ACHIEVEMENTS AND ISSUES OF IRRIGATION IN THE 20TH CENTURY

Transcription

1 ACHIEVEMENTS AND ISSUES OF IRRIGATION IN THE 20TH CENTURY Pub. No.WRRI(99):1 Dr. Shahid Ahmad WATER RESOURCES RESEARCH INSTITUTE NATIONAL AGRICULTURAL RESEARCH CENTRE ISLAMABAD

2 ACHIEVEMENTS AND ISSUES OF IRRIGATION IN THE 20TH CENTURY ** Dr. Shahid Ahmad * Abstract Irrigation plays a dominant role in irrigated agriculture as it provides 90% of the total wheat production of the country and almost 100% of cotton, sugarcane, rice, fruits and vegetables mainly within the Indus basin command area. Also, the irrigation sector plays a vital role in the industrialization process of Pakistan with the production of cash crops and dairy cattle. The irrigated area has increased from 9.1 million hectares in 1947 to about 18 million hectares in The doubling in irrigated area in 50 years is a major factor in increasing agricultural productivity and production. Coupled with increases in cropping intensity of 60% in 1947 to 120% in 1998 provided a 4 fold increase in production compared to The increase in productivity due to Green Revolution was primarily due to the improved seed, use of chemical fertilizers and increased water supply. With a population of 132 million today, that is expected to reach to 171 million by the year 2010, the demand for food products is expected to continue to grow. The problems associated with irrigation system are the main cause for low productivity and the sector has become increasingly the target of criticism and considered as the main cause for productivity problems in agriculture because of water scarcity, in-efficiency, inequity and sustainability issues. The paper highlighted the achievements made during the last 50 years while addressing these issues. The major unresolved issues were identified which still require technological development, managerial and institutional reforms and mechanisms to attain sustainability of irrigated agriculture. There is a need to initiate comprehensive planning and integrated development and management of irrigated agriculture in the country. 1. Introduction The importance of the agriculture sector in the economy of Pakistan can be viewed from the factor that it contributes 25% to the gross domestic product of the country and provides job opportunities for 55% of the labour force. It also accounts for 80% of the total export earnings of the country (GOP 1998a). Within the agriculture sector, irrigation plays a predominant role as it provides 90% of the total wheat production of the country and almost 100% of cotton, sugarcane, rice, fruits and vegetables mainly within 16.4 million hectares of the Indus basin. Also, the irrigation sector plays a major role in the industrialization process of Pakistan with the production of cash crops (cotton, sugarcane, citrus, mango) and dairy cattles. During the 60s and 70s, the country benefitted from the technological development of the Green Revolution through improvements in self-reliance of agriculture and food products due to significant increases in cropping intensities and crop yields. The irrigated area has increased from 9.1 million hectares in 1947 to about 2

3 * Director, Water Resources Research Institute, National Agricultural Research Centre, Islamabad. ** Paper prepared for presentation in the National Seminar on "Achievements and Issues of Water in the 20th Century" July 1999, organized by PCRWR, Islamabad. 18 million hectares in 1998 (GOP 1998b). This doubling in irrigated area in 50 years is a major factor in increasing agricultural productivity. Coupled with increase in cropping intensity of 60% in 1947 to 120% in 1998 provided a 4 fold increase in production compared to 1947 level of productivity. This four-fold increase was mainly due to increase in water availability from both surface and groundwater sources. This is a sufficient indicator that water contributed more than Green Revolution for enhancing production and productivity. By the end of 80s, several signals suggested that the period of agricultural output growth was over, with the productivity per unit of land of the main crops becoming stagnant or even following a decreasing trend (GOP 1998b; World Bank 1994; Bandaragoda and Firdousi 1992). With a population estimated at more than 132 million inhabitants today, that is expected to reach 171 million by the year 2010, the demand for food products is expected to continue to grow. Thus, unless there are significant improvements in agricultural productivity and total production atleast in the same order of magnitude as those recorded during the Green Revolution period, the imbalance between supply and demand of basic agricultural goods is expected to increase in the future and to threaten the self-reliance objective of Pakistan. The problems associated with irrigation system are the main cause for low productivity of the Indus basin. Although the benefits of irrigation per unit area are fully recognized under the arid environment of Pakistan, little would grow without irrigation, the irrigation sector has become increasingly the target of criticisms and considered as the main cause for productivity problems in agriculture because of water scarcity, in-efficiency, inequity and sustainability issues. The challenges confronted by the irrigation sub-sector are: canal water resources are inadequate to meet the requirement; water distribution is not equitable due to increased competition for scarce resource; water allocation to different canal commands is based on design rules but requires adjustments because of recent groundwater exploitation in terms of quantity and quality; measurement of flows, communication and processing requires to build irrigation operational management information considering the country and site-specific requirement. The paper includes a review of past achievements during the 20th century in the sub-sector of irrigation and outlines the major issues which have to be targeted in the 21st century. Therefore, this paper is an effort to provide basis for building vision for

