A study of water distribution from a branch to distributary canals: A case study of Gugera Branch,Punjab, Pakistan

This study was conducted on Gugera Branch of Lower Chenab Canal, Punjab, Pakistan. Sample distributaries off taking from Gugera Branch were selected for the study. The existing conditions of water distribution among the distributaries were studied. Field data were collected during the whole of 1988. Field observations suggested that the variability at the head of distributaries is much greater than the variability in the Gugera Branch under existing operational practices. The distribution of water among the distributaries is rarely in accordance with design criteria. Some channels get priority over other channels. The annual closure period varied from 17 to 41 days for different channels. The discharge at the head of distributaries remained lower than the standard operational range for 69 to 183 days in a year. The data suggested that a regulating gate at the head of the distributary can reduce discharge variation up to 2.4 times compared with a Karrees System (wooden stop logs used for water regulation). The data indicated that the adjustments in the head gate of a distributary on daily basis can substantially improve discharge conditions at the head of distributary. Rotational schedules are not being followed as per design and need to be improved. Most of the existing head discharge relationships of discharge measuring structures are not reliable. A frequent calibration of these structures is recommended.     

Application of a hydraulic model for testing management decisions at distributary level

Summary This study was conducted on the Lagar Distributary of Gugera Branch of Lower Chenab Canal, Punjab, Pakistan. A computer model MISTRAL was adopted for evaluating management options. The study showed that the model can be used as a decision support tool for prioritizing management options. The model suggests that under current physical conditions of this distributary the combination of rotation between the distributaries and along the distributary canals can improve the equity of water discharge. For example, in case of Lagar Distributary the discharge of tail outlets can be increased threefold by introducing rotation between the tail of the distributary and an offtaking minor canal. A small decrease in the discharge of the minor would result from adopting this option. A combination of rotations between this and neighboring distributaries and along the Lagar itself can increase the discharge of tail outlets up to seven times. The results of the model indicate that operational changes can improve the discharge of tail outlets to some extent, but the improvement of physical conditions of the distributary is needed to achieve equity conditions, as specified in the design.     

Productivity of Rice—Wheat Cropping System in a Part of Indo-Gengetic Plain: A Spatial Analysis

Investigations were made to study the effect of unequal distribution of canal water in land and water productivity of the rice—wheat cropping system in terms of head—tail relationship in Bhakra Canal command, Haryana. Information on water supply, agronomic practices, crop yield, etc.,were collected from 216 farmers comprising 36 farmers each from the head, middle, and tail watercourses of two minors during year 2000–01. The unequal supply of canal water and presence of marginal quality groundwater creates large variations in the cropping pattern, irrigation application, and land and water productivity of the irrigation system. The groundwater of tail reaches, being saline in nature, was about 25% less productive as compared to head reaches. The unavailability of canal water in the tail reaches creates more dependency on groundwater. Due to its poor quality the crop production in the tail reaches was less by 10 to 20% in case of wheat, and 20 to 40% in case of rice, as compared to head reaches. Groundwater transfer from head to tail reaches and cultivation of low water requiring salt tolerant crops/varieties would be helpful in reducing the productivity gap and increasing the profitability of the farms in the region.     

Using a hydraulic model to prioritize secondary canal maintenance inputs: results from Punjab,Pakistan

A computer-based hydraulic model,RAJBAH, was used to assess the utility of such models to assist and support canal system managers in planning and targeting maintenance activities on secondary canals. The work was conducted on Lagar distributary, a secondary channel off-taking from Upper Gugera Branch canal, Lower Chenab Canal system, Punjab, Pakistan. Measured discharges of off-takes and water levels along the distributary for premaintenance and post-maintenance periods were obtained. These data were used to assess the impact of actual maintenance inputs at specific locations identified in a model application in 1989. The predicted results of the model were satisfactorily close to conditions measured in the field. The study confirmed that suitably calibrated hydraulic simulation models can be effectively used in a decision support planning capacity to target and prioritize maintenance inputs for secondary canals in the irrigation systems of Pakistan's Punjab.     

