Water Resour Manage (2010) 24:3085–3099 DOI 10.1007/s11269-010-9596-x
Improving Operational Performance of Farmers Managed Distributary Canal using SIC Hydraulic Model Javaid A. Tariq · Muhammad Latif
Received: 1 September 2009 / Accepted: 18 January 2010 / Published online: 28 January 2010 © Springer Science+Business Media B.V. 2010
Abstract Operation of a secondary canal was recently transferred to the farmers’ organization (FO) under irrigation management transfer (IMT) programme. After modernization of Upper Swat Canal (USC) irrigation system, the water allowance was increased to operate the irrigation system more in demand responsive mode. The study of the existing operation of the canal revealed that most of the time the irrigation supplies exceed the demand and the farmers either over irrigate their fields or waste precious irrigation water. Operation and management aspect of the irrigation system play a pivotal role in overall water management practices. SIC hydrodynamic model was employed to evaluate the operational performance of the distributary. Different operational scenarios were investigated and quantified based on fixed frequency operation. Based on these results it is suggested to operate the distributary at 80–90% of the design discharge during May to July, and 75–90% of the design discharge from August to April to reduce water losses due to high water allowance. Keywords Operation · Irrigation · Modeling · Simulation of irrigation canal (SIC) hydraulic model · Irrigation management transfer
1 Introduction Efficient and effective operation of irrigation facilities is a key to achieving sustainability in irrigated agriculture. Operations are routine actions taken to minimize the impact of perturbations by maintaining steady or quasi-steady state water profiles in the system and to prevent overtopping at peak discharges (Renault and Makin 1998). Since the past few decades irrigation researchers have been emphasizing the need for
J. A. Tariq (B) · M. Latif Centre of Excellence in Water Resources Engineering, University of Engineering and Technology, Lahore, Pakistan e-mail:
[email protected]
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improving the operation of irrigation systems and establishing farmers’ organizations for effective management of the irrigation systems. Wade and Chambers (1980) have emphasized the need for treating operation of the canal as a separate professional task. Chamber (1988) and Bottrall (1981) designated management of main irrigation system as a blind spot and considered the delivery of appropriate and reliable supply at the outlet as pre-condition for proper utilization of irrigation water. Inadequate operation and maintenance have significantly reduced the benefits of large scale public irrigation systems (Svendsen et al. 1983). Researchers (Lozano et al. 2010; Loof et al. 1994; Plusquelle 2002; and Zimbelman 1987) believe that greatest potential for increased agricultural production lies in improving operation of irrigation systems. Mangers of the irrigation systems have to make daily decisions on how to allocate available water supply to meet the crop water demand. Hydraulic modeling is an appropriate tool to understand and diagnose hydraulic behaviour of the irrigation systems. A properly calibrated and validated model can be utilized to analyze and improve the operational performance of an irrigation system. During the last decade, considerable research and efforts have been made to analyze the complex situations using simulation models for improving the operation of the irrigation systems such as Schuurmans and Maherani (1991), Godaliyadda et al. (1999), Mainuddin et al. (2000), Mishra et al. (2001), Kumar et al. (2002), Shahrokhnia and Javan (2005), Habib et al. (1996, 1999), Waijjen et al. (1997), and others. Turral et al. (2002) used steady state model, IMSOP to evaluate alternative strategies and improved operational regimes to offer better service to farmers in pumped irrigation systems in the Red River Delta and in surface systems in southern Vietnam. Bievre et al. (2003) applied hydrodynamic model to simulate abrupt discharge changes and their travel times along small irrigation canals. Filling and emptying of the canal were also analyzed and it was concluded that significant water savings can be achieved by reducing night-time water supplies in medium sized canal networks. The feasibility of closing distributary canals at night was investigated by Ghumman et al. (2009) in recently modernized gravity irrigation system and it was concluded that the feasibility of night-time canal closure depends on the rate of filling and emptying the canal each day as well as the time required to meet full irrigation demand during the day. Whereas de Vries and Arif (2006) concluded that if the canals are long and travel time is relatively more, then night-time canal closure may not be feasible as it will not allow effective day-time supply due to longer time taken to re-establish the design water levels.
