How to Plan Dams on silty rivers like the Indus for longer life

In the legends of the rivers, the Indus River is Pakistan’s Aab-i-Hayat. The Indus River perhaps is the most highly silt carrying river in the world. Its water enriches the soil. It is the second largest river in the world after River Nile. For building dams on silty rivers like the Indus, reservoirs rapidly lose storage capacity due to silting. Therefore, great care be taken for the selection of dam site to have long life. Dr Pieter Lieft nick report “Water and Power Resources of West Pakistan, Volume I, 1968, page 251 reports “Any plan for the construction of reservoirs in Pakistan must consider the problem of sedimentation, particularly true for the reservoirs, on the Indus. This is because the rate of sedimentation is such that a profound effect on the life of the Indus reservoir will be made”. The report further says, “Tarbela Dam site may be taken as an example of high sediment load, its reservoir will be fully depleted in about 50 years”.

“The major drawback of Tarbela Reservoir is that the useful life of the reservoir will be rather short on the order of 50 years because of rapid sedimentation”. Page 245. For replenishment of storage lost due to silting, further large-scale capacity will be needed to meet the growing irrigation needs and to help capacity lost by siltation of Tarbela”. Page 242. It has now been observed that Tarbela Reservoir has lost storage due to silting by (11.6-6.6) = 5.0 maf in 36 years. The second dam to be built on the Indus will be after 36+8=44 years.

Dr Pieter report further reveals, “Extremely little is known about the silt load of the Indus –its origin, time of occurrence, nature etc  and very little work has been devoted to trying find a solution; obviously the problem is becoming very important for it will gradually eliminate much of the value of a multi-billion dollars” Page 136.

“Therefore, a thorough survey of the silt problem and of its means to overcome it is urgently needed”. Page 137. “Therefore there is urgent need to start investigation of siltation problem”. Page 234. The above are some excerpts from Dr Pieter Lieftnick report.

I have revealed the source of silt and one of the most effective solutions to stop silt flow in the Indus or reduce it to the minimum.  

In a country like Pakistan that depends on canal irrigation for agriculture to produce food, there is dire need for long life storage dams, as dams are the basic and the most vital input to supply water to crops as per crop consumptive use as and when required in proper dozes. Dams are part of irrigation system for the timely availability of water for crops. Almost silt free water, released by dams would run the sprinkler and Drip system of irrigation efficiently.  

The Indus is the only river in Pakistan where few mega dam sites are available for creating storage reservoirs. Unfortunately, every dam site on the downstream of Katzarah is less attractive than the one on its upstream. Therefore, storage dams on the Indus be selected on priority basis that have longer life. This is very necessary because there are no dam sites on  big rivers of Pakistan, the Kabul River, the Jehlum River and the Chenab River. We depend only on the silty Indus. Therefore, we must plan a dam on the Indus that has the best capacity inflow ratio for longer life span. Besides this, extensive watershed management measures be taken to reduce land erosion and silt flow.

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The example of Hoover Dam or Boulder Dam on Colorado River in USA is quoted. The life span at the time of construction of Hoover Dam was 100 years. After carrying out watershed management in the catchment area, the life span, of the dam now is about 1000 years.

Watershed Management

Watershed Management is a vital pre-requisite to stop silt flow and increase the life of reservoirs. Watershed Management is carried out in the catchment area of storage dams before and after the construction of dams. It is a continued process till silt erosion and silt movement is almost stopped. Watershed Management is done by building check dams/bunds all over the catchment area, by growing forests and greenery to check soil erosion and reduce the speed of rainwater runoff to slow down the velocity flow and silt movement.

The building of storage dams on the upstream of the river will reduce silt flow for all the storage reservoirs on the downstream. This is because, the storage dams on the upstream work as watershed management measure for the downstream storage dams. For example, the existence of Tarbela on the upstream will reduce the sediment inflow to Kalabagh being on the downstream. Tarbela would serve as watershed management infrastructure for Kalabagh Dam. Similarly, Basha Dam will serve as watershed management infrastructure for Tarbela Dam. Basha Dam on the upstream, on completion, would increase the life of Tarbela Dam. Katzarah Dam if built will increase the estimated life of 90 years of Basha Dam to about 800 years. 

