IRRIGATED agriculture is the backbone of Pakistan’s economy. The agriculture sector is the major user of water and its consumption will continue to dominate water requirements.

Direct rainfall contributes less than 15 per cent of the water supplied to crops. The major user of water for irrigation is the Indus Basin Irrigation System. About 106 million acre feet (MAF) out of 157 maf of surface water is being diverted annually for irrigation while around 48 maf is pumped from groundwater.

With large cultivable land base of 77 million acres (MAs) of which only 36 MAs are canal commanded, Pakistan still has the additional potential of bringing about 22.5 MAs of virgin land under irrigation.

With increasing population, Pakistan is fast heading towards a situation of water shortage. Per capita surface water availability was 5650 cubic meters in 1951, which reduced to 1400 in 2000. The minimum water requirement to avoid being a “water short country” is 1,000 cubic meters. In the year 2012, Pakistan will have reached the stage of “ acute water shortage”.

As part of the Indus Basin Replacement Works, two major dams, 5 barrages and 8 link canals were constructed to alleviate the problem. However, due to excessive sediment inflows in the river water, all the three storages (Tarbela, Mangla, Chashma) are rapidly losing their capacities. By the year 2010 these storages would lose 34 per cent (5.83 maf) of their capacity (See Table), which virtually means loss of one mega storage project. The present storage capacity is only 11 per cent of the total surface water and there is a potential for development of 65 MAF of storages, whereas about 38 maf of water escapes annually into sea. To save and utilize the available water, construction of additional storage facilities is essential for sustainable irrigated agriculture which supports about 70 per cent of the population of Pakistan which is largely poor.

National demand for electricity has been and would keep on growing rapidly. Development of hydropower has not kept pace with the demand. As a result hydropower potential of the country has largely remained unutilized.

In view of this situation, WAPDA has planned a Water Resources Development Programme,”Vision:2025” to meet water and power demand, with the short term, medium term and long term strategy — short-term plan from year 2001 to 2006 (Phase-I), medium term plan from year 2006 to 2011 (Phase-II) and long term plan from year 2011 onwards (Phase-III). This programme on implementation would provide additional storage and hydel power to the system, which is urgently required to cope with food and energy requirements of the increasing population and to ultimately achieve sustained economic development. Raising of Mangla Dam is a major component of Phase-I.

Mangla is the only site on Jhelum river where a dam with large storage capacity could be built. On this site construction of Mangla Dam was completed in 1967 as part of the Indus Basin Treaty replacement works. At the time of its construction Mangla Dam was the largest dam of its type in the World. Since its completion, the dam has performed very satisfactorily conserving excess summer flows for irrigation releases in winter. Generation of hydropower has been another major benefit from the project.

Main features of the project include four earth dams with a maximum height of 454 ft. (138 m) and a total length of about 8 miles (13 km). For flood routing, two spillways are provided. Hydropower is generated through ten units of 100 MW each. Water to the power generating units is supplied through five tunnels. Irrigation releases are usually made through the tunnels, occasionally supplemented by release through the main spillway.

When completed Mangla reservoir had a gross storage capacity of 5.88 MAF, which by now has reduced to 4.68 MAF. The capacity will reduce to 4.50 maf by the time the dam raising is completed in 2007.

Since its completion in 1967, the gross storage capacity of Mangla reservoir has reduced by about 20 per cent due to sediments deposition. Compensating for the capacity lost to sedimentation was in mind and a provision for raising of the dam was kept in the original design and construction of the dam. Raising of the dam has now gained importance on account of the ever increasing shortage of irrigation water due to sedimentation of the country’s two major storage reservoirs at Tarbela and Mangla. Mangla Dam is now being raised by 30 ft. to regain the reservoir capacity lost to sediment deposition and make provision for future sedimentation.President Pervez Musharraf performed the ground breaking ceremony of the project on September 30.

The major components of the works comprise raising of the dams and main spillway headworks and construction of a control weir upstream of the emergency spillway. All the ten power generating units were designed for raised Mangla conditions. Therefore, additional energy will be produced without making any alterations or additions in these units.

The project will augment supply of irrigation water at a time when the country is in its dire need. There will be additional power generation and further flood alleviation. On the average, annual water availability for irrigation releases would increase by 2.9 maf. The average annual output ofthe power plant is estimated to increase by about 180 mw. The raising project will generate major construction activity and employment opportunities.

The dam has already contributed significantly towards improvement of the environment in terms of agriculture growth, job opportunities and improved standard of living. Availability of additional water and hydropower will further enhance these positive impacts.

At the time of original construction of Mangla Dam, land on the periphery of the reservoir was acquired upto El. 1210 ft. For the raised Mangla reservoir, additional land, measuring 15,780 acres, will be acquired. About 78 per cent of the land acquisition will be in AJK and the remaining in Punjab. By raising of the dam about 44,000 persons will be displaced and about 8000 houses will be affected.

For resettlement of the displaced population a new city adjacent to Mirpur has been planned.The new city will be developed as a garden city with modern infrastructure and public amenities. In addition, four small towns will also be developed on periphery of the reservoir for affected persons who would choose to resettle near to their original habitat. Infrastructure of the new city and the towns will be developed at the project cost.

The writer is a Member (Water), Wapda.