2 Description the Study Area 2.1 Upper Swat Canal (USC) The Upper Swat Canal (USC) was commissioned in 1914 and it irrigates a large proportion of the North West Frontier Province (NWFP). The Upper Swat Canal (USC) takes water from Swat River through Amandara headwork that was originally designed for a discharge of 68.6 m3 s−1 (2,420 cusecs) to irrigate an area of 127,500 ha. The canal is operated under upstream control, in which adjustments to canal discharge are made at the head of the main canal system. The canal, after traversing
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the narrow ridge of Malakand hills through the Benton Tunnel, eventually bifurcates at Dargai into two branches: Machai on left, and Abazai at the right side. About 75 km length of the Upper Swat Canal (RD 0+000 to RD 242+000) was remodeled under the Swabi Salanity Control and Reclamation Project (Swabi SCARP Project) in 1998, while the remaining portion of about 50 km was remodeled under the Pehur High Level Canal (PHLC) Project in 2002 (Fig. 1).
Fig. 1 Upper swat canal and Pehur high level canal network
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After construction of the Benton Tunnel in 1914, it was realized that its discharge capacity was not more than 51 m3 s−1 (1,800 cusecs) due to its unlined and rough surface. As a result of this constraint, the authorized full supply discharge of the canal was fixed at 51 m3 s−1 (1,800 cusecs) and the Cultivable Command Area (CCA) reduced to 111,700 ha (276,000 acres). To bridge the gap of water shortages due to Benton tunnel, the construction of another tunnel as an auxiliary tunnel was realized. The auxiliary tunnel was designed and constructed for a discharge of 51 m3 s−1 (1,800 cusecs) and it can pass on a discharge up to 60 m3 s−1 (2,100 cusecs). As a result of the construction of this tunnel the capacity of the Upper Swat Canal was also increased to 100 m3 s−1 (3,200 cusecs). The design capacity of the two branches of the canal i.e. Machai and Abazai has been remodeled to pass the increased flow when Swabi SCARP Project was constructed in 1998. Water allowance was increased from 0.39 to 0.63 L s−1 ha−1 due to increased discharge of the canal. 2.2 Pehur High Level Canal (PHLC) Pehur High Level Canal was constructed to convey irrigation water from Gandaf Tunnel to Machai branch of the Upper Swat Canal at (RD 242+000) via Baja Tunnel (Fig. 1). It is 26.2 km long with majority of its length as lined channel. It crosses some major hill torrents through inverted siphons. The canal is designed and constructed with a capacity of 28.30 m3 s−1 (1,000 cusecs) at the upstream. This canal receives water supply from two independent sources: the Swat River and Tarbela reservoir during different time periods. From April to July, there is not enough water in the Tarbela reservoir and the USC receives water from the Swat River. During rest of the year, water is supplied from the Tarbela reservoir. The PHLC supplements water supply to Machai branch at tail reaches of the USC. This has resulted in improving and extending irrigation facilities in Swabi district. The tail end of the Upper Swat Canal and Machai branch have been remodeled by increasing their capacities from 0.39 to 0.77 L s−1 ha−1 to bridge the gap between supply and demand while the annual cropping intensity has been increased from 120% to 185%. The system remodeled under the PHLC Project uses automatic downstream control gates (AVIS and AVIO type)1 installed at about 5 km intervals. These gates are sensitive to water level and open or close automatically when level falls below or rises above a fixed level. 2.3 Chowki Distributary The Chowki distributary offtakes from Maira branch canal. It is managed and operated by the Farmers Organization (FO) after the irrigation management transfer
1 The
downstream controlled system is normally equipped with hydro-mechanical gates, such as AVIS and AVIO gates. The essential dierence between the AVIS and AVIO gates is that AVIS operates at a free surface flow in upstream canal section, while the AVIO gate closes as an orifice. The names AVIS and AVIO have French origin: AV are the first two letters of the word ‘AVAL’, which mean downstream, and S for the first word of French word ‘surface’. Also the name AVIO, letter S in AVIS is replaced by O, which is the first letter of French word ‘Orifice’ to get the name AVIO (Ankum 2004).