The Indus originates in Tibet at a height of 18000 feet. It begins its long journey from Singikabad spring. Therefore, watershed management in its most upper mountainous reaches is not possible. Watershed management activities shall therefore, be confined to Pakistan. 

The most vital measure to increase the life span of reservoirs is to select dam site on a river where the Capacity-inflow Ratio of a site is the best. Select a dam site on all rivers where the reservoir storage capacity is larger than the annual river flow at that site. This will create more space for silt deposition and give longer life. This is one of the best solution to stop silt flow, on the downstream. As such, the 35 maf Katzarah Dam is the solution to the silt problem.

Pakistan is most unfortunate to select storage dam site at the tail end of the Indus valley at Kalabagh where sediment load from the Indus is the highest. Kalabagh has the poorest Capacity inflow ratio on the Indus, as its storage capacity is 6.1 maf against the river inflow of about 93 maf. The CI ratio comes to (0.06). The inflow is 15 times more than the storage capacity. It draws silt from a huge catchment area of 110500 squire miles. The reservoir will silt rapidly. It will have a very short life span.

 The annual sediment load at Kalabagh site is 540 million tons that comes to about 0.3 maf each year. This means the storage at Kalabagh will be lost in about 20 years. Dam site in the upper reaches has better Capacity inflow ratio and longer life span. Katzarah Dam site has the best capacity inflow ratio in the entire reach of the Indus River. Katzarah storage capacity is 35 maf where as the river inflow varies between 27 maf to 35 maf. Gomal Dam site at Khajuri Katch discovered by me in 1959 has excellent capacity inflow ratio. The reservoir is many times larger than its annual flow. It will have long life though Gomal River is very silty.

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 Dams are built in USA at sites on rivers that have several times more storage capacities than the river inflow at the dam site. This gives longer life span. Please see table below;

                                    Table showing Capacity inflow Ratio

            Name of       Name of      Storage             Average         Capacity

            Reservoir      River           capacity of       annual            inflow

                                                      Reservoir          run-off           ratio “I”

                                                      In maf “C”        in maf “I”                                                           

            Garrion         Missouri          23.0                17.6                 1.8

           

  Elephant Butt          Rio Grando      2.6                  1.1                    2.4

   Rockland                 Neches              6.9                 1.7                   4.0

   Ford Peck                Missouri            19.4                4.2                   4.6

   Dennison                  Red River          5.5                  4.14                 1.33

   Boulder                     Colorado            34.0                15.0                2.26

   Khajuri Katch           Gomal                 2.7                  0.5                  5.4

  Tarbela                  Indus                    11.6                   67.0                  .017

  Kalabagh               Indus                     6.1                     93                    .06

  Katzarah                Indus                     35.0                   27.0                  1.3

The above chart shows that reservoirs in Pakistan have poor capacity inflow ratio, specially on the Indus River. Therefore, we must be very careful in selecting dam sites from life point of view. The planner should know that the upper dam functions as watershed management structure for the lower dam. In view this, we must start building dams from the upstream of the river so that downstream dams have get longer life span. This arrangement will serve as Water shed Management infrastructures. These conditions are not necessary for a dam built on run-of-the-river for the single purpose of hydropower generation, like Munda Dam.

Pakistan has not realized that its economy and prosperity is based on irrigated agriculture and on the construction of multipurpose dams to store water for agriculture and produce cheap hydropower. Even then, it has created hardly 9% storage of its total runoff from rivers. This is calamitous. Agriculture requires water in time and in proper dozes. Crops require ensured water from storage dams in time. In conditions like in Pakistan, storage dams be created to store at least 40% of the annual runoff if not more. Absence of storage dams for 36 years made Pakistan victim of scarcity of water and crippling load shedding. It also made victim of rapid silting. Besides this, it made Pakistan victim of Inter-provincial Water dispute

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and the victim of the Indus Waters Treaty for the rapid silting of Tarbela dam by 6.6 maf. All this is very alarming.