Flexibility analysis of irrigation outlet structures using simulation of irrigation canal hydrodynamic model

The Upper Swat Canal (USC) System became operational in 1917–1918 in North West Frontier Province (NWFP) of Pakistan. The rehabilitation and modernization of the USC was undertaken with a view to overcoming the shortage of water supplies for irrigation. The water allowance was enhanced from 0.39 to 0.77 Ls⁻¹ ha⁻¹ in the study area. Recently, the operation and management of a secondary canal or ‘distributary’ was transferred to the Farmers Organization (FO). This distributary named ‘Chowki’ offtakes from the Maira Branch of the USC. The cultivable command area (CCA) of this distributary is 4,306 ha and it serves 1,485 beneficiaries. A management committee on Chowki Distributary was formed in 2003. This distributary consists of one main and two minor channels having twenty-eight direct outlets. The Simulation of Irrigation Canal (SIC) hydrodynamic model was used to evaluate the flexibility of Chowki Distributary. The model was calibrated at 100, 80 and 70% of the design discharge (Q _d) and it was validated at 90, 85 and 60% of the design discharge. The observed and simulated water levels were in close agreement with each other for the calibration and validation periods. The statistical analysis and paired t-test indicate that the model results are not statistically different from the measured values at 1% significance level. The simulated results of the SIC model were applied to studying flexibility of the outlet structures along the Chowki Distributary. The flexibility analysis demonstrates that poor performance is inbuilt into the system due to inadequate control over the accuracy of the crest setting during the construction of the outlets.     

Water distribution on a large distributary,Tungabhadra, India

Results are presented of field research on water distribution in the command area, covering 18,200 ha, of a secondary irrigation canal in the Tungabhadra Left Bank Scheme, Karnataka State, India.The official objective of the Scheme and the resulting implications for the water distribution are discussed first. An explanation of the planning and operation of the water distribution follows.The results are based on analyses of the water flows taken from the D36 secondary canal and distributed along the canal to the pipe outlets (inlet structures to the tertiary units), and of the canal section rotation practised along the canal. The analyses concentrate on three dimensions of the water supply:The design flows, according to the official Scheme objectives and criteria;The targets, as set by the system operators before every season;The actual distribution procedures and flows, as observed during the operation.The analyses, supported by flow measurement data, illustrate that the water distribution is not based on consistent and clear criteria and procedures, but that it is the outcome of varying compromises, decided upon pragmatically by the field staff, to bridge the gap between the farmers' demands and the upstream constraints to water availability. This paper explains the widespread phenomenon of head reaches taking too much water, leaving little or nothing for the tail end of the canal.     

Conjunctive use of canal and groundwater in Punjab,Pakistan: management and policy options

Data from 41 watercourses commands in Pakistan show that, as expected, farmers in head end reaches of canals receive more canal water than those in tail end reaches. Contrary to conventional wisdom, however, these head end farmers also use more groundwater than those at the tail end. Overall, groundwater plays a more important role in irrigation than surface water, ranging from 65% dependence on pumped water in head end areas to over 90% in tail end areas. This means that groundwater is no longer supplemental to canal water, but is an integral part of the irrigated agricultural environment. However, the cropping choices of farmers appear to reflect the amount of good quality canal water they receive: head end farmers are able to grow more high value basmati rice in the summer and more vegetables in the winter, leaving tail enders to rely on less valuable crops such as fodder and wheat.Tail end areas are not only deprived of their fair share of surface water: they have to pump proportionately more groundwater which shows decreasing quality towards the tail. Typically, head end areas have groundwater with EC values of less than 1.0 dS/m, rising to over 2.0 dS/m in tail end areas. When the quality of both surface and groundwater used by farmers is examined, only the top 40% of the distributary gets water of adequate quality, the next 40% get below average quality, while the tail 20% of farmers irrigate with water that is classified as saline.Because of higher dependence on more expensive groundwater tail enders use less water per unit area, thereby reducing the leaching requirement. The result is a clear increase in soil salinity from head to tail along distributary canals, and there is some evidence of land abandonment in tail end watercourses due to excess salinity.The implications of these results are far reaching. Government policy includes plans to divert significant quantities of fresh canal water to areas underlain by saline groundwater on the basis that farmers already have adapted to pumping fresh groundwater. The results reported suggest that if this policy were implemented, there is a risk that over-dependence on fresh groundwater could lead to an intensification of the rate of soil salinization and deterioration of quality in areas currently classified as fresh groundwater zones.At present, the location and utilization of privately owned shallow tubewells is not monitored, and thus it is not possible for government agencies to determine just how much water of different qualities is being used. Further, canal water deliveries, public deep well monitoring, watercourse monitoring programs, soil salinity measurements, and agricultural performance monitoring are all scattered among different agencies and organizations, making the task of effective conjunctive management of surface and groundwater even more difficult.Conventional wisdom: Groundwater in Pakistan ... where it exists within the canal system ... is used to supplement surface water supplies to meet peaks in demand. (WAPDA, 1990)     