4 2. Achievements A review of achievements in the irrigation sub-sector during the 20th century was conducted considering four major thrust areas: a) efficiency; b) requirement; c) equity; and d) sustainability. The effort made in this paper is just a beginning and has to be further strengthened by adding additional information. Because such an effort requires much more time to reach to a point leading towards identification of real-issues which have to be addressed in the next century Efficiency Irrigation efficiency in this paper is referred to the ratio of the volume of water required for a specific beneficial use as compared to the volume of water delivered for this purpose commonly interpreted as the volume of water stored in the soil for evapotranspiration compared to the volume of water delivered for this purpose, but may be defined and used in different ways (Jensen et al. 1990). The recent concept of Global efficiency put forward by IIMI is not adopted in this paper because of serious concerns of its application under site-specific limitations (rights, quantity, quality). This school of thought yet has to prove practical application of this definition Canal Conveyance Losses The Indus basin irrigation system constitutes main canals, branch canals, distributary canals, minor canals and watercourses. There has been a number of studies conducted in the past to estimate conveyance losses of earthen canals. The review of over a dozen studies conducted by various institutions revealed that conveyance losses in main canals and branches varied between 15-30% using the inflow-outflow method (Ahmad 1993a). The earlier studies conducted by Kenedy, Benton, Higham, Blench and Khangar indicated losses on the lower range of 15-20%, whereas studies conducted by various consultants indicated losses in the range of 20-30% (Harza 1963; IACA 1966; LIP 1966). WAPDA (1979) presented results of water losses in canals considering canal dimensions and nature of soil formation over which canal is located. The length of canal system, its discharge and wetted perimeter were major parameters utilized in this study. The soils of the Indus basin were classified into four categories and weight was assigned to each category accordingly. Canal loss functions were developed for four categories of the canal system. The WSIP (1990) provided a synthesis of the work done by WAPDA on annual canal conveyance losses for 24 canal commands in the Punjab province, 5 canal commands in the NWFP and 14 canal commands in the Sindh province. Data for both the non-perennial and perennial canal commands were recorded. The annual canal losses in the Punjab's 24 canal commands varied between 13-36%, whereas in the NWFP these varied between 12-24% for the 5 canal commands. The annual canal losses in the Sindh's 14 canal commands varied between 15-25%. The average annual canal losses computed were 23, 12 and 20% for the canal commands of the Punjab, NWFP and Sindh provinces, respectively. On basin-wide, these losses are around 21%. 4

5 The canal losses were further fine tuned by WAPDA using the wetted perimeter of canal and these were around 23% on basin-wide basis. The recently lined Chashma Right Bank Canal, Stage-I, in the NWFP has severe seepage problem particularly in the unlined reach. A number of remedial measures were taken, and the problem is under control. The analysis of seepage data collected during shows that 95% confidence interval of average seepage loss rate in the project area for earthen reaches of the canal is ± cusecs/msf and that for the lined reaches is ± cusecs/msf of wetted area. For the sake of comparison, the loss rate adopted in the design was 8 cusecs/msf and 2 cusecs/msf for unlined and lined sections, respectively. The expected seepage loss revised downward from 385 to 327 cusecs. The difference between the average seepage from brick lined and plane-cement-concrete lined parts of the canal is practically insignificant. The measurements also show that there is a little correlation between seepage loss rate and inflowing discharge in the canal (Siddique, et al. 1993). The IWASRI (1993) organized an international seminar on "Canal Lining and Seepage" and the proceedings provide a comprehensive documentation of experiences in Pakistan and elsewhere. Later on a comprehensive review of seepage losses from unlined and lined canals in Pakistan and elsewhere was done by IWASRI and report provides criteria for adoption of seepage estimation methods and lists the inherent applicability limits for suggested methods (Shahid et al. 1996). Most of these loss measurements especially in the early periods are based on flows diverted to canals and deliveries to branch canals and distributaries where measurements were made using discharge regulating structures and downstream gauges. The recent studies conducted indicated that the downstream gauge rating needs periodic adjustments. The most preferred approach is to simultaneously calibrate the downstream gauge and the discharge regulating structure, which will save time in the long-term by facilitating frequent adjustments to the downstream rating (Vehmeyer et al. 1998). Therefore, the canal losses might be different than estimated by WAPDA and PIDs as actual flows are much different than the designed flows. Therefore, further improvements are required in discharge measurements Watercourse Conveyance Losses The conveyance loss measurement studies for the tertiary system namely watercourse were initiated during earlier periods of system development by Kenedy, Benton and Blench which were 27-29% (Hunting Technical Services 1965). The systematic work on watercourse loss measurement was initiated jointly by the Colorado State University and the WAPDA using inflow-outflow method with cut-throat flumes (Ashraf et al. 1977). On the basis of two systematic studies of 40 and 61 watercourses, the actual watercourse losses were 47 and 45%, respectively, which were higher than earlier studies and especially from the 10% loss reported by the Punjab Irrigation Department based on seepage losses in watercourse sections constructed at the research institute instead of farmers watercourses. The actual conveyance loss includes all the operational losses 5

