is estimated that 3.2 MAF will be available after 100 years of operation.

Besides greatly increasing the life of the reservoir, sluicing will limit the build up of deposits in the upper end of the reservoir and thus help to ensure that there is no deterioration in the flood risk in the upstream areas.

In the article referred to at the beginning, no data, no calculations, or references to any technically valid study have been given while rejecting the "mid-level sluicing". On the other hand, Wapda has carried out exhaustive studies, used the latest computer modeling techniques and obtained the advice of highly reputed international experts.

On what grounds, the writer of the article claims that the "mid- level sluicing" will be defective and incapable to evacuate silt out of the reservoir, while the physical and mathematical models speak otherwise.

STUDIES: It was in 1953 that Kalabagh was identified as a potential dam site for storage as well as power generation. In the last 50 years, the Kalabagh dam project has been subjected to comprehensive and exhaustive engineering studies and explorations. Its feasibility has been confirmed by several independent consulting firms, of international standing, at various times (Table-1).

During the project preparation, the World Bank, and Wapda reviewed various reports (Table-2), in connection with the feasibility of the project. These reports were generally used during the preparation of the project proposal.

Experts from different countries of the world reviewed the design of the Kalabagh Dam Project (Table-3). The project was conceived as a result of extensive studies carried out by international consortium of consultants. International and the local experts reviewed the work of the Consultants and has confirmed the technical soundness of the project.

A panel of distinguished Pakistani engineers have reviewed the project plans. An eminent Chinese specialist reviewed the sedimentation studies, and those relating to flood levels in Kabul Valley.

An independent panel was also constituted in late 1987 to review the refined studies of sedimentation's particularly its effects on flood levels at Nowshera. All these experts and engineers have endorsed the project plan as technically sound and economically viable.

The KDP is a highly complex gigantic multipurpose engineering project involving investment of billions of rupees. No one or two engineers, no matter how qualified and brilliant, could pass absolute judgment on its various technical aspects.

Backwater effect of Kalabagh lake (El 915) would end about 10 miles downstream of Nowshera. The state-of-art computer based study, backed by physical modelling, has established that recurrence of record flood of 1929 would not affect the water level at Nowshera even after 100 years of sedimentation in reservoir.

The computer study, did not include the effect of Tarbela reservoir which is now factually providing relief by attenuating flood peaks. These studies were reviewed by Chinese expert (Dr. Lianzhen) and later by an international panel of experts (POE) headed by Dr. Kennedy of USA who was nominated by the government of NWFP. Both reviews are highly supportive of the studies. The POE has stated in their report that the results of this study are conservative.

Backwater effect of total culturable affected land under the reservoir is only 35,000 acres. Cultivable and to be submerged under the reservoir elevation of 915, and acquired permanently, would be 27,500 acres (24,500 acres in Punjab 3,000 acres in NWFP.

Of this irritated land would be only 3000 acres (2,900 acres in Punjab and 100 acres in NWFP). The balance 7500 acres is the land that will be temporarily submerged by floods with recurrence interval of 1 in 5 years.

Apprehensions expressed from time to time regarding the project have been thoroughly examined with the help of elaborate technical studies, Which have revealed that most of these are based either on lack of information or hearsay. Studies have proved that the Kalabagh dam from all angles is a sound technical project.

HIGH BARRAGE: Barrages are gated structures having low crests and are constructed across rivers for directing flows to canals at a constant water level. There is no canal diversion envisaged from Kalabagh reservoir and if a constant water level is maintained at the barrage pond it will be filled up with sediments rapidly. The storage capacity of the barrage pond will be too small to effectively regulate river flows.

The capacity inflow ratio (CIR) of a reservoir depends upon the topography of the site and is not the only criteria for planning a technically feasible and economically viable multipurpose project. The CIR of the KBD Project is 0.069 per cent. As stated above the life span of the Kalabagh reservoir is considerable because of the effective sluicing regime of reservoir operation.

