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Water resource development potential By Dr Sardar Riaz A. Khan

Documents: 

Population of Pakistan has risen from 32.4 million in mid 1948 to 144.5 million in 2003, and is estimated to increase to 168 million by 2010, and to 221 million by 2025.

This uncontrolled increase sounds alarm bells for policy makers because it will enormously increase water requirements for food and fibre, industrial and domestic uses. The existing use of water in agriculture is 93 per cent, industry three per cent, and in household four per cent.

Pakistan's agriculture depends heavily on man-made irrigation system with over 90 per cent of production coming from 18 million hectares of total irrigated area. In view of the increasing demand for water in the coming years there is a need to study water resource development potential and stock of the resources' inventory.

Surface water: The country's primary water resource is the River Indus and its tributaries. Under the Indus Water Treaty of 1960, the flow of three eastern rivers of Satluj, Beas and Ravi (26 MAF) was conceded to India.

Pakistan is now dependent on three western Rivers Indus (including Kabul), Jhelum and Chenab. On the basis of 81 years' data (1922-2003), the average annual inflows of western rivers at rim stations are 138.4 MAF, while the average annual inflows at the rim stations during post Tarbela (1976-2003) were 140.8 MAF. About 16 per cent of the annual river flows in Rabi (winter) and 84 per cent in Kharif (summer) seasons.

The original live storage capacity of 15.37 MAF of Mangla, Tarbela and Chasma dams on the Indus River System has declined by 4.68 MAF by 2003, and may further drop by six MAF by 2010 suggesting the need of new large, medium and small dams.

The government has initiated the construction of small and medium dams and various canal projects. Their completion will increase the water availability by 12.6 MAF. Nevertheless, the total availability of future development is 25 MAF after deducting Indian uses, Kotri outflow to check the sea intrusion, and possible uses of Kabul River by Afghanistan.

The sub-group water resource development in the Tenth Five-Year Plan estimated that the irrigation water availability at Moga (outlet) is 78 MAF out of 105 MAF of water diverted into the canal system.

As such 27 MAF is lost in the secondary level irrigation system attributable to surface evaporation seepage from the unlined canals and the poorly maintained canal banks. Lining of canal distributaries and minors can save this colossal loss.

The major loss of 49 MAF occurs at tertiary/watercourses level due to the poorly-designed and maintained watercourses, poor land-levelling and defective irrigation practices at the farmers' field. This loss can be checked by renovation and lining of the watercourses and precision land-levelling.

According to the Director General On-Farm Water Management Punjab, who is also a member of the a fore mentioned sub-group, implementation of these recommendations at secondary and tertiary levels will save 50 per cent of the total water loss of 76MAF, saving 38 MAF to meet the increasing needs of agriculture.

Groundwater: It supplies over 40 per cent of crop water and permits greater demand-based timely irrigation of crops in and outside the Indus Basin. It has been reported that the total groundwater potential is 55 MAF and currently 49 MAF is being exploited.

According to the recent Wapda report, the sustainable groundwater is 64 MAF, of which 42 MAF is presently used and the gross useable potential is 26 MAF (64-42 multiplied by 1.2 times re-circulation of the pumped water).

Of these 20 MAF is not useable and only six MAF is the sustainable groundwater potential. Similar studies showed that out of 7,00,000 tubewells currently installed in the country, nearly 70 per cent pump out slightly to highly brackish water.

Use of well-established sulfurous acid generator technology has great potential to make this brackish water useable for crop production on gypsiferous soils, while the use of gypsum technology for making it useable on non-gypsiferous soils.

The low and medium salinity water can be conjunctively used with the canal water by the ratio of 1:1 and 5:1 depending on the salinity and sodicity. If canal water is not available then the aforementioned technologies can also be used in such areas.

Nevertheless, these technologies have the potential of making 20 MAF of non-useable water useable. Again, the well established saline agriculture can be followed by using the non-useable saline water, especially in our 10.6 million hectares of sandy deserts Sandy desert soils provide excellent strata for quick percolation of water through sand.

The salt tolerant plants growing on sandy soils are well aerated as sand affords more space between its particles. The chlorides of sodium and magnesium, the components of harmful saline water are easily washed down to deeper layers of sandy soils without affecting the selective root system of plants.