6 alongwith the seepage loss (PARC-FAO 1982; WAPDA 1979; Ashraf et al. 1977). In these studies, the watercourses were selected under perennial and non-perennial canal commands covering all the four provinces. Trout and Kemper (1980) presented constant loss rate function which can be used to estimate conveyance losses for a given length of the watercourse. They recommended loss rate of 2.8 and 1.46 % per 100 m length of channel for unimproved and earthen improvements, respectively. The loss rate function developed for perennial and nonperennial canal commands can be used on wider range considering various site-specific situations. The loss rate function developed by Trout and Kemper (1980) has to be used considering the watercourse condition and the Warabandi schedule because water is flowing in the channel based on a fixed-rotation system. Therefore, length of the channel has to be seen in the context of Warabandi at each square Nacca. Ahmad and Khan (1990) developed an approach where they have used the loss rate function based on the Warabandi schedule of Mogha # 62394L at Bhalwal, Sargodha. The average watercourse losses were around 32% over the watercourse length during a particular rotation schedule. The average watercourse losses were 16, 35 and 46% at the head, middle and tail-end reaches, respectively. The study revealed that watercourse losses as presented by WAPDA (1979) and Ashraf et al. (1977) represent the total watercourse length especially the tail-end reaches, which are higher than the average water losses in relation to the Warabandi schedule. Ahmad and Khan (1990) also presented comparison of water losses in main watercourse and branch watercourses under the MONA SCARP Unit. They were of the opinion that in long watercourses of 9 km length, the main watercourse contributed 93% to the total conveyance losses because it is in operation for 100% time of each turn. The field watercourses were in operation of about 4.3 hours per week per square of the selected command and length was also limited. The recent results reported by MREP in 1993 based on monitoring irrigation water delivery in a sub-system of Chabba distributary offtaking from the northern branch of the Lower Jehlum canal. The study covered the water loss measurements on distributary and all the watercourses. The average loss in watercourses was around 43%, whereas it was 20% in the distributary. The authors were of the opinion that Chabba distributary is one of the most efficient distributary of the branch canal. The average loss in the distributary sub-system was around 54% (Cheena and Piracha 1993). The reliability of the analysis is questionable as contradictory conclusions were drawn. Therefore, more systematic results were selected for this paper. However, the most recent study confirmed the previous results of the conveyance losses in watercourses. The acceptable figure of watercourse conveyance losses in Pakistan is around 40% for un-improved earthen watercourses. The earthen improvements can reduce the losses to around 15-20% depending on level of improvement and soil conditions (PARC-FAO 1982). 6

7 Field Application Losses The field application losses measured under 40 watercourses and 61 watercourses studies were 50 and 30% under both the perennial and non-perennial systems, respectively. However, these were 28-29% under perennial canal command systems. The acceptable figure on basin-wide is 25% as most of farmers are practicing deficit irrigation (PARC- FAO 1982; WAPDA 1979). The recent studies conducted in the Chabba distributary of Lower Jehlum canal indicated field application losses of 30%. This is a confirmation of the previous results (Cheena and Piracha 1993) Irrigation Methods and Measures to Improve Application Efficiency In Pakistan basin irrigation is practiced in fields which are not precisely levelled and thus application and uniformity efficiency is low (Ali et al. 1993). The precision land levelling started under the On-Farm Water Management Programme helped to improve application of water but this practice could not be linked with selection of appropriate irrigation method. Border irrigation is more efficient than basin and requires little or no precise levelling. Streamsize, width of border, length of border and infiltration are the parameters while designing the irrigation method. The larger streamsize of 2-3 lps per meter performed better than 1 lps per meter. The application efficiency of level borders is higher than level basins (Ali et al. 1993; Piracha et al. 1989). The planting of cotton on broadbeds with row to row spacing of 75 cm resulted in 30-35% increase in yield compared to flat planting. This increase in yield was also accompanied with savings in water of 28%, 40-45% and 40-45% under furrow, alternate furrow and furrow-bed irrigation compared to basin irrigation (PARC-FAO 1982). These results were further verified by PARC, IIMI, LIM and UAF under a number of studies conducted during the 90s (Berkhout 1997; Javaid and Khoso 1991; Rafiq and Qureshi 1991; Javaid et al. 1988). The Kahlown et al. (1998) presented results of improved methods of irrigation for cotton under varying water-table depths. Savings in water applied using furrow-bed method compared to basin irrigation was 61, 60 and 59 percent at water-table depth of 0-1, 1-2 and 2-3 m, respectively. For wheat crop, the maximum water saving of 68 percent was achieved with 120 cm bed at a water-table depth of 0-1 m. The furrow-bed system is most suitable for all conditions of water-table depths. It also helps to reduce leaching of nitrates and thus increase the fertilizer use efficiency. The cost of planting in bed is higher than flat planting in basin. Thus, there is a need to initiate studies on permanent furrow-bed system compared to temporary system in conjunction with nature farming to enhance macro/micro-organisms in soils. Sprinkler irrigation is feasible in Pakistan and potential introduction requires indigenization of the system and local manufacturing to reduce the cost. The WRRI-NARC selected two raingun sprinkler models which are now being manufactured in collaboration with the local industry. The high pressure pumps are locally produced and can be coupled 7

