Pakistan's water resources: -- problems and remedies.
Soon after independence on April 1, 1948, India unilaterally stopped the water supplies to Central Ban Doab Canal (CBDC) and Dipalpur Canal, claiming her sovereign right over the water passing through its territory. The control of the headworks regulating flows to these canals was with India. The border line between the two countries was drawn in disregard to the irrigation supplies. This water conflict, however, was settled through good offices of the World Bank in the form of Indus Water Treaty. As a result of this treaty, India was given the right to make exclusive use of the three eastern rivers (Ravi, Sutlej and Beas) with an average annual flow of about 43 million acre-feet (MAF. Under this treaty, Pakistan got the right to make full use of the three western rivers (Indus, Jhelum and Chenab) with an average annual flow of about 140 MAF. Also, the World Bank provided assistance to Pakistan to augment its irrigation supplies by diverting water from the western rivers to the eastern rivers so that areas af fected by this treaty can be irrigated. Under this agreement, two reservoirs (Mangla and Tarbela), eight link canals (Trimmu-Sidhnai, Sidhnai-Mailsi, Mailsi-Bahawal, Rasul-Qadarabad, Qadarabad-Balloki, Ballok-Suleimanki, Balloki, Balloki-Suleimanki, Taunsa-Panjna, Chashma-Jhelum), and six diversion barrages (Chasma, Rasul. Qadirabad, Marala, Sidhnai, Mailsi Syphon) were constructed to provide alternative sources of water to feed the eastern canals affected by this treaty.
After construction of Tarbela reservoir in 1974, no single reservoir has been added to the Indus Basin Irrigation system so far, while India and Turkey built 24 and 65 dams respectively during the same time period to meet the food, and fibre demands of their growing population. The population of Pakistan has crossed the limit of 140 million in year 2000 and will be doubled in 2025 with its present alarming growth rate of 2.8 per cent. More than 70 per cent of the country's population is engaged directly or indirectly in the agriculture sector. Agriculture is considered the backbone of Pakistan's economy and its sustainable production depends on the irrigation water availability. Pakistan is facing acute shortage of water supplies and water availability per capita has reduced from 5300 cubic meter in 1951 to 1200 cubic meter in 2000 against the international standard of 1500 cubic meter. Moreover, flows in the Indus river to the Arabian sea after Kotri barrage has been found to vary from eight MAF in 1999-2000 to 45 MAF in 1996-1997, which need to be conserved.
The situation of water storage reservoirs in the country is also discouraging because the storage capacity of the two main reservoirs (Mangla and Tarbela) is being lost at the rate of 0.033 MAF, and 0.15 MAF per year, respectively, due to silt deposition. Mangla reservoir has lost its storage capacity by 20 per cent and Tarbela by 43 per cent in year 2000.
According to an estimate, water deficit will increase from 41 MAF in year 2000 with population estimate of 148 million to 108 MAF in year 2013 with the projected population of 207 million. This is an alarming situation for all of us and every body needs to conserve every drop of water and make full use of it before it flows to the Arabian sea. The land wand water resources need to be developed to afford the survival of the growing population if proper measures were not adopted timely the nation would definitely be moving towards starvation. In view of this context, let us see how we can exploit our surface and ground water resources on sustainable basis.
Surface Water: About 106 MAF of water is diverted from rivers to the canals through head works and about 41 MAF is used by the crops giving an overall irrigation efficiency of about 40 per cent. About 61 per cent of water diverted from canals is lost during its conveyance and in the irrigation fields. No doubt this loss of water joins the invisible water resource--groundwater which is the cause of survival during this current drought period but also causes water-logging and salinity problems, However, significant room for improvement exists in the irrigation conveyance and application components, which can help us save precious water through lining canals and introducing high efficiency irrigation methods in the fields. Surveys need to be conducted to identify the sections of canals in sandy areas, which are causing high loss of water. These sections of canals can be lined in case enough funds are not available for lining the whole canals. Similarly watercourse improvement can also save significant amount of water. High efficiency irrigation methods such as sprinkler, drip, raised bed planting, zero tillage, and precision land evelling need to be demonstrated to the farmers based on their suitability under local conditions.
In year 1999-2000, Punjab received canal water supplies of 54.88 MAF (37.97 Kharif + 16.91 Rabi) (PSY, 2001). The annual canal water availability at the farm gate was 42.26 MAF with conveyance losses of 12.62 MAF. The crop use was 30.4 MAF after subtracting the application losses of 11.83 MAF. The area need to be irrigated was 11.01 Mha. The depth of canal water available from above mentioned supply was found to be 340 mm against the average annual crop water requirements of 12.50 mm. This analysis shows deficit of 910 mm, which may be fulfilled partially by rainfall (10 to 20 per cent) and partially by groundwater (40 to 60 per cent).
