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Canal modernization in the Indus Basin irrigation system

Gaylord V. Skogerboe1, Zaigham Habib1, Kobkiat Pongput2,
Paul Willem Vehmeyer1 and Abdul Hakeem Khan1


An overview is given of modernization activities in the operation and design of the Indus Basin irrigation system canals, in which the International Water Management Institute (IWMI) has been involved. Hydrodynamic simulations are used to check the design and plan the operation of the Chasma right bank canal, which is under construction. The Pehur high-level canal will be the first irrigation system in Pakistan with automatic gates; the consultant's design was checked using unsteady flow hydrodynamic simulations. A modern telecommunication system is being installed in the Nara canal command area, and decision support systems are being developed for the Eastern Sadiqia and Jamrao canals. Provincial programmes on selected canal commands are underway with an area water board for the canal command and a farmers' organization for each secondary canal, with the Provincial Irrigation & Drainage Authority providing services. Thus, there is considerable change underway on canal operations in Pakistan. Water measurement and communication facilities are basic requirements for modernization. Recent research on the much-used downstream gauge ratings for canal discharge regulating structures shows that many of them require adjusted discharge ratings every few months. Thus, standard operating procedures also need to be improved in a modernization programme. The most important ingredient in modernization is organized farmers. Significantly greater benefits will accrue from a modernization programme that successfully employs a combination of institutional and technical measures.


For the past seven years, the Pakistan National Programme of IWMI has been conducting research on canal operations. In 1993, a collaborative research programme with Cemagref was initiated having a major component on decision support systems for improved canal operations. Two of the highly important tools provided by Cemagref are an unsteady flow hydrodynamic model called `simulation of irrigation canals' and an irrigation management information system which can be used by an irrigation manager to account for water distribution in the system.

The locations of the canal command areas under investigation are shown in Figure 1. The general characteristics of these canal command areas are listed in Table 1. The Pehur High-Level and the Chasma Right Bank canals are under construction. The Eastern Sadiqia canal and the Jamrao canal represent average cultivable command areas in the Indus Basin irrigation system, which covers a total of 16 million ha divided among 43 canal commands. The Lower Swat canal has the highest water duty (1.02 l/s/ha), and the Jamrao canal has the lowest, but this will increase to 0.4 l/s/ha, or slightly more, after completion of the Nara canal remodelling now underway.

Figure 1. Location of canal command areas in Pakistan undergoing modernization

Canal design

The Chasma Right Bank canal

The first experience in using the simulation irrigation system was over Stage 1 of the Chasma Right Bank canal, where it was disclosed that some portions of the canal lining needed to be raised another 75 cm in order to have sufficient freeboard. An important output of the study was the identification of operational constraints at low flow, such as a drastic drop in velocity,

which should be avoided to ensure appropriate distribution of both water and incoming sediment along the canal. At present, Stage III is under construction for a designed discharge of 138 cubic meters per second (cumecs). The complete design for the canal is now on simulation, mostly to study various operating scenarios, but also to provide the consultants with feedback regarding any required design modifications.

Table 1: General characteristics of canal command areas in Pakistan
undergoing modernization

Name of canal command


Cultivable command area, ha



Upper Swat and
Pehur High-Level


131 700




Lower Swat


53 800



Chasma Right Bank

NWFP & Punjab

228 000





172 000



Eastern Sadiqia


389 000



Nara Main


881 000





355 000



* North West Frontier Province

** This discharge rate will increase by 50 percent or more after completion of the Nara canal remodelling

Automation of the Pehur High-Level canal

The existing Upper Swat canal was designed in 1915 to divert 51 cumecs from the Swat river. Currently, the Pehur High-Level canal is under construction to convey 28 cumecs from the Tarbela reservoir on the Indus river to the tail of the Machai branch of the Upper Swat canal. The canal network of Pehur High-Level, tail of Machai Branch and the downstream Maira Branch canal has been designed using automatic downstream water level control gates. This is the first case in Pakistan of employing automatic gates in a canal.

