LAHORE -  Only 20 mcm (Million Cubic Meters) of water is currently being harvested out of a total potential of 375 mcm, with functioning just around 600 ‘tobas’ out of 1,600 ‘tobas,’ while thousands have lost their storage capacity due to sedimentation.

These views were expressed by the experts at a seminar on ‘Water crisis in Cholistan’ organised by Pakistan Engineering Congress here at PEC. Among other speakers, the seminar was also addressed by PEC President Engineer Chaudhry Ghulam Hussain.

The key speaker Dr Muhammad Akram Kahlown, in his lecture titled ‘Rainwater harvesting in Cholistan Desert’, observed that more harvesting and long-term storage of rainfall will be needed to help the herdsmen and their flocks reduce migration to avoid such droughts, as a major potential for additional water harvesting exists in the Cholistan desert.

The speaker said that the Cholistan desert is spread over an area of 2.6 million hectares. This vast area provides fodder to 2 million livestock. However, the carrying capacity of present rangelands has been seriously reduced due to droughts and over grazing. The situation demands proper range management to ensure sustainable supplies of fodder to the livestock. Field trials conducted with sprinkler irrigation with one or two applications of water have improved vegetation cover. The water used in the sprinkler had 3,000 parts per million Total Dissolved Solids. Such innovations need to be expanded to improve vegetation cover in the rangelands. Quick-growing fodder species grown on saline water need to be planted and grown where possible.

To overcome the problem of drinking water supply in the Cholistan, the PCRWR has constructed slow sand filtration plants on selected reservoirs in the Cholistan desert, he added. He said the problem with rainwater harvested and stored in the ‘tobas’ is the turbidity and microbiological contamination, adding that these problems can be overcome by using slow sand filters developed by the PCRWR.

He said that the ‘tobas’ with sufficiently large potential water watersheds could be replaced by the 15,000 cubic meter reservoirs designed and constructed at 92 sites by the PCRWR and constructed at 61 additional sites by the CDA. “Smaller reservoirs will be needed for ‘tobas’ which have smaller watersheds. These smaller tobas help disperse the flocks and avoid overgrazing that otherwise occurs near the large reservoirs. However, the ability of these small tobas to continue to water flocks during long dry seasons is limited because of their shallow depths. Deeper small tobas are needed,” he added.

Dr Akram said that the rising cost of fuel argue for trial and evaluation of less expensive types of excavation, such as exploding ammonium nitrate placed in bores at the desired sites. “The bottom of the resulting pits will probably be difficult to seal and substantial seepage may occur. But where does it go? It will probably build lenses of relatively low salinity water that floats on the more dense saline water, somewhat subject to mixing with the underlying saline water, but not subject to evaporation, which is the primary dissipater of water from surface reservoirs in deserts. These lenses could be a vital source of water for drinking during droughts, similar to the fresh water lenses still available in and near the bed of the old Hakra River, which ceased flowing and contributing to the groundwater many centuries ago.”

To identify locations where relatively fresh water can be exploited, a resistivity survey was carried out which resulted in identification of 20 locations, he said and added that 20 tubewells were designed and installed in the Cholistan desert at identified locations to provide dependable alternate source of water.

He said that the combined potential supply of water from these 20 wells is about 14 million cubic meter per year, enough to meet most of the water requirements of the present desert human and livestock population.

Dr Akram said that saline groundwater in the Cholistan desert is available in abundant quantity. The salinity range monitored in the desert varies from 400 to 20,000 ppm. Groundwater is available at shallow depths in the most of the desert. These factors are essential conditions for using reverse osmosis membrane technology to lower the salt content from water to levels which are acceptable for drinking and household uses, he added.

The PCRWR has installed one desalinisation plant at the Dingarh Research Station, capable of treating 50,000 liters per day. The increasing cost of diesel fuel and the availability of large amounts of solar energy and heat in the desert argue strongly for research to find ways for using solar and thermal energy, with reverse osmosis membranes, to obtain drinkable water from the deserts saline ground-waters.

In his presentation, Dr Akram suggested that the local population can be motivated to grow fish using the reservoirs excavated in the Cholistan desert for rainwater storage. He pointed out that fruit tree plantation activities carried out at Dingarh field station of the PCRWR have shown great potential.

He said that migration from the Cholistan can be reduced by arranging water for the human and livestock populations and developing other associated facilities including good rangelands, healthcare and education.