Changes in hydraulic performance and comparative costs of lining and desilting of secondary canals in Punjab,Pakistan

Observations on the hydraulic changes of lining of secondary canals in Punjab, Pakistan show that performance improvement objectives are not always achieved. If lining is justified on the basis of water savings through reduced seepage losses, then tail end areas should receive improved water deliveries. Observations in two distributary canals following lining do not demonstrate significant improvements in tail end conditions. Justification of lining on the basis of more stable water conditions is also hard to identify; reduction in the variability of discharges 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 the 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.     

Improved 0–1 programming model for optimal flow scheduling in irrigation canals

An improved 0–1 programming model was presented for optimal flow regulation and optimal grouping and sequencing of outlets in irrigation distributaries, under restrictions of both the rotational period and the incoming flow rate into distributaries. The problem was solved using a commercially available 0–1 programming software package. The example computations indicated that this model could effectively provide a constant flow rate into the canal during most of the rotation period, and thus reduce the frequency of headgate operation. This formulation also minimized the accidental water wastage by appropriately sizing the canal cross-section.     

渠道水利用系数计算方法及误差分析

以内蒙古河套灌区隆胜示范区为研究实例,选取隆胜示范区永刚分干和西济支渠衬砌段测流成果,采用两种近似方法计算渠道水利用系数,即采用渠道首端流量、单公里长度渗漏损失流量和渠道总长度3个参数估算渠道水利用系数,并分别与准确计算渠道水利用系数的方法首尾法即采用同时测流的渠道上下断面流量的计算方法比较,进行误差分析,提出了在缺乏资料前提下相对准确的近似计算渠道水利用系数的方法,用于灌区节水改造后渠道水利用系数的估算和预测,对于计算灌区节水潜力和评判灌区水利用效率都有着十分重要的意义.     

Performance evaluation of an irrigation command area using remote sensing: a case study of Mahi command,Gujarat, India

Multi-temporal remote sensing (RS) data-based crop inventory, generation of vegetation spectral index profiles and crop evapotranspiration estimation were carried out over the Mahi Right Bank Canal (MHRC) command (212,000 ha) in Gujarat, India, using Indian Remote Sensing Satellite (IRS)-1C Linear Imaging and Self Scanning-III (LISS-III) and Wide Field Sensor (WiFS) data. Distributary-wise, three RS-based performance indices, namely, adequacy (AI), equity (EI) and water use efficiency(WUE) were computed. AI was computed by comparing the crop water requirement with the water release data. EI was evaluated by observing the head-to-tail difference in two distributaries. It was found that water availabilty was in excess along main canals and branch canals. In cropped area, it was less and crop condition was poor towards the tail ends of the command area. WUE was computed as the ratio between the area under the vegetation index profile and the water applied. The three RS-based indices could rank the performance of the distributaries and also identify those having problems in water allocation and utilization.     

Study of feasibility of night-closure of irrigation canals for water saving

The feasibility of closing distributary canals at night was investigated in a recently modernized surface irrigation system in Pakistan, the Upper Swat-Pehur High Level Canal system. Increased water supply, greater delivery capacity and the introduction of downstream control potentially allow more flexible service. In the command area of Maira branch of this system, farmers are anyway abandoning night-time irrigation, as they can meet their needs from improved supply during the day. They practice night irrigation only during the times of peak crop water demand. The rotational delivery system, known as warabandi in the sub-continent and Dauran in Arabian countries, has even broken down in the day in some parts of the command area. This is believed to be typical of systems with more than adequate water supply.A simulation study was undertaken using the CanalMan software developed by Biological & Irrigation Department, Utah State University, Utah Logan, USA. Primary data collected in one distributary canal and the two minors connected to it was utilized for simulations. The feasibility of night-time closure depends on the speed of filling and emptying the canal each day, and the time required to meet full irrigation demand during the day. The results show that where canal lengths are less than 5 km, in this system, there is good potential to make savings, which can be realized at system level through reduced demand on supplemental supplies from Tarbela Dam.     