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(IMT) in Swat Canal Area Water Board (SCAWB). The FO is responsible for the irrigation water distribution, maintenance of the irrigation channels and collection of water charges from the farmers. Chowki Distributary has cultivable command area of 4,161 ha having 1,485 beneficiaries. The system has a total of 19 direct outlets and nine outlets offtake from two minor.2 The design discharge of the Chowki distributary is 3.07 m3 s−1 . Approximately 44% of the farmers have farm size ≤1 ha. The maximum landholding is 20 ha and the average farm size is 2 ha. There are equal numbers of tenants and the land owners. The farmers are growing a number of crops both in summer and winter seasons. The major crops are maize, tobacco, wheat, sugar beet, alfalfa and sugarcane. The annual cropping intensity is 175%.
3 Description of SIC Model 3.1 Structure of the Model The SIC model can be divided into three main units. Unit I is used to create the topography and geometry files to be used by the computational program of Units II and III. Unit I allows to input and verify data obtained from the topographical survey of a canal. Unit II is used to carry out steady flow computations. It allows analyzing the water profile for any combination of discharges or settings of the offtakes and cross structures. This unit also allows computing the required settings at offtakes and adjustable cross structures in order to satisfy a given distribution plan and to maintain target full supply depth upstream of the cross structures. Unit III processes the unsteady flow computation. This allows the user to test the various scenarios of water demand schedules and operations at the control structures. The SIC model has been tested for computational accuracy using benchmarks developed by American Society of Civil Engineers (Malaterre and Baume 1997).
4 Solution Algorithms 4.1 Differential Equation for Water Surface Profile Steady flow computations allow analyzing the water profile for any combination of discharges. With the canal being divided into homogeneous zones (reaches), the problem is reduced to calculating the water surface profiles under subcritical and steady flow condition in a reach. The classic hypothesis of unidimentional hydraulics in canal i.e. flow direction is sufficiently rectilinear, so that free surface could be considered sufficiently horizontal in a cross section, traverse velocities are negligible, pressure distribution is hydrostatic and friction losses are taken into account through Manning–Strickler coefficient. To solve the equation, upstream
2 In
Pakistan secondary irrigation canal is called a ‘distributary’. A ‘minor’ is a smaller secondary canal.
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discharge and downstream water surface elevation are needed to be defined after which computations will commence from the tail of the channel. The equation of water surface profile in a reach can be written as: dH qQ (1) = −S f + (k − 1) ∗ dx g A2 and
Sf =
n2 Q2 A2 R4/3
(2)
where g n R A H q Sf Q
gravitational constant = 9.81 ms−2 Manning coefficient (m−1/3 s) hydraulic radius (m) cross section area (m2 ) total head (m) lateral inflow (q > 0, k = 0) or outflow (q < 0, k = 1), (m3 s−1 ) linear head losses (m2/3 s−1 ) discharge (m3 s−1 )
In addition lateral flow and hydraulic roughness coefficient along the canal should be known. As the equation has an analytical solution in the general case, it is discretized in order to obtain numerical solution. Knowing the upstream discharges and the downstream water elevations, the water surface profile is integrated step-bystep starting from downstream end. Integrating the equation between two sections i and j gives: Vj ΔXij S fi + S fj Vi H j − Hi − kq ∗ Δxij = 0 − (3) + 2g Aj Ai 2 Hi (Z i ) = H j + ΔH (Z i ) = 0
(4)
If solution does exist, one has to numerically solve an equation of the form f (Z i ) = 0 for which Newton method (Baume et al. 2005) is used. Unit III is used to carry out unsteady flow computations. It allows testing various distributions plans at the offtakes, and operations of main sluices and cross structures (manual or automatic). SIC package is based on one-dimensional Saint-Venant’s partial differential equations (Chow 1959; Chaudhry 2007) that describe flow in open channels. Two equations are needed to describe unsteady flow in open channels, which are based on the law of conservation of mass (continuity equation) and momentum. The equations are: ∂A ∂Q + =q ∂t ∂x ∂ ∂Q + ∂t ∂x
Q2 A
∂z + g.A ∂x
(5)
= − (g A) ∗ S f + k ∗ (qV)
(6)
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To solve the above equations, the boundary conditions are the hydrographs at the upstream nodes of the reaches and the rating curve at the downstream node of the model. The initial condition is the water surface profile resulting from the steady flow computation. Saint Venant’s equation is solved numerically by discretizing: the partial derivatives are replaced by finite differences. It uses the classical implicit Preissmann scheme (Chaudhry 2007; Baume et al. 2005; Cunge et al. 1980). This schemes is implicient because the values of the variable at unknown time steps also appear in the expression containing the spatial partial derivatives. The implicit coefficient is set to 0.6.
