RAWALPINDI, April 26: While political wrangling over construction of large dams continues, about 3.50 million-acre feet (MAF) of water is lost as surface runoff annually in Barani (arid) areas. This magnitude of runoff has taken away the advantage of bringing green revolution in the rain-fed areas of Punjab.

Not only that, the runoff carries with it soil fertility and many dissolved pollutants, including plant nutrients, pesticides, and salts, reveals an official document obtained by Dawn.

This runoff is almost half of the reservoir capacity of Tarbela Dam, according to a government specialist on water resources. The dam, he said, had already lost almost 35 per cent of its storage capacity due to silt.

The occurrence of rainfall in Barani areas is highly erratic in terms of both space and time with most of the rainfall occurring during monsoon period from July to September. Due to uncertainty of rainfall, farmers normally minimize inputs to reduce the risk of loss in the event of drought and mainly depend on off-farm incomes for their sustenance, according to the document. However, in the context of crop production, arid lands have often been underestimated. More than 1,200 kilograms per acre of wheat has been produced in these areas under rain-fed conditions, which reveals a high potential for maximizing crop production, the report says.

The Punjab Government has constructed 35 small dams in the Potohar plateau since 1961, and these dams have brought only 0.1 million-acre feet of water under use. Small dams were designed to irrigate over 35,000 acres, but only 32 per cent of the anticipated command area has been developed, states the report.

Further, the average cropping intensity was also low being only 35 per cent against planned average of 96 per cent. On an average, 69 per cent water was being released from small dams, thus only 42 per cent of command area has been developed, the report says.

Due to high surface area to volume ratio, these small reservoirs are subject to high evaporation losses. On an average, small reservoirs lose 50 per cent of their impoundments to evaporation in arid and semi-arid zones. The seepage and percolation losses in small reservoirs are about 20 per cent of reservoir volume against five per cent in large dams, said the report.

Small dams in Potohar are also subject to high evaporation losses. On an average these dams lose about 20 per cent of their storage capacity and the cost of water is about Rs2,400 per acre-foot, according to the report.

Inadequate watershed management and natural and man-induced erosion of the fragile arid soil has also led to the depletion of soil and water resources, the report said. The high runoff in these areas is associated with the erosion and sediment transport and a huge amount of soil is being transported to these reservoirs. The vegetation growth in these dams indicates that top fertile soil from the catchment areas is being brought into these reservoirs, thus converting the productive land into non- productive, notes the report.