Application of unsteady flow hydraulic-model to a large and complex irrigation system

Canal hydraulic-models can be used to understand the hydraulic behavior of large and complex network, to evaluate their performance and to improve the operation and management of such systems at low cost. In this study, the canal hydraulic-model (CANALMAN) was applied to the right bank main canal (RBMC) of the Kangsabati irrigation project, West Bengal, India. The canal is 33.17 km in length and has eight distributaries. The model was calibrated for the irrigation period of 19 July–1 August 1997 and validated for 18–28 October 1997 and 23 July–5 August 1996. The observed and simulated inflow-rates were in close agreement with each other for both the calibration and validation periods. The calibration parameters, Manning’s roughness-coefficient and seepage-loss rate, were found to be 0.016 and 160 mm per day, respectively. The means of observed and simulated inflow-rates were not statistically different at 1% level of significance for both the calibration and validation periods. The calibrated model was subsequently used to study the adequacy of water supply during Kharif (rainy) season for the year 1996. Comparison between simulated (required) and observed (supplied) inflow-rates revealed that the supply of irrigation water was in excess most of the time. The average water supply during the entire Kharif season was about 13% higher than the model-simulated required flow-rate, which establishes the fact of over-irrigation in the head reach of the main canal system. The simulation results suggest that the CANALMAN-model can be successfully used for the operation and management of the RBMC of the Kangsabati irrigation project.     

Effects of construction defects on hydraulic performance of Kalpani distributary, NWFP, Pakistan

The hydraulic performance of canals designed to deliver water by proportional allocation is highly dependent on the accuracy of construction of water division structures. If construction is inaccurate then inequity of water delivery is built into the system from the onset. A survey of hydraulic performance of Kalpnai distributary in NWFP Pakistan immediately after construction showed that the canal could only deliver 90% of designed discharge due to deficiencies in construction of two siphons, and that the tail end of the canal only received 70% of designed discharge. When operated at 70% of design discharge tail end reaches received 50% of designed discharge. Measurements of outlet structures showed that 57% of structures were built as intended and had not been damaged. All orifice outlets delivered more than 115% of design discharge and on average delivered 40% more than intended. Only 20% of open flumes were within 10% of design width, while 58% were more than 30% wider. As a result of these construction defects many watercourses were able to obtain much higher discharges than intended. The lack of control gates means there is no managerial remedy to redress the existing inequity. The only solution is to reconstruct a high proportion of outlet structures. Potential causes of poor construction are many, including lack of involvement of the agency responsible for subsequent operation, lack of dialogue with water users, and lack of accountability built into the project framework.     

A model for equitable distribution of canal water

The equitable distribution of canal water is imperative to ensure social justice as well as crop productivity. In north-west India and Pakistan, water from the tertiary canal (watercourse) is distributed to the farmers through a rotational system of irrigation. In this system the duration of supply to each farmer is in proportion to his holding in the outlet (watercourse) command, without considering the seepage loss. The rate of seepage loss increases with increase in length of watercourse from head to tail. Thus, the farmers in the lower reaches get much less water per unit area than the farmers in the upper reaches. The farmers must be compensated for the seepage loss. Therefore, a model was developed to ensure equitable distribution of water to the farmers located on a watercourse in proportion to their land holdings giving due compensation for the seepage loss. The model is based on the assumption that soil throughout the length of flow is homogeneous and loss through evaporation is negligible. The model developed ensures an equitable distribution of water to the farmers according to their land holdings. A comparison of existing and revised time allocation reveals that the farmers located in the upper reaches were getting more time (up to 12.2 min per unit area), while the farmers located in the lower reaches have been getting less time (up to 28.1 min per unit area). The existing allocation of time of 0.75 h per unit area to all the farmers according to the old rules was revised to 0.546–1.219 h per unit area from head to tail. The conclusions drawn suggest that the strategy developed here should be adopted elsewhere in the existing system of irrigation for equitable distribution of canal water. Received: 21 December 1999     

Water Delivery Performance in the Doroodzan Irrigation Scheme, Iran

Delivery performance ratio was used to assess thewater delivery performance in an irrigation district in theDoroodzan Irrigation System in Iran. The measurements wereapplied to three selected irrigation canals and their tertiaryoutlets during five consecutive irrigation cycles. The canalswere located at the head, middle and tail end of the irrigationdistrict.Performance indicators reveal that the physical system and themanagement could respond to the delivery of the intended supply.The indicators show a better reliability performance than theequity performance in water delivery at the tertiary outlets. Theresults from the Doroodzan Irrigation System reveal that thesystem could not deliver water according to the real crop waterrequirements. The actual overall efficiency was used to quantifythe water delivery performance in terms of deficit and excesswater. The equity and reliability performance was illustrated byusing the spatial and temporal variation of the expected overallefficiency at the district level.     