8 with locally produced electric and diesel prime-movers. The local pump industry is now producing the complete system at a cost of around Rs. 10,000 per acre for systems not less than 5 acres (Ahmad et al. 1993). The UV stabilized pipes of black carbon polyethylene are produced locally for conveyance of pressurized water. These pipes are normally less than 50% of the cost of galvanized iron and can be used on surface or under burried conditions. The WRRI-NARC further worked with the plastic industry to indigenize the trickle irrigation systems in Pakistan. The system components including emitters, connections, filters, laterals, manifolds, mainline and fertilizer injectors are all locally produced and the cost is around Rs. 12,000 per acre excluding the pumping system (Moshabbir et al. 1993). The costs per acre are given based on 1999 price levels. Field experiments on supplemental irrigation in Barani lands on wheat crop indicated that crop can be planted on time by applying a minor irrigation of only 10 mm as Rauni. The application of Rauni and plantation of wheat in early November doubled the yield of wheat compared to Barani plantation. The Rauni irrigation increases the crop stand in addition to early planting. Further irrigations to wheat during dry spells can increase the yield to 3 fold. The Barani yields are around 1.0 tonne/ha in an average year (Ahmad et al. 1999). In the context of a fixed and short water supply system of the Indus basin, the challenge of the enhanced productivity can only be met by improving productivity of irrigation water supplied. It means we have to use our limited water resource optimally. During the initial crop growth period, water uptake by the plants is lower as compared to that at the later stages. Such low requirements are quite difficult to be applied by flooding the usual way adopted in Pakistan. However, this purpose can be attained by use of a pressurized irrigation system. Moreover, adoption of pressurized irrigation practices can help to manage root-zone salinity especially in sodic soils (Ahmad et al. 1996) Measures to Reduce Canal Conveyance Losses Comprehensive reviews of canal lining in the Indus basin were presented during late 50s. The initial efforts were started as early as 1910 when Curry initiated lining experiments in the Jhang canal. The seepage was 1.47 to 4.83 cusecs per million square feet and now this canal is part of India after independence in These lining efforts were expanded to cover Trimmu-Sidhnai link and Haveli canal (Ahmad et al. 1957; Ahmad and Razaq 1960). The lining experiments were extended to many other canals. Haveli was the first lined canal constructed in Since then different types of canal lining techniques were tried. Initial design consisted of two layers of tiles with an impregnation of 1/2 inch cementsand plaster. Haveli was the first canal of this type, it was followed by Balloki-Sulemanki, Sidhani-Mailsi-Bahwal and Chashma Right Bank Canal (CRBC) stage-i and partly stage- II. Sidhnai-Mailsi-Bahwal is the only canal in which coating of 1/8 inch thick bitumen was also used (Ahmad 1993a). Double tiles design was slightly changed while constructing Thal Mainline Lower 8

9 and Bambanawala-Ravi-Bedian link. In these canals, the bottom layer of tiles was replaced by plaster of thickness varying from inches (Ahmad 1993a). A filter of 3 inch-thick of 1:30 cement:sand ratio was used under the lining of Balloki-Sulemanki, CRBC stage-i and partly in stage-ii. The purpose of lining was to control high water-table but the damages were primarily due to the problem of waterlogging. Seepage from lined canals has never been measured. These measurements are very much necessary for the Balloki- Sulemanki and Haveli canals. Both have lined and unlined sections. The top 3 or 4 feet of lining always appears damaged due to weed growth and salts due to capillary rise. Frequent cutting of weeds is possible. Salts accumulation reduced the life of tiles to years. Repair of damaged sections is difficult and requires form of pressure release filter (Ahmad 1993a). Brick mortar lining has been used in the country and till recently it has been the choice type. In the recent decades concrete lining started on account of deterioration of brick quality. Out of a total of 930 miles of lined channels in punjab, the concrete covers 400 miles. A typical framework has been developed for concrete lining to improve lining quality, allowing medium workability, good compaction and finishing. Framework produces better pannels, density, surface levels line and grades. Material availability and quality control is easier in concrete. Life depends on quality and construction. Lined reaches improved distribution and reduced waterlogging. Maintenance cost is lower in lined channels than earthen channels (Zaidi 1993). In NWFP, now much more emphasis is placed on soil compaction of the subgrade and using appropriate materials in the lining joints to reduce seepage. In addition design criteria has been improved such as flatter side slopes and more realistic values of mannings roughness coefficient (Khan 1993). In the Command Water Management project two small scale distributary canal systems of the Rohri canal were lined having a discharge of upto 30 cusecs. The cost of lining was Rs. 1.6 million/mile. The lining of 140 miles was done to evaluate the technique. The benefits include saving in seepage, equitable and assured supply, extra area under irrigation, increase in crop yield, timely availability, increased income, increased revenues and reduction in O&M cost (Junejo 1993). Similar results were obtained under the ISRP lining programme in Sindh where concrete lining helped to improve the canal hydraulic performance which contributed towards assured supplies to farmers that was not available to them in the past. Lining under these projects have been insufficiently monitored and evaluated and apparently more work is needed that should be done on unified basis (Ehsan et al. 1993). During initial years of CRBC operation, seepage losses had relatively high values in the unlined and relatively low in lined sections, however, at present comparable values have been demonstrated for both the sections. Actual roughness of the brick and concrete lined sections is higher than the designed value of This increase in roughness has obvious implications as reduced canal capacity will constrain every day operation in future (Habib and Restrepo 1993). Observations on the hydraulic changes of secondary canals in Punjab indicated that 9

