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LOCATION OF THE DAM

The Warsak Dam is located on the Kabul River in the province of NWFP, Pakistan, about 19 miles northwest of the city of Peshawar. The river rises in Afghanistan and provides drainage for the eastern part of that country. From Kabul, it flows eastwards through Jalalabad valley to the border between Afghanistan and Pakistan.

In Afghanistan, the River Kabul receives four large tributaries i.e. Logar, Panjshir, Alingar and Kunar. The catchment area of the river is about 26,000 sq. miles of which the Kunar valley alone contributes 9,500 sq. miles - most of which lies in Pakistan. The Kabul River falls into the mighty Indus near Attock, about 50 miles from Warsak dam.

ALTERNATIVE DAM SITES

Seven dam sites were considered for the siting of the dam. These were located 2-4 miles upstream of the Warsak head canal. Topographically, the most suitable sites for the dam were the three most upstream where the gorge was narrow and banks steep but these required larger amount of tunneling and the rock quality in this part was of inferior quality compared to the other sites downstream. The first site, the most downstream of the seven had best rock quality but a very wide gorge which would have increased the cost of the project immensely. Between the remaining three sites, one had poor geological conditions were not acceptable. Construction work started at dam site 2 in February 1949 but due to cracked rock findings the work was shifted to the 4th site from the head canal where rock quality was good and the gorge was not too wide.

PROJECT EXECUTION

The Warsak Multipurpose Dam was the first initiative of its kind after independence in Pakistan. The Government of Pakistan and the Government of Canada jointly executed the gigantic undertaking. The project took 5 years for completion through aid under the Colombo Plan by the Canadian government, setting a milestone of collaboration between the Commonwealth countries. The original estimated cost of the project by PC-1 in 1955 was Rs. 15.6 crores (Rs. 156 million).

Initially, the Government of Pakistan entrusted the then Central Engineering Authority (CEA) to carry out investigations for the project. Later, in December 1948, local consultants M/s Merz, Randell, Vetten (Pakistan) initiated investigations to estimate the cost. The Canadian consultants for construction were H.G. Acres and contractors were Angus Robertson Ltd. Pakistani counterparts were deputed from the CEA.

COMPONENTS OF THE DAM

The area termed as the Warsak dam site includes the main dam, stilling basin, powerhouse, power tunnel with penstocks and the diversion tunnel. All structures are located close to each other and the rock units are similar. Generally, the rock units may be divided into four categories (i) lower granite gneiss, (ii) multiple schist band, (iii) upper granite gneiss, and (iv) the phyllite - schist group.

The Warsak dam is a concrete, straight gravity type bulkhead. It is 460 feet high along the crest with a maximum height above the lowest bed rock foundation level of 220 feet. The spillway has been incorporated as an overall structure of the dam that consists of nine bays; each having high gates of 40 feet. Below the dam, a concrete stilling basin is provided to absorb and dissipate the energy of the falling floodwaters.

The powerhouse is located on the surface, on the right bank below the downstream face of the dam. A 35 feet internal diameter tunnel, which is 1,800 feet long with a maximum discharging capacity of 32,500 cusecs, is located along the left bank of the river extending from upstream to downstream face of cofferdam. Two cableway benches for concrete bucketing for the dam and stilling basin are also provided along the hill-slopes. The intake structure and power tunnel, having an internal diameter of 39 feet, are located on the right bank. There are 6 underground penstocks with 18 feet diameters for the 6 generators. A 3.5 miles long, 10 feet diameter concrete lined irrigation tunnel is located on the right bank to irrigate 120,000 acres of land.

CURRENT STATUS

There was no provision of silt exclusion in the design of Warsak dam, which resulted in silting up of the reservoir after three years of operation of the dam. Currently, the riverbed on the upstream side of Warsak dam has been raised to the extent that the dam is essentially run-of-the-river, with no capacity for storage.

Hydroelectric power is still produced but silting-up is a persistent problem for the power generators due to the inflow of coarse sediment. The Federal Government has allocated Rs. 77 million for the rehabilitation of Warsak Dam in 2001-02.

RECENT INTERVENTIONS

Since its commissioning in 1960, the condition of the power station has been deteriorating. This is mainly due to structural deformations, sedimentation problems and erosion in hydraulic equipment. The power station has been rehabilitated under a CIDA grant to restore its rated capacity and to enhance its operational life and reliability for 20-25 years.

At present, the overhauling of two units has been completed. As a result of this, the generation of power has increased. There was a 24.4 % increase in power generation in the year 2000 compared to the past year.

The Dams Safety Organization has been conducting annual inspections of Warsak Dam. This includes piezometric analysis and evaluation, collection of updated seepage and movement data of project structures. The findings and recommendations are issued bi-annually.

REFERENCES

1. Warsak Dam Organization, "Warsak Dam Multi-purpose Project - Completion Report".
2. Dr. Nazir Ahmed, "Water Resources of Pakistan"' Mirajuddin Press, Lahore, September 1993.
3. Pakistan Water and Power Development Authority, "Annual Report 1999-2000", 2001.
4. Pakistan Water & Power Development Authority, "Monthly Progress Report for February 2002", Hydroelectric Planning Organization, March 2002.