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Producing more crop yield with a lesser amount of water is a challenge for irrigated agriculture across the world. Agricultural products contribute a lot towards GDP of various regions worldwide. Irrigated agriculture mainly depends upon the performance of irrigation system. It uses more than 65% of fresh-water. Therefore improving irrigation efficiency is the most important step towards addressing human water needs. Madramootoo and Fyles, 2010, Molden et al 2010, Lecina et al 2010 and Namara et al 2010) have made investigations regarding improvement of the irrigation water productivity. Inequitable water supply has been looked into more deeply by Brown (2011). Poddar et al. (2011) Hornidge et al. (2011), Ricks and Arif (2012), Yakubov (2012) and Ghazouani et al. (2012) have investigated problems associated with the irrigation systems and and possible improvement in management of irrigation.
Similar efforts are being made in Pakistan also (see Shakir and Maqbool 2010, Shakir et al. 2010
and Ghumman et al. 2012). Irrigation in Pakistan has a long history. Most of the systems of
irrigation in the country are old. There is over supply of water in the season of low water
requirements in KPK Province of Pakistan. Advancements in knowledge recommends well-
organized irrigation providing optimal water quantities. This needs good management and optimal
operational strategies. The discharge should be varried according to the demands. Simulations
through computer models are extremely helpful for such situations. Several attempts have been
made to address the problem of computer simulations (see for example Ghumman et al 2009,
Ghumman et al 2010, Tariq and Latif 2010 and Tariq 2010). Various problems of irrigation in
Pakistan have been studied in these papers but the task taken in this paper for exploring the best
possible use of irrigation-water in an extremely important distributary like Kalu Khan will
definitely be useful for the managers, planners and engineers in KPK.
DESCRIPTION OF THE AREA UNDER STUDY
Figure 1 shows the study area. It lies in KPK Province of Pakistan. The main canal takes water
from Amandara Headworks on Swat River. The main canal has two branch canals namely Abazai
and Machai. This main irrigation system underwent re-modeling in mid 1990s, when the water-
allowance was changed from 0.35 litres/second/hactare to 0.7 litres/second/hactare (3.5 mm/day to
6 mm/day), which is close to the maximum irrigation requirements. The problems of water
shortages in winter in the tail sections of the system were addressed through the construction of Pehur High Level Canal (PHLC) which is fed by Indus River at Tarbela. Maira branch and PHLC both are are important canals with moderen devices at every 5 kilometers to regulate discharge. Kalu Khan canal is upstream of Machai-PHLC confluence. Its design discharge is 2.27 m3/s. It has 20 operational outlets and is about 17 km long, (Government of NWFP. 1992).
Figure-01: Map of Study Area and line diagram of Kalu Khan Distributary
The one dimensional-flow in branching canal system for unsteady conditions is expressed by the following two governing equations (see for details Strelkoff 1969).
Equation of continuity:
+ = 0 (1)
Equation of motion:
âˆ‚ Q 1 âˆ‚ ( Q / A ) âˆ‚ y
+ + gA = gAS
âˆ‚ t Ag âˆ‚ x âˆ‚ x
âˆ’ gAS (2)
Here Q = flow (m3/s), A= flow area, g = gravitational-acceleration; y = flow-depth, t = time, x
=distance in the direction of flow, So represents channel-bed slope, Sf=slope of the energy line.
Additional equation is required to estimate Sf as given below:
Manning's equation S f =
(4 / 3)
In this equation n is a constant showing frictional effects, R= ratio of flow area to the wetted
perimeter. The constant n is very important. Its value must be identified for the given canal.
Simulation of Irrigation Canals (SIC)
The SIC can simulate the hydraulic behavior of most of irrigation systems. The SIC model has
been developed by the Irrigation Division of Cemagref, Montpellier, France (Tariq 2010). SIC can
perform simulation for flow in a system of canals and can be used to investigate various aspects of
canal irrigation. The model is based on one dimensional equations of Saint-Venant as described
above. The model has three parts: a topographical unit to generate the topography and topology of
the irrigation system, and two separate computational units for steady and unsteady flow.
THE PREVAILNG CONDITIONS
Figure 2 shows the measured water-supply of canal and actual crop-water requirements. During the study period, Kalu Khan Distributary was never observed to be operated at full supply. The maximum discharge ever observed was 70% of the design discharge. There was over-supply only in March and July as compared to demand (figure 2). During the period from May to June and September to October, there was under supply as compared to the demand.
1-Jan 1-Feb 1-Mar 1-Apr 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct 1-Nov 1-Dec
Figure 2: Supply and irrigation requirements of Kalu Khan Distributary
A comparison of the supply and irrigation requirements of three sample outlets of Kalu Khan
Distributary is presented in figure 3. The peak irrigation requirements were in May, June and
September. Outlet 2400/L received around 4 mm/day, which was far less than the design (6
mm/day) and was insufficient to meet the irrigation-requirements in May-June. There was
however, over supply to outlet 2400/L in July and October to December. Outlet 34500/R received
around 3 mm/day. The outlet remained water deficient in May, June and September, which are the
peak demand months. Outlet 57132/L received enough water to meet the peak crop-water
requirements in May, June and September. There was over supply in July, August and October to
During the data collection tours of the study area were arranged time to time. In these tours it was
noticed that during the season of low water requirements by the crops the water-supply from canal
was higher than the requirements. There was waste of irrigation-water. An interesting situation was
observed. The farmers did allow water into their watercourses in such situations. It was thrown
into a natural or artificial drain passing close to the water the watercourse. On the other hand there
was short-supply during the peak season of crop-water-requirements. It definitely was affecting the yield per hectare of the command area of the canal. Water logging was also being caused by the wasted water.