10 performance improvement objectives are not always achieved. If lining is justified on the basis of water savings through reduced seepage losses, then tail-end reaches should receive improved water deliveries. Observation in two distributary canals following lining do not demonstrate significant improvement in tail-end conditions. justification of lining on the basis of more stable conditions is also hard to identify; reduction in the variability of discharge was not observed. Financial analysis of a recent canal lining experience in Punjab indicates that water savings would have to be unrealistically high, and sustained for long periods, if initial capital cost is to be repaid through improved water conveyance efficiency. Furthermore, the hydraulic improvements achieved through alternative interventions appear to strengthen the argument that lining can be justified only under special conditions, rather than adopted as a wholesale approach to solving water distribution problems. Whatever the intervention, management control must be strengthened; lining is not a substitute for effective canal operational and maintenance inputs (Murrary-Rust 1987; Garin et al. 1998). Further economic analysis indicated that canal lining is not feasible on economic efficiency criteria in the freshwater zone but feasible in saline water zone based on command water management studies. The cost of one acre foot of water saved through canal lining is Rs. 988/acre foot, whereas the cost of pumping water is Rs. 210/acre foot of water by tubewells. Therefore, lining must be related to the site-specificity and objective (Shafiq and Naqvi 1993). Recent development of reinforced geosynthetic film provided a right material for lining of canals but its economics is still a question unless it is manufactured in Pakistan (PARC 1994) Measures to Reduce Watercourse Conveyance Losses The pioneering work of watercourse lining was initiated during early 70s at the MONA Reclamation Experimental Project, Bhalwal on two watercourses with brick masonry and cement concrete, in rectangular and trapezoidal designs with thickness of walls ranging from 4.5 to 13.5 inches. The cost-effectivity was studied for various techniques. In addition, soil-cement block lining, broad-bed lining, pre-cast RCC slab lining, partial lining, V-shaped lining were tried with different economics and sustainability (PARC-FAO 1982). The 9 inch brick lining technique was adopted by the provincial On-Farm Water Management Programmes in the country during late 70s and early 80s in the pilot project financed by the USAID and continued under the OFWM-I and II projects financed by the international banks and other donors like OECF. In the OFWM-III, pre-cast lining techniques developed during early 80s and perfected during late 80s were used on limited scale. The OFWM never tried to continue search for cost-effective lining techniques and by and large the programme has been following traditional brick lining techniques of 9 inch thickness. Because of the high cost, the lining length is limited to a maximum of 30% length of the watercourse and for larger length watercourses this percentage is further reduced to even 10%, i.e. the ADB financed project for the Patfeeder Canal command. 10

11 The 9 inch brick lining although was costly but helped to reduce the seepage losses significantly. The losses of earthen watercourses were reduced to 20-25% after lining which corresponds to 8-10% over the watercourse length (Cheena and Piracha 1993). The recent monitoring studies conducted by MONA Reclamation Experimental Project indicated that cost-effective lining techniques used years ago are still performing reasonably which is a good indicator of long life of watercourse lining because of quality of construction due to beneficiary participation (Personal Communication) Crop Water Requirement Consumptive use of water, or evapotranspiration (E t ) is one of the most basic components of the hydrologic cycle. Consumptive use, which includes evaporation of water from land and water surfaces and transpiration by vegetation, continues to be of foremost importance in water resources planning and management and in irrigation development. As the water retained in plant tissues is minor relative to the amount used in E t, both the terms are used for same meaning (Jensen et al. 1990). Consumptive use of water information is necessary in planning and operation of water resource projects. Consumptive use is involved in problems of water supply, both surface and groundwater; water management; and in the economics of multiple-purpose water projects for irrigation, power, water transportation, flood control, municipal and industrial water uses; and wastewater reuse systems. In Pakistan, this information is now crucial for resolving issues related to water apportionment, allocations, development of new storages and disputes related to regional and environmental issues. Considerable work has been done on consumptive use of water for crops by various workers in Pakistan. Most of the work done during early periods (47-72) on estimation of consumptive use of water of crops is either based on estimations made in lysimeters or from calculations using empirical coefficients developed from climatological data. The work on estimation of consumptive use of water by crops in the field based on soil moisture depletion was initiated during mid 70s, when PARC initiated a national programme on "Consumptive use of water for major crops under optimum management conditions". The findings are reported as follows: By Computations Blaney and Criddle (1957) calculated the evapotranspiration amounts for wheat to be 400 mm. Similarly, Asghar and Ahmad (1962) and Revelle (1964) reported that evapotranspiration amounts in case of wheat was mm. The Hunting Technical Services (1966) calculated consumptive use of water for wheat in Hyderabad area to be 414 mm. These findings were based on calculations using climatological data. Dastane (1966) worked out correlations between values of actual consumptive use and those computed by using various empirical equations in optimum moisture regimes. In case of wheat, the correlation values for Penman, Thornthwaite and U.S. Open Pan Evaporation methods were 0.982, and 0.998, respectively. He reported that seasonal 11