5 Data Collection for Model Setup Topographic survey of the Chowki distributary was conducted during 2006–2007. Cross sections (bed width and elevation of the banks) of the canal were measured approximately at every 50 m. Reduced levels were obtained in relation to datum at head of the Chowki distributary. Twenty-seven inline cross structures (crump’s weirs) have been built to control the discharge. Dimensions (width and crest elevation) of the flow control structures were measured and inserted in the model. Throat width, sill elevation of the offtakes were physically measured and inserted as node in the SIC model. Downstream boundary condition of Chowki distributary was based on actual water levels and discharge rating curves. The inflow to the network was considered as initial value and it was taken positive whereas outflow on the offtake nodal points was taken negative. The head regulator of the distributary and all the offtakes were calibrated through the use of painted reference marks on the upstream and downstream faces of the structures. Readings of the difference between the water level and reference marks were converted to actual heads. A rating curve was developed by area–velocity method using current meter. Discharges were calculated from the rating curve for the daily measured water levels.
6 Calibration and Validation of the Model Model calibration involves checking the model results with the observed data and adjusting the parameters until the model results fall within acceptable range of accuracy. Calibration of the model was accomplished by matching the computed and measured water levels and discharges of the offtakes for the same flow conditions at the head of distributary. The data used for calibration of the model in steady state condition consist of a set of water levels at crest of the bifurcators, trifurcators and open flumes for 100%, 80%, 70% and 60% of the design discharge. At Chowki distributary intensive measurements were taken for calibration and validation of the model on 11th to 30th May, 4th and 6th June, 12th and 26th September, 2007. After calibration of the model for typical situations observed in the field, the model was validated with another data set to recheck the results simulated by the model. The Manning’s roughness coefficient and discharged coefficient were adjusted to obtain
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the required water level and discharge. The simulated water levels matched closely with the measured water levels at full supply discharge as shown in Fig. 2. To further check the calibration and validity of the model Nash–Sutcliffe Efficiency Coefficient (NSEC) and Percent bias (PBIAS) were calculated. The Nash–Sutcliffe Efficiency Coefficient (NSEC) is a dimensionless indicator and it has been recommended by ASCE (1993). NSEC values between 0 and 1.0 are generally viewed as acceptable levels of performance, whereas values ≤0.0 indicate unacceptable performance. It is calculated as:
NSEC = 1 −
⎧ ⎫ n ⎪ ⎪ (Qto − Qts )2 ⎪ ⎪ ⎨ ⎬ i=1
(7)
n ⎪ ⎪ ⎪ ⎩ (Qto − Qo )2 ⎪ ⎭ i=1
where Qt0 are observed discharges, and Qts are simulated discharges at time t, Q0 is mean of the observed data and n is total number of observations. The percent bias (PBIAS) measures the average tendency of the simulated data to be larger or smaller than their observed counterparts. The optimal value of PBIAS is zero and lower values indicate better simulation. A positive value indicates a tendency of the model for underestimation while negative values indicate overestimation (Moriasi et al. 2007). PBIS is determined as:
PBI S =
⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩
n
100 ×
t=1
Qto − n t=1
n t=1
⎫ ⎪ Qts ⎪ ⎬ (8)
⎪ ⎪ ⎭
Qto
Calculated values of NSEC and PBIS for different discharge levels are presented in Table 1, for calibration and validation of the model. It is evident from the table that
360.00 350.00
Elevation (m)
340.00 330.00 320.00 310.00 300.00 290.00 0
10
20
30
40
50
60
70
Distance along the Chowki Distributary from Head Regulator - Hundrad (m) FSL Design (m)