It must be relished that for the KDP extensive investigations have been carried out and that the highest quality of engineering knowledge and expertise available at the international level, have been applied to the planning and design of the project.

POWER GENERATION: During the months of high water flows from June to September, hydro power (MW) depends on the reservoir levels which will be rising as refilling occurs. When the reservoir is full (RL 915), Kalabagh's initial eight units will be able to generate 2776 MW.

With large amounts of energy generated during the summer months, the station will operate as a source of base load power. During the other months of the year, water releases will be limited to meet irrigation demands, so less energy will be restricted to peak time operation.

Kalabagh will generate an average of 11,413 million Kwh annually giving a plant capacity factor of 54 per cent for the initial installed capacity of 2400 MW. The conjunctive operation of Kalabagh and Tarbela will enable Tarbela to generate 336 million Kwh of electricity in addition to its existing power production. The conjunctive operation of the two reservoirs will also enables up to 600 MW of additional peak power to be generated at Tarbela.

The proportions of thermal and hydro power and energy generated in Pakistan vary throughout the year. Hydro generation is chosen when possible in order to reduce fuel costs, but its availability is dependent upon seasonal variations in reservoir levels, river flows and irrigation release requirements.

The high and low output from a dam is a normal phenomena and for planning purposes the lowest possible generation during some events either when it is being emptied for some emergency reasons or due to lower demand is not normally taken for design purposes.

The availability of power from Kalabagh especially with the two dams being operated in conjunction is much greater than is usually available if there was only one reservoir. The inclusion of Kalabagh in the system is expected to improve the situation at Tarbela as well which will generate an additional 336 million Kwh at Tarbela.

There is no such concept to put 1000 MW for thermal generation provided in the project. Whenever any multipurpose project having power as an integral part is designed, it is normally matched with the future generation expansion programme of the country.

Following this concept when Kalabagh was designed it indicated that even with the 2400 MW available still there would be shortages of power which shall be met either by constructing another hydel project in the country or by thermal generation if the generation expansion programme was to be met with.

It was for this purpose that since there was no hydel power project in the offing, at least 1000 MW thermal power was suggested to be provided in the power system of the country. It never meant that this thermal generation would be placed at Kalabagh dam to meet any shortage during the low production periods at Kalabagh.

SEDIMENTATION: Kalabagh reservoir will extend for 92 miles up the Indus from the dam site and 36 miles up the Soan river, and about 10 mile sup the Kabul river from the Kabul-Indus confluence. At its maximum level of 915, the reservoir area would be 164 square miles.

The average annual flow at Kalabagh is 89 MAF of which 72 per cent comes from Indus, 25% from Kabul and 3% from Soan and other local tributaries. The 6.1 MAF storage of Kalabagh reservoir will be only 7 per cent of the average annual flow.

All reservoirs, sited on sediment carrying rivers, have an estimated life span for the length of time which they can meet their designed functions; Mangla and Tarbela reservoirs are no exception. However, this is not the case for Kalabagh reservoir.

Some features of Kalabagh reservoir are very favourable for sluicing of sediment. Firstly, the Orifice spillway of Kalabagh Dam has its crest elevation 40 ft. below the minimum level of 825 SPD.

Secondly, the operational rules specify the retention of the reservoir at the minimum level of 825 SPD in the months of June and up to 20th July, which shall enable direct sluicing of the silt laden early floods, as well as the removal of the sediment deposited in the preceding months.

Thirdly, the long and narrow gorge type reservoir favours flushing of the reservoir by high flows during the flood season. These features allow considerable less sedimentation in the reservoir and in effect, give a perpetual life to Kalabagh reservoir.

These conclusions are based on a very extensive study, using the latest engineering? techniques. Experts of International standing have verified and confirmed these conclusions.

The technical and economical feasibility of Kalabagh Dam Project (KBDP) has been established beyond any doubt. World renowned experts have reviewed the engineering studies of KBDP and found such studies of high engineering standard.

The cost of the project which is based on detailed engineering studies is very reasonable when compared to other similar projects. The project is ready for implementation.