Silt study on the Indus

It is unknown to many that in late sixtees, Dr Attaullah Former Principle of Engineering collage, Peshawar conducted silt studies on the Indus under the World Bank programme and the Planning Commission of Pakistan. Dr Attaullah findings are that the “source of silt” is the vast Skardu valley as the soil of Skardu valley is one of the highest erodible soil in the world. The Indus River flow carry heavy sediment load from the Skardu valley. Dams on the Indus River in tail reaches will rapidly silted up and shortened the life of reservoirs.

 The best and effective remedy to control silt flow in the Indus River is to submerge the erosive silty Skardu valley by building a high dam at Katzarah having 35 maf storage capacity so that silt flow is stopped and stays in the valley. This is the only remedy to reduce silt flow in the Indus and increase the life of storage dams. Otherwise, all dams built on the Indus will rapidly silt up one after the other. As such, Pakistan will lose all dam sites on the Indus due to rapid silting in 100 years. The irrigation system will then be on run-of-the-river.  

Building Katzarah is the “save Pakistan” project to sustain irrigated agriculture in the Indus basin specially when India has usurped Pakistan share of water from Chenab, Jehlum and Indus Rivers. Dam building should start from the upstream. Basha Dam will prolong the life of Tarbela by 40-50 years and Katzarah will prolong the life of Basha Dam from its 80-90 years estimated life, to 800 years. Tarbela and Kalabagh, both are wrong choice for selecting dams in lower reaches of the Indus. They have the lowest priority. Tarbela would have 5 times more life span if built after Katzarah and Basha. This is what proper planning means.

Rapid silting of dams is an extremely serious matter for the Indus basin irrigation system. Irrigation system to supply timely water to crops depends on long life storage dams to produce optimum food.

The selection of dam site has therefore great bearing on the silting of reservoirs and the Life of the dam, its usefulness for sustained irrigated agriculture to produce food for the rapidly growing population. Silting is destructive for the life of reservoirs and for agricultural development. The death of the reservoir starts the day it is built.

 I advise the Government of Water and Power to select dam sites on merits so that it has long life span. I advise, a priority list of dam sites be prepared, keeping in view the CI ratio. Dams on the upstream increase the life of dams on the downstream. This arrangement, if practiced will make a useless dam site on the downstream, useful.  Capacity inflow ratio must be given the highest priority, it should never be ignored. Presently, dam sites are selected wrongly, without caring for CI ratio with short life span.

Kalabagh and Tarbela Dam on the Indus were selected at random in the lower reach. They have short life span due to rapid silting. Such sites become controversial besides technically doubtful. Kalabagh remained controversial for the past 36 years. This, as a result, caused water shortage and crippling load shedding besides delaying the second dam to be built on the Indus for 36=8+ = 44 years. Locating dams at whims or easy approach to site, ignoring

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long life of the dam, is wrong. This practice must stop in national interest. I believe, load shedding will continue till Katzarah and Basha Dams are built.

I earnestly urge to create Indus Valley Authority (IVA) to plan, and build dams on the Indus wherever feasible, using the entire fall of the Indus River from its extreme head in Pakistan to the tail end of the Indus River valley like the Indian did in occupied Kashmir on Chenab, Jehlum and the Indus River. The Indians are now planning to do the same on Kabul River for Afghanistan. The IVA will also do the same for the Indus River and its tributaries of Swat River, Panjkora River and Chitral River. A 450 high dam may be built on Chitral River at Mirkhani to divert part of its floodwater (4 maf out of 10 maf of the Chitral River annual flow) to the Panjkora River valley through 20 mile long tunnel to be stored in the 8.5 maf Shigo Katch Reservoir of Guroh Dop Dam on Panjkora River.

I urge an early Water Treaty with Afghanistan. Khalid Aziz former Chief Secretary NWFP prepared a detailed report on Kabul River for Water Treaty with Afghanistan two and a half years ago. The report contained maps, charts, all relevant data, including water data. He submitted the report to all concerned. Khalid Aziz also prepared the inter-provincial Water Accord 1991 intelligently, and made all the fighting parties to agree. A difficult task pending for years was achieved miraculously. He substantially contributed to the settlement of NFC award.