IWMI has a contract with the Irrigation Department of the North West Frontier Province (NWFP) to provide operational support upon the commissioning of the Pehur High-Level canal. The first assignment was to use unsteady flow models to check the consultant's design (Habib, Pongput and Skogerboe, 1996). Simulation was used to check the remodelling of the Machai Branch. Another unsteady flow model, Canalman, developed at Utah State University, was used for the Pehur High-Level, tail of Machai Branch and Maira Branch canal network because this software package contains an algorithm for automatic gates. The design was subjected to a series of severe operating conditions, which showed that, in general, the system could be expected to perform well. However, IWMI also identified some of the operational complications involved in managing a combined system of upstream and downstream control, as well as the increased likelihood of sediment deposition in the Maira Branch canal. Besides the hydraulic stability provided by the automatic gates, an important feature in the consultant's design is an escape structure with a designed discharge of 29 cumecs which is located at the confluence of the Pehur High-Level canal and its Machai and Maira branches; this confluence reach acts as a regulating reservoir with an overflow escape structure. This combination of automatic downstream water level control gates and confluence reach provides excellent hydraulic stability under extreme operating conditions.

Canal operations

Discharge variability

The greatest problem faced by farmers is when there is no water during their warabandi (water turn). This is followed by the high degree of discharge variability in the canal network. Commonly, there is a daily discharge fluctuation of 20-30 percent, which on some days reaches 50 percent or more. For example, if a farmer receives only half of the normal discharge rate, then probably one-third, or less, as many bunded fields can be irrigated. Farmers are more cognizant of this problem than canal operators and irrigation managers.

Monitoring of canal discharges in Pakistan by IWMI staff, and others, has disclosed that highly significant discharge fluctuations occur, even on a daily basis. An example is shown in Figure 2 for the Fordwah branch canal at the head of the Chishtian subdivision, along with the Fordwah and Azim distributaries located at the tail of the Fordwah branch canal. The ordinate scale is the coefficient of variation, C, which is the standard deviation of a data set divided by the mean of the data set. A perfect value of C is zero. In this case, C represents the data scatter for the delivery performance ratio, which is the ratio of the actual discharge divided by the scheduled indent in order to evaluate the variability in delivering the target canal water supply. Values of C below 0.2 are considered as satisfactory, which does not occur very often in Figure 2.

One reason for such large discharge fluctuations is the lack of communication between gate operators. Each operator responds independently to changing water levels at his cross-regulator. Generally, the gate operations result in attenuated discharge fluctuations downstream. However, there are significant differences in gate operators, with some making less dramatic gate changes than others.

Figure 2: Reliability of water supplies at the head of the Chishtian subdivision (Fordwah branch) and two secondary canals - kharif 1994

The Chasma Right Bank canal

The main reason for placing the design of the Chasma Right Bank canal on simulation is to reach an agreement on how the canal will be operated when construction is completed. Stages I and II are operational, but the longest segment, Stage III, is still under construction. The main canal and the distributary head regulators will be operated by the federal Water & Power Development Authority. Two provinces are being served, NWFP and Punjab, so two provincial irrigation departments are involved. There is considerable debate, particularly among the provinces, about the day-to-day operation of that canal.

While its design is being placed on simulation, various operating scenarios are being designed. Once the design has been checked using the simulation programme in order to establish whether any modifications are required, then each of the operating scenarios will be tested and the results documented. These results will be presented to decision-makers for their consideration. It is hoped that an agreement can be reached on the most appropriate operating procedures for the Chasma Right Bank canal. There is some likelihood that the canal will later be computer-operated; the required communication facilities (radios and walky-talkies) are already in place.

Rating flow control structures

Structure calibrations

IWMI has been collaborating with the irrigation departments in Punjab and Sindh on developing a decision support system for the Fordwah and Eastern Sadiqia canals in south-eastern Punjab and the Jamrao canal in Sindh province. A basic requirement is to develop discharge ratings for all of the essential flow control structures, including headworks, cross-regulators, head regulators and outlets. Training courses have been conducted on developing discharge ratings for these structures.

During the process of calibrating so many structures, it was discovered that quite frequently the discharge ratings being used by provincial irrigation department staff resulted in discharge rates greater than those actually measured using a current meter. In fact, the discrepancy was often of 15-25 percent, sometimes more. The irrigation department ratings are based on a gauge located in the canal downstream of a flow control structure. This is helpful for the gate operator who knows what the water level on the downstream gauge should be in order to provide the appropriate discharge rate as specified by the irrigation managers. This situation led to an investigation of downstream gauge ratings.

Downstream gauge ratings

In order to investigate downstream gauge ratings, data collected by IWMI field staff was used from the Eastern Sadiqia canal in Punjab and the Jamrao canal in Sindh. In addition, data was used from the Lower Swat canal in NWFP that had been reported by the International Sedimentation Research Institute, Pakistan, which is a research unit of the federal Water & Power Development Authority.