12 evapotranspiration in case of wheat was 330 mm. The Harza Engineering Company International (1968) determined the consumptive use of water of various crops using the evaporation index method. The findings were based on studies carried out in USA. The computation from USA to determine crop coefficients were modified to made them applicable to conditions in Pakistan. Based on calculations, they reported that estimated consumptive use of water for wheat was 403 mm. Clyma (1973) advocated the Jensen-Haise method for estimating evapotranspiration for crops. He estimated mean annual reference evapotranspiration for Sargodha to be near 1830 mm per year. With wheat during Rabi and cotton during Kharif, evapotranspiration ranged from 1100 mm in a wet year to 1200 mm in a dry year, he calculated net irrigation requirements for wheat grown in Sargodha under wet and dry seasons as 173 and 410 mm, respectively. Ahmad (1982) presented calibration coefficients for Jensen-Haise equation for a number of locations in Pakistan representing varying agroclimatic zones. Ahmad (1985a) presented prediction models for reference crop evapotranspiration in Punjab of Pakistan for eight selected crops. He further reported basal crop coefficients for eight selected crops which can be used in computer models for scheduling irrigation (Ahmad 1985b). Hargreaves and Samani (1985) presented monthly reference crop evapotranspiration for a number of locations in Pakistan. This is the most practical method as the data required is only mean temperature and thus can be used for countrywide computations because such data are easily available in Pakistan. The selection of method for estimating reference crop evapotranspiration depends on: a) objective of computations and availability of quality data for real-time scheduling or planning purpose; b) capacity of the users' in the use of such equations; c) acceptance of the method in the country or among the scientists. The Hargreaves (1985), Jensen-Haise (1963) and Blanney-Criddle methods can be used for planning purposes where average monthly values are required. For real-time scheduling on daily basis Penman (1963) and Penman Montieth method (Allen et al. 1989) can be used for more precise estimates of reference evapotranspiration (Ahmad 1982; Ahmad and Heermann 1992). The ICID presented six irrigation scheduling models out of which one can be used for scheduling irrigation under less flexible irrigation systems at the field and at the farm level for selected crops (ICID 1992; Ahmad and Heermann 1992) Lysimeter Studies In a lysimeter study Asghar et al. (1962) found that wheat crop used 505 mm of water during its growing season, when the water-table was kept at 3.2 meter. In a similar lysimeter study Hussain (1970) calculated the water requirements of crops in West Pakistan. He found that the consumptive use of wheat was 337 mm. He further reported 12

13 that the consumptive use for wheat (indigenous) and wheat (Maxi-Pak) was 339 and 522 mm, respectively. Using climatological data, the author worked out the Blaney-Criddle crop coefficients (K) for wheat as 0.5. Ali et al. (1973) calculated the consumptive use of common crops in lysimeters keeping the water-table at various depths. They used climatological data and worked out empirical consumptive use coefficients. They found that the consumptive use of wheat (Maxi-Pak) grown at water-table depths of 1.5, 2.1 and 2.75 meter was 546, 483 and 488 mm, respectively. PCRWR published a number of reports of consumptive use of water for crops under varying groundwater table depths at Lahore and Tandojam. The results of these studies have limited application especially the Lahore lysimeters are now surrounded by urban buildings and do not represent agricultural environment. Furthermore, these lysimeters are non-weighing type and seepage control is very difficult under inflow-outflow system Field Studies Khan et al. (1968) while comparing the effect of varying quantities of water on yield of wheat (Maxi-Pak) found that the water requirements of wheat was 523 mm. They observed that this data of water was optimum for obtaining maximum yields. These findings were not based on actual consumptive use estimation. Hussain and Asghar (1969) reported that water requirements of wheat grown at various places in West Pakistan varies from 343 mm to 606 mm. Un-published data from the Ayub Agricultural Research Institute, Faisalabad and MONA Reclamation Experimental Project, Bhalwal indicated that wheat should be irrigated at 25% of the available moisture left in the soil or at 75% depletion of available water. Systematic work on consumptive use of water in relation to moisture stress was initiated by PARC during 1975 which continued for over 10 years in six major agroclimatic regions of Pakistan. The studies were based on field experimentation using four moisture levels (management allowed deficit) and two fertilizer levels with an objective to evaluate yield of crops as a function of soil moisture stress. Gravimetric moisture measurements were used for scheduling of irrigation and to study dynamics of soil moisture. Jensen-Haise equation and pan evaporation data were used to estimate reference crop evapotranspiration and crop coefficients were estimated on 10 daily basis. The information generated is very much beneficial for design and operation of irrigation schemes and managing irrigation at the farm level. PARC (1982) reported results of consumptive use of water, moisture stress-yield functions and crop coefficients for wheat, maize, cotton, sugarcane and soybeans for six agro-climatic regions of Pakistan for experiments conducted under field conditions, where water-table was below 6 meters. PARC (1993) further reported results of consumptive use of water, moisture stressyield functions and crop coefficients for 12 crops grown in various agro-climatic zones of Pakistan. The results of 17 crops grown under various agro-climatic zones are now 13