Groundwater: Groundwater is a natural resources and is also a kind of reuse of the surface water lost during its conveyance and application. The use of groundwater, however, needs very careful, however, needs very careful analysis of its quality before its application. The over exploitation of this resource not only causes mining of the aquifer but also deteriorates the ground water quality, which will turn our productive lands into barren lands after its use over a couple of years. The irrigated area and number of tube wells over the years have increased, which shows the application of groundwater for irrigation purposes (Table-I). The number of tube wells over the last decade (1991 to 2000) have increased at the rate of 60 per cent, 10 per cent, 63 per cent and 46 per cent in Punjab, Sindh, NWFP and Balochistan, respectively.
The Indus plain contains about 31 Mha cultivable land, which is underlain by sand alluvium to a considerable depth. Average annual recharge to the groundwater reservoir has been estimated to about 47 MAF (44 MAF from irrigation system + three MAF from rainfall) and groundwater pumpage of 40 MAE However, not all groundwater may be suitable for irrigation. Water quality can be a serious problem especially when the aquifers are being mined in case pumpage exceed the recharge rates particularly during the drought period. According to an estimate ground water table has gone down about five to seven m depth over the entire Punjab. If this situation continues, all the domestic and irrigation pumps will not be able to life water at the their present pump location. The groundwater quality is generally interior to surface water quality (average TDS of rivers, 200 ppm), however, depending on the location and depth of the wells. The groundwater carries more salts and if used for irrigation, those salts will be added to t he soils. These soils will turn into saline soils especially during the drought period when adequate water for leaching is not available. A scenario of salt addition to the soils has been studied based on different water quality of tubewells when used for irrigation of wheat crop (Table-II).
Precisely, tubewell water application of 37 cm depth with groundwater of quality 1000 ppm, 19 cm irrigation depth with 2000 ppm, and 12 cm irrigation depth with 3000 ppm will turn the top 30 cm soil depth of a typical non-saline sail into saline conditions. This shows the effect of tubewell water applications on the soils. Moreover, the farmer have to pay heavy cost to buy tubewell irrigation water. Generally, the cost per hour of a tubewell of one cfs capacity water varies from Rs.80/h to Rs. 150/h for electric and tractor driven pumps, respectively. Currently, the canal irrigated areas of Punjab received three to four irrigations from tubewells and thus the salt loading varied from 3000 to 12000 kg/ba along with payment of Rs.3000 to 4000 against Abian (canal water charges) of Rs.250 per ha for wheat crop. The cost of tubewell water varies from 12 to 16 times more than that of canal water supplies. Therefore exploitation of groundwater resources is not a sustainable practice both environmentally as well as economically. Similarly, excessive pumping also causes mining of the aquifer and results in further deterioration of ground water quality by upcoming of saline water into subsurface fresh water layer. The exploitation of groundwater resources needs very careful analysis to decide pumping rate, pumping schedule, as well as design of the well (dia and depth) to avoid saline water intrusion as well as salt addition to the irrigated agricultural lands of Pakistan.
REMEDIAL MEASURES MINIMISE SURFACE WATER
Conveyance Losses: The average annual irrigation water conveyance losses are about 48 MAF with 52 per cent losses occurring in the first phase of improvement, all the watercourses need to be lined and improved. In the second phase, surveys need to be conducted to identify the sections of the canals in sandy areas or sections causing high seepage losses. These sections of canals need to be lined in case enough funds are not available to line the whole canal length. The reduction in conveyance loss will not only prevent our soils becoming water logged but also save the precious water to sustain the agricultural production.
Minimise Water Application Losses in the Fields: This phase of improvement is difficult because new irrigation methods acceptable to the farming community need to de developed and demonstrated to the farmers. High efficiency irrigation methods used in the developed countries need modification to suit our local conditions and the local industry. For example, raingun sprinkler irrigation would be a better choice than regular sprinkler irrigation methods. Perforated irrigation pipes with adequate opening sizes can also be used as mini sprinklers with low pressure requirements. Similarly, conjunctive use of raingun sprinkler with surface irrigation methods particularly during early stages of crop growth or before planting (Rowni) can also help save irrigation water and sow the crops timely. Therefore, research needs to be conducted to modify and demonstrate new irrigation methods such as cognitive use of raingun sprinkler, perforated pipe irrigation, raised bed planting, precision land levelling, zero tillage tec hniques, and crop irrigation after completion of their successful research trials on farmers fields.