FSL Simulated (m)
Fig. 2 Comparison of observed and predicted water levels
Bed Level
80
Improving Operational Performance of Distributary Canal Table 1 Calculated values of statistical parameters for calibration and validation of the model
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Calibration Qd (%) NSEC
PBIS
Validation Qd (%) NSEC
PBIS
100 80 70
−0.10 −0.13 −0.15
90 85 60
−0.11 −0.13 −0.17
0.96 0.93 0.91
0.95 0.94 0.89
the values of both the indicators for different discharge levels are small and fall within acceptable range as discussed earlier. Therefore, the model is considered calibrated and validated. 6.1 Operational Performance The operational performance was evaluated using volume indicator, incorporated in SIC model, with a view to evaluate the water delivery efficiency at the offtakes. This allows integration of the information on water delivery, either at a single offtake or at all the offtakes. Baume et al. (2005) have suggested the following performance indicators to assess the effectiveness of the delivery schedules: Ef fective Delivery Effective discharge (Q EF ) at an offtakes is derived from the delivered discharge (Q D ) and from the target discharge (QT )using the following constraints given in Eq. 9. The effective volume depends on two coefficients, w and x. The values used in simulation for w and x were 15% and 35% respectively: ⎫ w x .Q D ≤ Q S ≤ 1 + .Q D ⇒ Q EF = Q S ⎪ If 1− ⎪ ⎪ ⎪ 100 100 ⎪ ⎬ w I f QD < 1 − .Q D ⇒ Q EF = 0 (9) ⎪ 100 ⎪ ⎪ ⎪ x x ⎪ ⎭ I f QD > 1 + .Q D ⇒ Q EF = 1 + .Q D 100 100 The total effective volume (V EF ) over a period of time T is given by Eq. 10 as: V EF =
T
Q EF dt
(10)
0
Adequacy This indicator measures the performance of the scheme in terms of adequacy for offtakes between the head inlet and the target delivery point. It measures how well effective volume in the schedule matches with the downstream requirements. Adequacy for an offtake is expressed as the ratio of effective volume (V EF ) to targeted volume (V D ) as: 1 T V EF Adequacy = = (11) Q EF dt VD VD 0 Operational Ef f iciency (Eop ) It is the ratio of effective volume (V EF ) at the delivery point within the targeted period of time to the volume delivered from the main supply (Vs). It is the measure of the delivery system ability to supply water according to schedule. When the effective volume (V EF ) exceeds the target volume (V D ), the volume received in excess of the intended volume is considered to be lost. The
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assessment criteria adopted in this study is: 0.80 ≤ Eop ≤ 1.00 good; 0.70 ≤ Eop ≤ 0.79 satisfactory and Eop ≤ 0.70 poor. The effective volume (V EF ) is computed with restriction to the expected period of delivery as: 1 T2 V EF Q EF dt = (12) Eop = VS V S T1 Where T1 is expected arrival of wave and T2 is expected finish of the wave. Delivery Performance Ratio (DPR) Is defined as the ratio of the actual discharge and design discharge and specifies to what extend the intended water supply is actually delivered. The DPR in operation of irrigation system allows for instantaneous checking of whether discharges are more or less than the design discharge. The operational objective of irrigation system is to as efficiently and effectively as possible provides the equitable distribution of available irrigation supplies to all the stakeholders. The nominal range of the proportionality is 70% to 110% of the design discharge. At low flows, the proportionality becomes more difficult to maintain and misappropriation of water to offtakes increases, secondly at low flows small channels causes increased sedimentation. DPR is calculated as: VS V EF Vs DPR = = × (13) VD VD V EF Based on preceding discussion on operation philosophy of irrigation system in Pakistan, it is logical to accept the minimum lower DPR of 0.7 and upper limit above 1.10 is considered as poor performance. The assessment criteria adopted in this study is: 0.90 ≤DPR ≤ 1.10 good; 0.70 ≤DPR ≤ 0.89 satisfactory, and DPR ≤ 0.70 poor.
