Pakistan since last five years (1997-2002) is passing through a cycle of draught and with reduced storage capacity of the two reservoirs the water crisis has reached its climax with no immediate solution in site. Kala Bagh Dam which could have been started right away is now more or less a dead proposal.

The other smaller dams being built not being on the national irrigation grid system, are of little help to alleviate or even minimize the water shortage being felt by the Pakistan’s Irrigation System with seventeen barrages and thousands of miles of canal network. The result is acute water shortage and water crisis waiting for the feasible solution which can be implemented immediately, since any further delay may end up in an environmental and economic disaster. This paper looks in depth and presents a possible solution to over come the crisis in immediate future.

2. Pakistan’s Water Budget: Figure 1 presents the water budget of Pakistan based on averages of last sixty yeas of flow data. The actual flows in the river may be much less than what is shown in the figure during the dry years and may be more in high rain fall years. However the deviation of high and low from this average affects mainly the discharge flowing into the sea i.e. 32 million acre ft. while the combined discharge of 101 maf diverted into the canals remain more or less constant.

However even this discharge into canals is now being affected because of reduced storage capacity due to silting of Tarbela and Mangla. The estimated water losses from seepage, in canals, in water courses and over irrigation are based on the average values as shown in the water budget of Pakistan (Figure1) and should not raise any controversy.

3. Categories of Losses: In general there are two main losses that occur during transportation and application of irrigation water. Nothing much can be done to check the evaporation losses except growing of trees along the canal banks which provide shade and thus reduce evaporation.

All the canals with few exceptions are unlined through which seepage is taking place amounting to 18.3 maf (includes Link Canals) per year. This loss is equivalent to almost two Tarbela reservoirs (gross capacity 7.5 maf after silting) and more than two Kalabagh reservoirs (max gross capacity 8.0 maf). The losses estimated in the water courses amount to 7.5 maf/year, which is equivalent to one Tarbela Reservoir.

The losses due to over irrigation amounts to 12.0 maf per year equivalent to 1.5 Kalabagh reservoirs, or more than 1.5 Tarbela reservoirs. Thus it will be seen the total seepage losses in the transportation and over irrigation totals to 4.5 times the reservoir capacity of Kalabagh dam. Add to this the water that can be saved by adopting drip irrigation system, wherever feasible on a country wide scale.

4. Over Irrigation: The irrigation method (i.e. method of applying water to the field) practised all over the country is “controlled flooding” in which water through a single source i.e. cut in the water course is allowed to flow down the field. Obviously areas close to the outlet recieve water much in excess than required by the crops while the areas at the end may not receive any water or receive less than required.

Therefore there is an uneven application of irrigation water causing wastage and this method of irrigation has lowest irrigation efficiency at almost 50% or less. This situation worsens further when our farmer indulges in over irrigation which causes further loss of irrigation water. The maximum water that should be applied at a time should not be more than the volume of voids in the root zone of a plant which in case of most crops is 3ft in depth. The plant utilize only 50% of this volume i.e upto the lower limit which is known as “field capacity level”(fig-2). If the root spread area for say wheat is taken as on the basis of 1ft spacing as 0.25 sqft and pore space for a typical agricultural soil of sandy silt at 10% of the total soil volume the maximum water holding capacity of the 3ft deep root zone would be 0.075 cft, equivalent to about 2.12 litres.

Therefore the maximum water that should be applied per sqft of soil at a time need not exceed 2.12 litre and any amount over and above this limit percolates down to the ground water below. The figure-2 explains the situation. In fact the water available and consumed by the plant is even less than the total pore volume, since the soil holds the water by surface tension only upto field capacity “which is normally 50% of the pore volume and rest of 50% water percolates down due to gravity and available to the plant for a very short period. (figure 2).

Therefore the water that should be applied at a time is the volume that would reach the “field capacity” level of the soil and amounts to 1.0 litre per sqft. Depending upon the size of the crop and evapo-transpiration rate this volume of water will be consumed in fifteen days. If an average is taken as 15 days than the water required for the crop would be 8.0 litres per season per crop sqft of the agricultural field in case of wheat.

The above calculations are based on two plants per sqft. In Sindh the delta of water for wheat crop is 6 inches and that of cotton is 8 inches. This amounts to 0.5 cft/sqft for the crop season which is equivalent to 14.16 liters/sft. This is on paper but actually the water applied to the land is much more than this volume, and varies between three to four times more than the above figure.

Therefore seepage from the agricultural field to ground water table for the Indus System estimated at 12 maf, per year is rather on conservative side, and this can be saved by adopting scientifically sound irrigation practices in controlled Flooding system of irrigation.

