ISLAMABAD, June 23: The government has allowed the construction of the Tank Zam Dam in the NWFP at a cost of Rs4.6 billion to generate 25MW and irrigate 45,000 acres annually.

Sources told Dawn on Thursday that the project had been approved to help the province substantially increase its agricultural productivity, which would contribute to alleviating poverty.

According to the water and power ministry, it will be a 260ft high earth filled dam envisaged to impound the flood waters of the Tank district and achieve a storage of 30,000 acre-feet. The embankment will have a length of 1,250ft at crest elevation of 2,282 feet and shall span about 450ft at end level with a crest width of 35ft.

Drainage through the embankment will be guided by chimney drain connected with a horizontal drain in the downstream portion of the dam.

The drainage basin at its entry into the Dear Is mail Khan plain measures 840 square miles. The length of the watercourse is 60 miles from Waziristan mountains to its confluence. The main confluence is Shahur, with a drainage area measuring 360 square miles.

The headwaters of the river drain the Razmak mountains, which reach an altitude of 11,000ft. The upstream portion of the drainage basis is covered by vegetation and forests, which are being exploited.

The river valley is narrow, with some modest enlargements here and there. The river bed is still covered and the valley consists of conglomerates, sandstone, lime stone, clay stone and other rocks.

Of a total area of 102,049 acres, 39,248 acres are under cultivation. The project aims at providing water to 45,000 acres in Tank.

It was said that plains of Gomal basin had been encountering the flood hazard of five hill torrents, the major ones being Gomal Zam and Tank Zam, threatening life and property in the area and eroding about 3,000 acres annually.

Tank Zam, after flowing through a wide valley, enters into a narrow gorge at Hinis Tangi and attracts the construction of an earth-filled dam involving moderate quantities.

The construction of a 260ft high earthen dam at the proposed site would ensure a usable storage of 237,300 care feet acre-feet, which will cater to the considerably varying flow of Tank Zam in a particular year or cycles of years, besides accommodating the silt charge of the stream and this would give an acceptable life to the project.