The harmful sodium ions are not absorbed on sand particles unlike their easy absorption on the surface of clay particles. Use of chemical components further improves the prospects of saline agriculture as is being successfully followed in several countries of the world including India, Australia, and the US.

RAIN WATER: It has been reported in draft report of the concerned sub-group on the Tenth Five Year Plain that the potential of rain water is 3MAF. This is not correct. The estimated average annual rainfall in the country is 180 MAF while 50 per cent of which is lost as the run-off.

Even if this loss is taken at 20 per cent, the average annual run-off loss comes to 36 MAF. The existing conventional water harvesting practices in our arid and semi-arid regions comprising 88 per cent of the total geographic area of the country, hardly collects up to 25 per cent of the precipitation, while modern water harvesting technology enables to collects up to 90 per cent of it thus significantly increasing the crop yields.

The lowest limit of water harvesting is 50-80 mm of rainfall. In Pakistan rainfall varies from less than 100 mm to over 1000 mm with an average rainfall of 400 mm suggesting a good potential of rain water harvesting. Around 10 mm of rain equals to 1000 litres of water per hectare.

Rain water harvesting provides water for regions where other sources are, too distant. The modern rain-water harvesting technologies are now followed in several countries of the world, most of which are getting their rain-fed crop yields nearly equal to irrigated yields.

Of the various rain water harvesting techniques roof-top water harvesting from residential, commercial and industrial buildings is being successfully followed in several countries of the world to meet the declining groundwater availability for domestic and industrial purposes as rain water is the only alternative.

This system has been made mandatory in many Indian cities. Even, the annual requirements of the Indian President's Palace are met from its roof-top rain water harvesting.

The Indian government had earmarked Rs450 million in their Ninth Five Year Plan for this purpose and has given directives to the State and the Municipal Bodies to undertake roof-top rain water harvesting, its collection and recycling for domestic purposes and using it for recharging groundwater mandatory.

In Pakistan, roof-top harvesting has not been even included in its Tenth Five Year Plan. Cities like Karachi, Lahore, Rawapindi, Islamabad are facing serious water shortages, but there is no plan of utilizing fresh roof-top water harvesting.

Instead water from Khanpur Dam has been diverted to the twin cities of Islamabad and Rawalpindi to meet their domestic requirements which could be used for agricultural purposes. Similarly, sewage water could be collected, treated and recycled to meet domestic requirements as is being successfully done in other countries such as England, China etc.

Again there is unlimited potential of using sea water along our 1,050km long coast for domestic, industrial and agricultural purposes after desalinization it as is being now done in over 125 centres in the world.

The draft report by the Water Sector Sub-group reckons that the total future water development potential is 34 MAF - surface water 25 MAF, groundwater six MAF, rainwater three MAF as against the increased water requirement of 37 MAF by 2025.

This prospective drought-like condition can be considerably overcome 1) by remodelling, renovation and lining of our canal irrigation system both at the secondary and tertiary levels, and laser land-levelling as it alone will save 38 MAF of water.

2) By making 20 MAF of saline groundwater useable by following the modern techniques.

3) There is potential of harvesting 36 MAF of rain water.

4) Restricting groundwater off-take to 70 per cent of the annual recharge rate will check over-mining of groundwater and its exhaustion, especially in Balochistan where exhaustion has become a serious problem.

5) Following the water resource conservation agriculture may further save irrigation water between 20-40 per cent.

6) Changing to drip irrigation system may reduce water requirements from 40-60 per cent.

7) Sprinkler irrigation on undulating lands may further save water.

8) Encouraging crops with low water requirement will save water.

9) Sea water resource should be utilized by desalinization to meet the anticipated increased industrial, domestic and agricultural requirements from Gwadar to Karachi after the completion of the national highway along the Sea coast.

10) Techniques may be developed towards imparting greater permanency to structural interventions and effective management of hill torrents as most of the hill torrent water is going waste.

The projected future water resource development potential of 34 MAF is a questionable figure. The actual water resource development potential is far greater to meet the present drought-like situation which is mostly due to mismanagement and poor planning for utilizing the existing water resource potential.