7 Results and Discussion 7.1 Current Operation of the Distributary Operation of the distributary regulates the whole delivery system and it plays keys role in farming operations. Chowki Distributary was operated on rule of thumb and haphazardly without giving due care to the irrigation demand even after IMT and modernization. Figure 3 indicates that distributary head regulator is not operated in response to water demand. During the rainfall events and in period of low demand, i.e. middle of March–April and in November, the farmers close completely or partially their outlets, which cause overtopping at the tail as there is no escape in the Chowki distributary, and the only choice is to reduce discharge at its head. The main canal system may be closed when there is heavy rain. Previously, former Provincial Irrigation Department (PID) used to close the entire system from the headwork, if rainfall of 70–100 mm or more occurs. Unilateral decision to shut the system at headwork in single order is easy than to operate the escapes at main canal and distributaries head regulators. Same operation procedure for the headwork is followed by establishment of the Area Water Board and Regulation Cell. As long as irrigation supply exceeds the demand, and water is in abundance, the equity and proportionality does not create any social problem after the IMT under the FO operated irrigation system.
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3.5 3.0
3 -1
Discahrge (m s )
2.5 Design Discharge
2.0 1.5 1.0 Supplied Discharges
Demand Discharges
0.5
31-Dec
3-Dec
17-Dec
5-Nov
19-Nov
8-Oct
22-Oct
24-Sep
10-Sep
27-Aug
30-Jul
13-Aug
2-Jul
16-Jul
4-Jun
18-Jun
7-May
21-May
9-Apr
23-Apr
26-Mar
12-Mar
26-Feb
29-Jan
12-Feb
1-Jan
15-Jan
0.0
Fig. 3 Demand and supply pattern of Chowki distributary
Irrigation delivery patterns (Fig. 4) reveal that irrigation supplies are unrelated to crop evapotranspiration. The irrigation system is closed for annual maintenance in the beginning of the year. From 15th March to 20th August, irrigation supplies exceed the evapotranspiration (irrigation demand). Evapotranspiration of crops was calculated based on actual cropped area (Latif and Tariq 2008). From third decade of August to last decade of September water supplies were close to the
-1
Irrigation Deliveries (mm day per CCA)
14.0 12.0
Irrigation Deliveries 10.0
ETc 8.0 6.0 4.0 2.0
Fig. 4 Irrigation water deliveries and ETc of Chowki distributary
Dec II
Nov III
Nov I
Oct II
Sept III
Sept I
Aug II
July III
July I
June II
May III
May I
April II
March III
March I
Feb II
Jan III
Jan I
0.0
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evapotranspiration. However, after September evapotranspiration fell below 2 mm day−1 , while water deliveries were maintained at their normal high level. The analysis of current operation reveals that Chowki distributary is being operated on conventional operation approach i.e. upstream control and a constant downstream depth operational rule. It essentially combines demand-based needs with supply-based operation. Operational decision-making is based on local experience of the farmers’ organization (FO). The operators of Swat Canal Area Water Board (SCAWB) regulate head regulator of the distributary on the request of the farmers’ organization (FO). However, major drawback of this method is unavoidable discrepancy between the required and actual delivered flows that aggravates the water distribution at tertiary level thereby wasting large amount of irrigation water. Most of the time, the distributary was not operated to react to actual demand. Accumulation of all operational errors resulted in too much water at the tail-end. The current operation was simulated using SIC model. The overall performance of all the offtakes given in Table 2 indicates that continuous operation at 80% of the design discharge, yields Delivery Performance of Ratio (DPR) 72% and Operational Performance (Eop ) of 74%. The Eop is less than unity because the volume of water supplied was more than the effective volume. About 26% of water was lost due to excessive supply. 7.2 Proposed Operational Strategies After modernization of USC irrigation system, the intension was to operate the system more in demand responsive mode, so that the pattern of water deliveries matched with the actual crop water requirements. It was observed that even after IMT, there was no significant evidence of operation of head regulator of the distributary due to increased water deliveries. The traditional mode of running the distributary at or near the full supply level and only making significant reduction during heavy rainfall has continued more or less unchanged. The existing operating pattern suggests that there is considerable potential for development of effective responsive management of the distributary. Chowki Distributary has been handed over to the farmers’ organization (FO) and it is managed by the FO according to IMT terms and conditions. The operational plan for head regulator of the distributary was developed for the FO. The FO assesses the cropping pattern and cropping intensity with the help of Water Users Association at tertiary level to estimate the crop water requirements. The accumulated net irrigation requirements of all the offtakes of the distributary is communicated to the Water Dispatch Officer (WDO) of Regulation Cell, Swabi for onward submission to the Swat Canal Area Water Board (SCAWB) for receiving water share from Frontier Irrigation and Drainage Authority (FIDA). Releases are governed by the indents and share of the distributary.