Downstream gauge ratings are usually developed using the KD formula - Q =KD n - in which Q is the discharge rate, D a flow depth, K a coefficient, and n an exponent. The exponent n will be 5/3, as in the Manning-Strickler formula, when there is both uniform flow and the flow depth, D, represents the hydraulic radius, R. This hydraulic radius, R, is the cross-sectional flow area, A, divided by the wetted perimeter of the cross-section, P. In practice, the flow depth, D, is obtained by reading the gauge, G, but applying a gauge correction, ?G, so that :

D = G - ?G


Q = K (G - ?G) n

A unique approach was developed (Vehmeyer et al, 1998) for testing when the downstream gauge rating needs to be adjusted. Using the Manning-Strickler formula to derive the KD formula provided the example case listed in Table 2. Note that the value of the coefficient K is nearly the same for 21 and 22 October 1996, whereas the discharge measurement two months later on 29 December showed a 20 percent decrease in the coefficient K. This clearly indicates that the downstream gauge rating has changed significantly between 22 October and 29 December 1996. There were other similar examples.

Table 2. Discharge measurements at the head of the Hakra Branch canal branching off the tail of the Eastern Sadiqia canal





















R = A/P






feet (4/3)/s




Another important finding is that the variables ?G and n are linearly related, with n decreasing as ?G increases, but this is a unique relationship for each channel. After much investigation regarding the gauge correction, ?G, a procedure was derived for calculating ?G that is physically meaningful. For each current meter measurement, the gauge correction, ?G, should be obtained by subtracting the mean hydraulic depth, Dhy, from the gauge reading, G; then, average the values of ?G. The mean hydraulic depth, Dhy, is the cross-sectional flow area, A, obtained during the current meter measurement divided by the top water surface width, WT, obtained from the current meter tape measurements. Both the exponent, n, and the coefficient, K, should be considered as variables that can be derived graphically from a logarithmic plot, or by regression.

A major conclusion of this investigation (Vehmeyer et al, 1998) is that the KD formula is an appropriate technology for developing downstream gauge ratings. The discrepancies between actual discharge measurements and the downstream gauge ratings arise from the inappropriate use of this technology. There is an absolute necessity to periodically adjust the downstream gauge rating, every few months or longer, depending on changes in the channel geometry due to scouring, vegetative or aquatic growth, sediment deposition or sediment removal.

The recommended procedure is to calibrate both the flow control structure and the downstream gauge at the same time. The same current meter measurements can be used for both discharge ratings. The only additional field work is measuring water levels and gate openings at the flow control structure during each current meter measurement. The structure calibration can be expected to remain valid for a number of years. Thus, instead of periodically making a current meter measurement to adjust the downstream gauge rating, the structure calibration can be used to provide the necessary discharge rate. When the sum of the downstream gauge adjustments exceeds the original rating by about 30 percent, a new downstream gauge rating should be developed, where the structure calibration can be used to provide the discharge measurements.

Irrigation system communications

Telecommunication network for the Nara canal

A modern telecommunication system is being established for the total Nara canal command area, including the Jamrao canal command area. Besides the usual telecommunications, there will be telemetered data transmission. Some of this system is already installed, and the rest will be added in a few years. Most important, irrigation managers throughout this large canal command will have access to real-time data regarding the flow at the heads of the Nara and Jamrao canals, along with other important discharge regulating structures.

Improved communications for the Eastern Sadiqia canal

Under a four-year project scheduled to begin in 1999 with funding from the Royal Netherlands Embassy, IWMI will be working with the Punjab Irrigation Department in establishing a decision support system for the Eastern Sadiqia canal, with particular emphasis on the Hakra Branch canal that branches off its tail. About half of the subdivisions already have a base radio station, so the others will receive similar equipment. In addition, a radio communication station will be located at each cross-regulator. Many of the flow control structures in two subdivisions have already been calibrated. The unsteady flow simulation model is used to calibrate the branch canal and distributaries in the Malik subdivision and the results are placed in the IMIS programme which is being produced for use by the irrigation managers. Then, this will be done for the Haroonabad subdivision at the head of the Hakra Branch canal.

Institutional reforms

The Provincial Irrigation and Drainage Authority Act

Each of the four provincial assemblies passed a Provincial Irrigation and Drainage Authority Act in mid-1997, which converts the provincial irrigation departments into PIDAs. The act is implemented under the National Drainage Programme, whereby each province is to select one canal command for initial implementation. Besides PIDA, the act calls for the establishment of a farmer organization for each distributary (secondary canal) served by the selected canal, along with an area water board for the selected canal command, to be composed of government and farmer representatives. A study has been completed by Euroconsult for implementing the act in the Nara canal command area, which includes the Jamrao canal. Each province is completing the formulation of rules and regulations to implement this legislation.