5. Saving Irrigation Water in Sindh: In addition to usual losses occurring in the unlined channels there is wastage due to wrong irrigation practices. A colossal waste of water is occurring due to “Pancho water” system in the cultivation of rice in Larkana, Shikarpur and other rice growing areas of Sindh. The duty of water in the area is as high as 15 cusecs/1000 acres a figure three to four times greater than as compared to other rice cultivation areas in Pakistan.

This is due to a misconception of the farmers that water should not stand for more than two days in the rice field else it looses its fertility, and capacity of cooling the soil. Result is gross wastage of this precious commodity and since there is no space to dispose off, the water flows down and collect in ponds along roads, railway and canal embankments, damaging the embankments, creating water logging and providing breeding facilities for the mosquitoes and spread of malaria. Another unfortunate situation which exists on the ground causing loss of water are the big land owners located on the upstream reaches of the minors or distributaries drawing by force and quite illegally as much water as they desire, which of course is in much excess of their requirements.

Unfortunately there is a common concept that more water you apply better is the crop. The land owner on the lower reaches suffer from the water shortages and uncertainties of supplies resulting in no cultivation and some times selling away their highly priced lands at cheap rate. This practice while causes waterlogging due to excess of water in the upstream reach it cause salinity due to shortage of irrigation water for the lower riparians. Sindh’s share of Indus water amount to 44.0 maf per year at the source.

Figure 3 below presents the scenario of losses in Sindh. Out of 44 maf the water that actually goes to produce the crops is 25.02 maf/year and seepage losses and loss due to over irrigation is 18.98 maf/year, equivalent to more than two Tarbela reservoirs. Then again if drip system is adopted for orchards, row crop and in other suitable situations, another 5.28 maf/year can be saved.

Thus with the elimination of seepage losses in distributaries, water courses, scientific use of water in control flooding method of irrigation, and than last but not the least use of drip system for orchards etc. will save 18.98 maf/year equivalent to building three Kalabaghs or more than two Tarbela reservoirs.

6. Proposed Measures: In general there are three major sections in which water can be conserved to overcome the crises.

*Extensive Lining Programm

*Minimize or Check

Over Irrigation

*Replacement of Flooding Method of Irrigation by Drip System.

6.1 Extensive Lining Programm:

i): Due to technical difficulties and on economical grounds it is not feasible to line major canals with more than 200 cusecs discharge. The canals including distributaries and minors ranging in discharge from 30 to 200 cusecs carry 39.6 maf/year having a seepage losses of 5.9 maf/year. There are 1100 such channels in Sindh with an average length of 15 canal miles. Total length amount to 16,500 canal miles. The cost of concrete lining with nominal reinforcements on an average basis comes out to be Rs. 4100/ft of canal length. The canal section varies, for a discharge ranging between 30 cusecs to 200 cusecs, with an average velocity of 1.6 to 1.9 ft/sec.

The total estimated cost for lining the distributaries and minors will amount to Rs. 64.5 billion, which would save 5.9 maf/year of water in Sindh alone. Similar calculation can be done for Punjab and NWFP. The live storage capacity of Kalabagh would be around 6.0 maf, thus only in Sindh the first part of the conservation program would amount to build one Kalabagh at a cost of 1.07 billion dollars, which is only 13.4% of the actual cost of Kalabagh, likely to be incurred at 2001 rates.

ii) The seepage loss of irrigation water through water courses amount to 3.4 maf year. The discharge in the water courses varies from 1 to 5 cusecs and there are 43000 water courses in Sindh. On the basis of an average length of a water course of one canal a mile, total length would be 43000 miles.

Out of this 2000 water courses have already been lined under IDA and World Bank farm management program. Based on an average discharge of 3 cusecs and an average velocity in lined section as 1 ft/sec, the average width of rectangular lined section comes out to he 2.0 ft and a depth of 1.5 ft. The cheapest linning would be that of fero-cement, however it is not recommended because it is likely to be damaged easily by animal crossing which is so common in rural areas, therefore “A” class burnt bricks as lining material is recommended which on an average costs about Rs 200 per foot length of the water course.. With an average length of a water course as one 1 canal mile, the total length to be lined becomes 41,000 canal miles.

This would cost about Rs. 41.0 billion (683 million dollars) and save 3.4 maf of water per year. In addition this would apply a check on the source of the water logging problem, and help reduce the discharge now being carried by the existing drains on the left and right banks of river Indus. The other major advantage is the job opportunities for the local villagers, in the massive linning program of water courses.

6.2 Controlling Over Irrigation: At present the irrigation method (i.e application of water to soil) in vogue is Controlled Flooding (CF) method in which water from one point source is allowed to flow down the field. This method demands perfect levelling of the field for maximum irrigation efficiency, and even at maximum efficiency it utilizes ten times more water than the drip system of irrigation.