Strategies to improve manual operation of irrigation systems in Sri Lanka

Improvements to normal operational procedures are investigated for the main types of irrigation system identified in Sri Lanka. Scheduled and unscheduled changes of flow regime the systems are likely to experience and the opportunities for improved operations related to the physical characteristics of each type are analyzed.Performance of several alternative manual operational procedures are evaluated and compared using a hydraulic model (Simulation of Irrigation Canal, SIC) for three different irrigation subsystem types (Single Bank canal; Double Bank canal; Canals with intermediate Storage). Results of these simulations show that current practice, based on a fixed frequency of operation of 12 hrs and a target water depth set to the spill level of the cross-regulator, is not far from the optimal for systems without on-line storage. A slight improvement can be expected if the frequency of operation is increased to 6 hrs. For systems with on-line storage it is recommended to split operational procedures into two parts, one related to the canal and one to the storage. Among different options investigated, discharge control at the downstream regulator of the storage appears to be the most reliable as it performs well whatever operation procedures are selected for the canal.Irrigation systems in Sri Lanka are subject to frequent positive flow changes (Supply fluctuations, Runoff, Return-flow changes). As far as water management is concerned, improvements to be expected from normal operation procedures appear to be somewhat limited because management of flow changes is not an objective. For instance little effort is made to harvest runoff under the current practices. One conclusion of the study is that new strategies for the harvest, storage and release of positive flow changes should be tested and, where appropriate, implemented to improve the overall efficiency of operation in irrigation systems in Sri Lanka.     

On-farm water management in saline groundwater area under scarce canal water supply condition in the Northwest India

The study investigates the possibility of enhancing crop water productivity in the parts of Northwest India where groundwater quality is marginal and canal water supply is severely scarce. Soil, Water, Atmosphere and Plant (SWAP) model was calibrated and validated in three farmers’ fields with varying canal water availability and groundwater quality in the Kaithal Irrigation Circle of the Bhakra Canal system, Haryana. On the basis of predicted and observed soil water content, pressure heads, salt concentration at 2 week intervals and crop yields, the model was found suitable for use in the region. A few nomographs were prepared to provide a graphical method to predict the effect of different combinations of water quality and depth of water application on crop yield and soil salinity and to help develop some guidelines to the farming community. Water management alternatives at the field level were suggested to increase the yield and to maintain soil salinity below threshold level. The application of frequent irrigation in precisely leveled field would help in achieving 10% higher yield even when saline groundwater of 11 dS/m is used for irrigation.     

Performance assessment of Doroodzan irrigation network by steady state hydraulic modeling

There is a need for improvement in the operation and management of many irrigation and drainage systems worldwide. Computer models are used widely for better management. One of such models is HEC-RAS that was applied to Ordibehesht Canal at the Doroodzan irrigation network, northwest of Fars province in the southern Iran. The model was calibrated and validated for two irrigation seasons during 2001 and 2002. The present gate opening rules used to control the offtakes were simulated by the model and the discharge reductions were evaluated. Discharge reduction of offtakes due to discharge reductions at system source were evaluated by the model. Results show that the present rule is not appropriate for the present system. Fluctuations of discharge at the beginning of canal show considerable and nonuniform changes in discharge of offtakes along the Ordibehesht Canal. The head offtakes show more reductions in the water delivered than middle and tail offtakes. A new sensitivity indicator was defined and used to show the response of offtakes due to discharge changes at system source. The study also shows that HEC-RAS model can be used successfully for a large and complex irrigation system for evaluation of its performance in the absence of observed flow data and improvement of irrigation management plans.     

Adjusted friction correction factors for center-pivots with an end-gun

A new method for calculating total friction head loss in center-pivots with an operational end-gun was developed. The proposed methodology is based on adjusting the previous friction correction factors for center-pivots with end-guns in order to correct their paradoxes and shortcomings. Equations presented in the current work are developed for center-pivots with a finite number of outlets along the lateral and constant outlet spacing and discharge as well as constant discharge and variable spacing. The proposed formulas depend on the number of outlets along the supply pipeline, the exponent of velocity term in the friction formula used and the distance that water is jetted by the end-gun. All equations reduce to the well-established equations for the friction correction factor when the end-gun is turned off. The equations presented here compare well to the stepwise friction calculation method, yet correct slight errors in the way that these friction correction factors were calculated in the past.