These real conditions of the canal observed during the study forced to make simulations so that some solution may be sought for saving precious water during over-supply and providing sufficient supply during the peak season.
9 Design (57132-L), (34500-L) & (2400-L) Gross Requirement
8 Supply (57132-L) Supply (34500-L)
7 Supply (2400-L)
3/4/04 4/23/04 6/12/04 8/1/04 9/20/04 11/9/04 12/29/04 2/17/05
Figure 3: Supply and irrigation requirements of three sample outlets of Kalu Khan Distributary.
CALIBRATION AND VALIDATION OF MODEL
Before making simulations, it is necessary to calibrate and validate the model. The model
calibration was done by minimizing the error between the observed water level profiles with the
water level profiles simulated by the model, to determine suitable values of Manning's 'n', for each
canal-section. The values of Manning's roughness constant determined by calibration for different
reaches of the Kalu Khan Distributary have been found as 0.018 for lined-reaches and 0.023 for
The validation of Kalu Khan Distributary was made for discharge values of 1.75 m3/s and 1.19
cumecs. This was the most frequently available discharge in the canal. During the study period
1.75 m3/s was the maximum discharge drawn by the canal. The validation results are presented in figure 4, which show a good calibration of the model for Kalu Khan Distributary. The model efficiency (Khan (2006)) for validation was obtained as 96%. The parameter (âˆ‘(Hm-Hc)/hm)2 resulted to as 0.235, where Hm and Hc are measured and calculated water levels.
1.75 Cumecs (Measured) 1.75 Cumecs (Simulated) 1.19 Cumecs (Measured) 1.19 Cumecs (Simulated)
732 1943 3002 4040 7755 9238 10518 11646 15488 17418 18353
Figure 4: Comparison of real(observed) and calculated(simulated) water-depths in model-
For optimal water supply variation in discharge was required according to the crop-water-
requirements. To check whether it was possible to run the Kalu Khan Distributary at lower flows during the season of lower crop-water- requirements, its operations for varied flows were simulated using SIC model. The following four conditions of canal flow were modeled.
A The flow required for peak crop-water-requirement. It is also called the design flow or full supply flow
B Eighty percent of the flow at option A.
C Seventy percent of the flow at option A. This option is related to lowest possible level of operation for the outlet- proportionality condition.
D) Fifty percent of the flow at option A.
The criterion of delivery performance ratio (DPR) was used for performance assessment. DPR is
defined as the ratio of the real flow of outlet to the targeted flow (see the reference Murray-Rust
and Snellen 1993). To evaluate the performance of outlets of the canal, the criterion used by the
Departments of Irrigation in Pakistan was selected. According to this criterion the outlets of a
canal are said to be operating satisfactorily if these are drawing flows within plus/minus1ten
percent of their allocated flows (see Govt. of NWFP/KPK, 1992). If the delivery performance ratio
(DPR) is 1.0 then the working of an outlet is obviously ideal one. The other performance level of
Â±30% was used (see Murray-Rust and Halsema 1998), below which the performance of an outlet was considered unacceptable.
RESULTS AND DISCUSSION
The performance of Kalu Khan Distributary assessed for four flow conditions of 100%, 80%, 70%
and 50% of design is shown in figure 5. Under the Â±10% criteria only 5, 4, 3 and 4 outlets were
within the acceptable range. For the criteria of Â±30%, 11 outlets were found to be within the range
under all the four discharges. The performance of rest of the outlets was not up to the mark. There
are several reasons for the bad performance of these outlets, which include restrictions imposed on
the outlets by the downstream conditions, type of outlet, and dimensions of the outlets. Outlet 1L
has a very low (about 0.5) DPR. It is due to restriction to flow due to a road culvert downstream of
the outlet, which was modeled for a low value of the discharge coefficient. The DPR values of
outlets 5L, 6R, 8R, 13L and 14R are very high (about 2 to 2.5). They were constructed as open
flumes, although they should have been constructed as AOSM structures. Outlets 9L, 16R and 23R
were constructed as AOSMs and their DPR is very low. These should have been open flume
outlets. Outlet 10L was designed as a crump weir but has been constructed as an undershoot gate
with no crest. This outlet requires provision of a crest. Outlet 19R has been designed and
constructed as a crump weir. Its DPR is high and requires adjustment in its width.
2.5 100% 80% 70% 50%
Figure 5: Performance of Kalu Khan Distributary under different discharge conditions.
Existing conditions of a secondary level canal in Pakistan have been studied. Its performance is not
satisfactory under existing situation. The usefulness of simulations by SIC in testing the
performance of canals for different discharge conditions is highlighted. It is concluded that
performance of the canal cannot be improved with existing configuration even with discharge variations. The existing delivery performance ratio is upto 2.5 instead of required DPR of 1.0, showing very bad performance of the canal. A trend of over drawing (more than 100% in some cases) by the head outlets is observed in the secondary canal. The performance is the best one between eighty to hundred percent of the full-supply flow.
There are many options to improve the performance of the canal. One possible option is to make modifications in the outlet-dimensions. An optimization of outlet dimensions can be done using optimization techniques or at least using hit and trial method with SIC model. The model SIC may be run again and again by changing the dimensions of outlets every time so that the best possible dimensions are achieved.
The other option is to get proper lining of the whole length of the canal.
The staffs of the Water Management Institute (IWMI) Pakistan, Meteorological Station Mardan (NWFP) and Irrigation Department Government of NWFP deserve appreciations for their help in gathering. Support from Higher Education Commission of Pakistan and Engineering University Taxila is also acknowledged.