Farmer organizations

There are very few farmer organizations at the secondary canal level in Pakistan. The On-Farm Water Management Directorate of the Punjab Agriculture Department has organized one small and one large distributaries (18 000 ha) within the Eastern Sadiqia canal command area. IWMI has organized three distributaries (6 000 ha each) in Sindh and one large distributary (18 000 ha) under the Hakra Branch of the Eastern Sadiqia canal.

When this work began in 1994-95, there were no secondary canals in Pakistan where farmers had been organized. Thus, there was no place where the farmers to be organized could be taken to gain practical insights. In fact, the vast majority of professionals associated with irrigated agriculture were highly sceptical about their ability to organize farmers. But an important lesson that has been learned is that farmers do want to be organized. In order to achieve equitable water distribution, 132 farmer leaders have been taught how to measure water, much to their own amazement. This has created much transparency. The objective is to achieve equitable water distribution to each tertiary channel served by the secondary canal.

Organizing farmers on a secondary canal is not sufficient. Farmers should be organized on every secondary canal in the canal command area. Under the proposed Dutch funding, due to begin in 1999, the On-Farm Water Management Directorate will organize the remaining distributaries under the Hakra Branch canal. The farmers under each distributary would be organized into a Water User Federation. Each federation would enter into a joint management agreement with the local PIDA. IWMI will provide support to the On-Farm Water Management Directorate in this endeavour.

The Eastern Sadiqia Canal Water Board

Under the proposed Dutch funding, the water user federations under the Hakra Branch canal would be federated into an informal organization that would function like a water board. The details for the functioning of this federation of federations would be formulated during the course of the project by the Punjab Irrigation and Drainage Authority with assistance from the On-Farm Water Management Directorate and IWMI. The intent is to learn from this model so that the lessons learned are useful for the selected canal command in each province for implementing the PIDA Act.


Water measurement is a basic requirement for improving the operation of any irrigation system. In fact, developing and updating the discharge rating for each essential flow control structure in a system should be standard operating procedure.

Proper communication facilities are one of the more cost-effective measures for improving the performance of an irrigation system. As a system becomes modernized, the transmission of real-time data becomes more important.

Water measurement and communication facilities are basic ingredients required for any irrigation system modernization programme. Modernization is undertaken to enhance service to the beneficiaries and increase the sustainability of agricultural productivity. The most effective manner for achieving these objectives is for irrigation agencies to provide technical assistance as a service to farmer organizations. The technical feasibility of physical or operational interventions to improve the system must be analysed before their implementation, and proper consideration given to the system constraints. Identifying appropriate ways of operating the system is necessary for a reliable and equitable distribution of water in the existing, as well as the planned, irrigation systems. This becomes even more important in modern complex irrigation systems like the Chasma Righ Bank and Pehur High-Level canals. For these kinds of systems, operating scenarios must be carefully established.

The most important component, however, is organized farmers. Once organized in an effective manner, farmers will demand equitable water distribution. In fact, the organization cannot be sustained unless this objective is achieved. Also, they will have a keen interest in reducing discharge variability. The main disadvantage of organized farmers is that they will no longer pay irrigation field staff and officials for illegally receiving water. The main advantage is that significant increases in agricultural productivity can be expected.

A technical approach to modernization will likely be cost-effective, but significantly greater benefits will accrue from successfully employing a combination of institutional and technical measures.


Habib, Zaigham; Kobkiat Pongput & Gaylord V. Skogerboe. 1996. Unsteady flow simulation of the designed Pehur high-level canal and proposed remodeling of Machai and Maira branch canals, North West Frontier Province, Pakistan. IIMI, Pakistan National Programme, Report No R-20, December, 147 pp

Habib, Zaigham & Marcel Kuper. 1998. Performance assessment of the water regulation and distribution system in the Chishtian subdivision at the main and secondary canal levels. IIMI, Pakistan National Programme, Report No R-59, July, 110 pp

Vehmeyer, Paul Willem, Raza-ur-Rehman Abbasi, Mushtaq A. Khan, Abdul Hakeem Khan & Gaylord V. Skogerboe. 1998. Methodologies for developing downstream gauge ratings for operating canal discharge regulating structures. IIMI, Pakistan National Programme , Report No R-48, April, 112 pp

1 Director, Systems Analyst, Associate Expert (Hydraulics) and Senior Field Research Engineer, respectively, Pakistan National Programme, International Water Management Institute.

2 Professor, Department of Water Resources Engineering, Kasetsart University, Bangkok.

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