14 available for planning and design of irrigation schemes in the country. The moisture stress-yield functions indicated that most of the grain crops like wheat, maize, sorghum and millets can be irrigated at 75% depletion of available soil moisture without loosing any significant yield. Thus management allowed deficit for these crops should range between 50-75%. Cotton crop behaved differently where further stress did not affect the yield rather it helped to maintain the yield. In addition first irrigation should be scheduled days after planting. An other management strategy is to terminate irrigations atleast 30 days before harvest so that dry conditions favour opening of bolls to have uniform harvest. The use of rain water should be linked to achieve effective leaching of salts from the profile Equity The low irrigation efficiency of the Indus basin of only 34 percent means that 66% of water diverted to the canal system is not available for crop consumptive requirement (Ahmad 1990). Canal water supplies are highly inequitable, variable and unreliable (Bhutta and Vander Velde 1992; Kuper and Kijne 1993; Ahmad 1993b; Vander Velde 1990). The operational performance of the public tubewells is poor, which results into utilization rates and discharges lower than the designed level (Malik and Strosser 1994). Poor maintenance, lack of implementation of operational rules, inappropriate information system, local preference by operators that increase downstream variability, and interference by notables in the operation of the irrigation system, or lack of interest by the department staff in improved operational management are reasons explaining the poor performance of the irrigation system. These factors contribute in widening the inequity between head and tail reaches. Ahmad and Khan (1990) presented results of watercourse conveyance efficiency of 84, 65 and 54% at the head, middle and tail, respectively for long watercourses of SCARP areas. This is a good indicator of inequity in water availability at the farm level and thus demands to review the concept of Warabandi, which is based on time equity instead of volume equity. The situation becomes worst for the tail-end reaches of the canal, distributary and watercourse. Tareen et al. (1996) presented water distribution at the secondary level in the Chishtian sub-division and indicated that inequity exists at the secondary level. Maintenance and operation of irrigation systems has been constrained by inadequate allocation of funds in the budgets of the provincial irrigation departments. The low level of funding is partly related to the existing gap between water charges collected from water users and actual cost of operation and maintenance of the system. This is primarily due to the high operation and maintenance costs of public tubewells. The overall financial constraints faced by the provincial irrigation department further accelerate the issue of inequity (John Mellor Associates 1994). Inadequate financial allocation coupled with lack of appropriate methodologies for optimal allocation of these scarce resources and poor quality control associated with contract works (Vander Velde 1990), has led to deferred maintenance, with negative impact on canal performance and equity in water distribution. 14

15 2.4 Sustainability Although investments in drainage have been significant in Pakistan during the last two decades, waterlogging still affects large tracts of land, with more than 22% of the total gross command area of the Indus basin irrigation system having water-table within 1.5 meters (World Band 1994). Salinity and sodicity also constrain farmers and affect agricultural production. These problems are further exacerbated by the use of poor quality groundwater (Kijne and Kuper 1995). In fresh groundwater areas, excessive pumping by private tubewells leads to mining of the aquifer (NESPAK 1991). It is necessary to state that some of these problems are not new in the irrigation sector of Pakistan. Dry tails, poor maintenance, users' interference, waterlogging and salinity, have always been part of the history of irrigation in Pakistan. For example, as early as in 1895 measures were implemented to control waterlogging (Kuper 1997). However, the negative impact of these problems could then be compensated at the macro level by the construction of new irrigation systems that constituted the major public interventions in the irrigation sector for a very long period. In the 80s, there was a considerable recognition of the inadequacy of the purely supply-based engineering biased interventions for tackling the problems faced by the irrigation and agriculture sectors. New approaches were proposed that included institutional components. Examples of such approaches include: the On-Farm Water management projects that promote the development of Water Users' Associations at the watercourse level (Colorado State University 1976); the SCARP Transition projects that aim at reducing public involvement in the groundwater sector by closing down or transferring public tubewells to the water users (World bank 1988); or the Command Water Management Program that promoted water users' involvement in the maintenance of the irrigation system up to the distributary head (World Bank 1996). Also under the pressure of donors, there have been discussions on the need to increase water charges to decrease the gap between revenues from the irrigation sector and operation and maintenance costs. Although conditional loans for several projects, the political decision to increase water charges has been postponed. Only recently some of the provinces have decided to increase water charges. However, despite the apparent change in philosophy that guided interventions in the irrigation sector, only the engineering and agronomic components of these new approaches were successfully implemented. A typical example is the On-Farm Water Management Projects in the provinces, where watercourse improvement and agronomic interventions (the engineering and agronomic components) have been implemented in large number of watercourses while few Water Users' Associations (the institutional component) have been developed in a sustainable manner. Reasons explaining this lack of success may be related to inadequate approaches for local conditions; the absence of addressing real needs for Water Users' Associations within the watercourse command area; the lack of local support and appropriateness of changes brought by outsider; the meager qualified human resources (i.e. technical staff from agriculture department with little training in mobilization and water management extension) allocated to the implementation of these projects; and the incentives for implementation staff closely tied to construction progress rather than to institutional progress and development impact (World Bank 1996). The 15