Groundwater: It is an excellent natural subsurface water reservoir, which needs to be taken care of the same way as surface water reservoir in terms of its pumpage, waterable lowering rates, quality and contamination, thickness of subsurface fresh water over the saline water. When we are proposing to reduce the water conveyance losses of our irrigation system, indirectly we are reducing the groundwater recharge. Therefore, we need to plan the recharge rates and select potential sites for recharge purposes during surplus water period especially during monsoon rainfall season. Monitoring of watertable depth needs to be carried out on Doab basis. Maps need to be developed to show groundwater recharge/discharge areas, thickness of subsurface fresh water layer, groundwater flow directions and groundwater quality maps using Geographical Information System (GIS). These maps and boundaries will lead to the development of Water District.
Water Districts: Water districts need to be developed based on water resources of the area. All water sources such a rainfall, surface water and groundwater need to be considered against crop water requirements of the district. Groundwater quality will be a key factor in deciding the boundaries of the districts. Water budgets of these districts needs to be carried out to assess water supply and demands of the districts. Alternative sources of water for the districts need to be studied in case there is shortage. Similarly, Ablana charges and other supporting facilities such as electric connection for tubewells, tubewell design, well dia and depth need to de designed. These water districts will also help manage drought situations, flood damages, erosion problems, and other water related issues. Water regulations for these districts can be developed keeping. In view the sustainable use of these water resources. Similarly, if groundwater is a critical resource for the district then key factors such as pumping rat es, pumping schedule, well capacity and installations need to be planned and executed. Water management packages for these districts can be developed, which would ultimately lead to the socially, economically, and environmentally feasible water management system of the district. Water management models for these districts can be developed following their hydrologic boundaries to predict the effects of different water management scenario on the use of water resources. Groundwater model can help plan recharge rates and pumping pattern for the water districts.
The cost of tubewell irrigation supplies for wheat has been found to be 12 to 16 times more than Abiana (canal water charges) along with salt loading of 3,000 to 15,000 kg. per hectare depending on tubewell water quality. Precisely, tubewell water application of 37 cm depth with groundwater of quality 1000 ppm. 19 cm irrigation depth with 2000 ppm, and 12 cm irrigation depth with 3000 ppm will turn the top 30 cm soil depth of a typical non-saline soil into saline conditions. Therefore facilities need to be provided for tubewell irrigation such as free supply of electricity and flat rate charges so that farmers may have surplus water for teaching the salts out of the root zone in order to maintain the soil productivity level.
Bringing new area under cultivation wit addition of new water reservoirs to the irrigation system is indispensable to replenish the depleted storage capacity of the existing reservoirs and also to meet the food and fibre requirements of our growing population, which will be doubled in the year 2025.
Desalination plants need to be developed in the coastal areas to provide fresh water using solar and wind energy.
New Sources of water such as treated sewage water can be used for recharging the aquifer as well as for irrigation purposes.
TABLE-I Area Irrigated by Canals and Tubewells 1996-97 1997-98 1998-99 1999-00 PUNJAB - Canals 4.17 4.08 3.88 3.93 - Tubewells 9.04 9.589.67 9.92 SINDH - Canals 2.41 2.43 2.53 2.39 - Tubewells 0.13 0.13 0.13 0.13 N.W.F.P. - Canals 0.35 0.38 0.39 0.39 - Tubewells 0.54 0.56 0.55 0.53 BALOCHISTAN - Canals 0.42 0.42 0.40 0.40 - Tubewells 0.41 0.42 0.40 0.40 Source: Pakistan Statistical Yearbook (2001) TABLE-II Amount of Salts Added to the Lands from Tubewell Irrigated Action to Wheat Crop No. of Irrigation 1 2 3 4 5 Depth of Water Applied (cm) 10 20 30 40 50 Groundwater Quality (ppm) 1000 1000 1000 1000 1000 2000 2000 2000 2000 2000 3000 3000 3000 3000 3000 Salts Added (kg/ha) 1000 2000 3000 4000 5000 2000 4000 6000 8000 10000 3000 6000 900% 12000 15000 Water Charges * (Rs./ha) 972 1945 2917 3890 4862 * Rs.100/h for 1 cusec (cfs) tubewell capacity TDS < 1000 ppm (Fresh Water) TDS, 1000 to 2000 ppm (Usable after mixing with fresh water) TDS > 3000 ppm (brackish, not suitable for irrigation)
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|Date:||Jul 1, 2002|
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