However in Sindh and other parts of Pakistan there is an over irrigation which means even more water than what is needed in a Controlled flooding system. Three are three reasons, for excess application of water in this system i) The farmer’s wrong concept that more is the water better is the crop growth and produce. ii) In most cases the wara bandi system does not allow the freedom to apply water in right quantities at correct frequencies. The result is a colossal waste of 5.28 maf per year in Sindh alone. This water if saved will have two major benefits of; easing water crises and minimizing water logging and salinity. This can be achieved through a mass scale education of farmers, in the scientific use of water in the field. iii). In addition to over irrigation yet there is another major leak in the Sindh’s water budget. The Pancho water system used for the cultivation of rice in northern Sindh areas like Shikarpur, Larkana etc. is causing a colossal waste of irrigation water. General concept of a rice grower in these areas is that irrigation water if stands for more than a day or two in the rice field, looses its fertility and soil cooling capacity.

Therefore unlike the irrigation practice in other areas where water stands for weeks, here there is continuous inflow and outflow resulting in wastage of water. In this area the duty of canal water is as high as 15 cusecs per thousand acres as compared to the normal 3 to 3.5 cusecs/1000 acres elsewhere in the country. The over irrigation due to pancho water has raised the overall average duty of water to 7 cusecs/1000 acres (average value) as compared to 3.0 cusecs in Punjab and NWFP.

6.3 Drip system: Drip system can be introduced on a large scale in specific situations like orchards, row crops, and crops where plants are grown with spaces between them. The drip system utilizes about 10 % of the volume of water as compared to a maximum efficient C.F. system. It is quite complex to arrive at scientifically acceptable figure of the volume water that will be saved with the introduction of drip system and would need a detailed field study and data collection through field surveys for the orchards, row crops and source of water etc.

A collection research project should be taken up by the public or private sector agencies to arrive at a correct figure. In any case introduction of drip system would initiate a huge saving in the usage of irrigation water. 7.0 Conclusions. i) Lining of watercourses would save 12.0 maf per year for Pakistan (about 5.9 maf/year for Sindh).

This project can be taken up immediately and can be carried out, involving local population. This would not only save water but also provide jobs to the local /rural population. ii) Simultaneously the lining of canals less then 200 cusecs discharge can be initiated. iii) Awareness and farmer education program on scientific water usage should be launched on a mass scale. Volunteers trained in water usage should be sent all over the country equipped with knowledge, commitment, audio visual aids and films etc. Agriculture university students, agricultural extension service volunteers, irrigation department and NGOs have to participate to make it a success. iv) A task force should be created to develop this concept of National Water Conservation Programm (NWCP) into a reality, first on a small scale and then based on the experience gained, launch on all Pakistan or on provincial basis. v) Funding should be no problem if a clear concept is developed and benefits of saving water equivalent to four Tarbela size reservoirs made to appear a reality. Kalabagh dam alone is estimated to cost 8.0 billion dollars (i.e. about Rs.480 billion) while the total cost of lining canals, water courses check over irrigation and finally replacement of Flood Irrigation system with Drip system shall not exceed Rs. 480 billion. Already with the help of International Donor Agencies a Rs. 31.4 billion National Drainage Program (NDP) has been launched to provide surface and tubewell drainage, along with institutional reforms.

The proposed National Water Conservation Programm NWCP has a merit over NDP in that it applies a check at the very source of drainage water, i.e. channels and over irrigation. It is now known that NDP is only a partial success while NWCP holds a real promise to provide extra irrigation water, while aelequately covering NDP objectives. However, the proposal to conserve water in no case negate the idea of building more reservoirs on Indus, it is only complementary to the dam building program on Indus.

The cheap electricity and other benefits of building dams have no substitute.

References:

1.Dr. Iqbal Ali. Irrigation and Hydraulic Structures, Institute of Environmental Engineering & Research, NED University Karachi 1993.

2.Government of Pakistan “National Drainage Program PCI” Islamabad 1997.

3.Irrigation and Power Department, Government of Sindh “Canal/Minor Lining Including Cost Effectiveness “Note Personal and communication, Karachi 2000.

4.Sudhindra C., etal, “Tentative Recommendations for Ferro Cement Field Channels of one Cusecs Capacity”, Third International Conference on Ferro Cement, Roorkie 1988.

5.Chahisgaonker,R, Ferro cement Canal lining Indian concrete journal, Vol . 63, No. 6, June 1989.

6.Hillel , D. “Advances in Irrigation” Volume I Academic Press, New York London 1982.

7.Yaron B, Danfors, E and Vaadia, Y, “Arid Zone Irrigation”, Springler - Verlog, New York, Berlin 1973.