16 opinion of the World Bank is partially correct because the problem is mainly with the project design instead of the implementation. The project targets are focussed on physical outputs, whereas very little resources were kept for social mobilization and institutional reforms uptil OFWM-III project. Even in the OFWM-IV project, the role of social and institutional component is assigned to consultants. In the past, the consultants teams of OFWM use to have background in institutional aspects but they could not create impact on the implementation of the project. What needed is the reorientation of the Field Teams and supervisory staff through integration of institutional, management and physical components. More recently, in recognition to the current problems in the irrigation sector and under pressure from international lending agencies, drastic changes in irrigation sector policies have been proposed (World Bank 1994). These changes, in line with the worldwide recognition of the economic value of water, included the privatization of the irrigation sector and development of water markets in order to achieve financial autonomy of the sector and economic efficiency. Several rounds of discussions were held between the major stakeholders of irrigation system in Pakistan, i.e. government departments at the provincial and federal levels, farmer organizations, politicians and donors to discuss the proposed and highly controversial changes. The different stakeholders eventually agreed on the need to decentralize, instead of privatize, irrigation system management and to promote a participatory management mode. In short, the final proposal opted for an increasing involvement of water users and the development of financially autonomous irrigation authorities at the Provincial level and Area Water Boards at the canal command level. Although, there has been a political decision to proceed with these changes, however, a very little is known regarding the details of the proposed changes and of their implementation, and their expected impact on water supply, agricultural production and sustainability of the resource base. The approach selected for implementation includes the development of selected canal command areas as pilot projects that are expected to provide information on constraints and limitations of proposed changes and lead to a successful implementation for other irrigation canal commands. It is important to note that pilot projects will impact on large areas of no less than 300,000 hectares, thus on a large number of farmers that may eventually pay for an ill-designed project or unsuitable options (Strosser 1997). The sustainability of irrigated agriculture would depend on the effective implementation of institutional reforms especially the farmers organizations at the distributary level and assigned financial autonomy of these organizations. In addition, these organisations have to be linked with input delivery channels and markets so that productivity of agriculture is enhanced and organizations have a continued role for their sustainability. The line departments have to be reorientated to change their role from authority to service. 3. Issues The Indus Basin Irrigation System today is the result of one century of supply-based 16

17 policies. Surface water is supplied to more than 16.4 million hectares or 120,000 watercourses through an extensive network of main canals and secondary canals or distributaries. The system of Warabandi and crop-based water charges is still in use, although discrepancies exist between official rules and rules in practice, for example the development of localized canal and/or tubewell water markets. The 1980s, however, have brought major changes that have stressed the inadequacy of the supply-oriented and engineering-driven interventions for projects implemented so far. The equity, efficiency and sustainability are the other issues affecting the productivity in the Indus basin. In this context, following issues are particularly important Water Scarcity The first issue relates to changes in water scarcity that have taken place within the irrigation system. It is not clear that the Warabandi system initially imposed by the British administration played a role as the demand for irrigation water was rather minimal. During the last decade, however, the pressure on water has drastically increased, with more competition for quantity and quality of irrigation water within the irrigation sector, but also from other sectors of the economy. The thrust areas related to water scarcity issues are: As a result of changes in the macro-economic environment, farmers have increased their cropping intensities from the original design figures of 50-70% to an average of 120% per year for the Indus Basin (John Mellor Associates 1994). This has led to an increasing pressure on the surface water resources (cheap freshwater), translated into a significant interference of water users into the operation of the irrigation system (Rinaudo et al. 1997). As a result of inadequate canal water supplies, but also as a response to changes in the macro-economic environment, farmers have installed a large number of private tubewells to tap groundwater resources. However, current pumping rates have already led to mining of the aquifer in several canal command areas with good groundwater quality (NESPAK 1991). In areas with poor quality groundwater, farmers still have installed tubewells and pumping leads to problems of secondary salinization and sodification (Kijne and Kuper 1995). More recently, water needs by other sectors of the economy, such as industries and municipalities, are becoming more significant, although the overall quantity used by these sectors remain marginal as compared to water use by the irrigation sector, i.e. less than 5% of total water resources (World Bank 1994). Competition over water resources between sectors has been limited to specific areas close to large cities and industrial complexes. The main issues presently at stake include competition on groundwater use (quantity), and problems of effluents and pollution of irrigation water (quality). There has been a recent recognition of the in-stream needs of the Indus River. Minimum discharges from the Indus to the sea are required to limit intrusion of seawater into the coastal area. However, little is known about the minimum flows required and how this would compete for surface water resources with the irrigation sector. 17