Table 2 DRP and Eop at different design discharge
Operation
VD (m3 )
VS (m3 )
VEFF (m3 )
DPR
Eop
80%Qd (80–90) %Qd (75–90) %Qd
231,552.00 231,552.00 231,552.00
181,999.00 185,473.15 178,989.70
121,657.42 182,134.64 140,327.92
0.72 0.80 0.77
0.74 0.98 0.78
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2.00
Performance Indicators
DPR
Eop
1.50
1.00
0.50
0.00 260
309
819
987
1867 2063
Head
2795 2970 4289
5510 5930 6185
Middle
6890
Tail
Position of the Offtake from the Distributary Head Regulator-(m) Fig. 5 Operational performance under fix frequency (80–90%Qd )
Fixed frequency operations at distributary head regulator have been analyzed using SIC model. It is proposed that first operation of the distributary head regulator should be between 7 and 8 a.m. and the second operation should be between 3 and 4 p.m. The discharge at intake should be increased in the morning and it should be reduced at night, keeping in view the fact that existing irrigation deliveries have no match with the crop demand. The reduced flow in the afternoon will ultimately control the wastage of irrigation water at night. As the system is downstream controlled below the distributary head regulator, thus there is no need to exchange operational information with other gate operators except the President of Farmers Organization (FO) and Area Water Board (AWB) office.
Performance Indicators
2.00
DPR
Eop
1.50
1.00
0.50
0.00 260
309
819
Head
987
1867 2063
2795
2970 4289
Middle
5510 5930
6185 6890
Tail
Position of the Offtake from the Distributary Head Regulator - (m) Fig. 6 Operational performance under fix frequency (75–90%Qd )
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7.3 Proposed Scenarios The first operation is proposed for the second decade of May to third decade of July. The operation of the distributary head regulator is based on 80–90% of design discharge i.e. to run the distributary for 9 h i.e. (from 7 a.m. to 4 p.m.) at 90% of the design discharge (2.76 m3 s−1 ) and for 15 h (from 5 p.m. to 7 a.m.) at 80% of the design discharge (2.50 m3 s−1 ). The overall DPR is 80% indicating optimal water delivery and Eop is 98% which indicates that no water is spilled as the volume supplied is approximately equal to the volume effectively used (Table 2). The effect of distributary head regulator on the individual offtake along the distributary is shown in Fig. 5. Two offtakes at 1,867 and 2,063 m are drawing 150% and 140% of the design discharge. The second operation at 75–90% of the design discharge is proposed from first decade of August till end of April. The operation of the distributary head regulator is based on 75–90% of the design discharge i.e. to run the distributary for 9 h i.e. (from 7 a.m. to 4 p.m.) at 90% of the design discharge (2.76 m3 s−1 ) and for 15 h (from 5 p.m. to 7 a.m.) at 80% of the design discharge (2.30 m3 s−1 ). The overall DPR and Eop of all the offtakes are 0.77 and 0.78 respectively. Therefore, performance at 75–90% of the design discharge is in the acceptable range. This is potentially viable compromise because the crop demand during the said period is less as compared to the existing water deliveries. The behaviour of individual offtakes shown in Fig. 6 indicates that DPR and Eop of the head and tail offtakes are in the acceptable range.
8 Conclusions Simulation of the irrigation system operation in advance is quite valuable to select the optimal operation alternative. The operational performance scenarios simulated using SIC model have been found to be useful for better understanding the hydraulic behaviour of the canal under unsteady state condition. Simulations by the model suggest that fixed frequency operations at 80–90% of the design discharge from May to July, and 75–90% of the design discharge from August to April will improve operation of the canal. These scenarios would reduce the wastage of water at night.
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