Research Report

International Water Management Institute

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ISSN 1026-0862

35

Modernizing IrrigationOperations: Spatially DifferentiatedResource Allocations

D. Renault and I.W. Makin

ISBN 92-9090-386-4

Research Reports

IWMI’s mission is to contribute to food security and poverty eradication by fosteringsustainable increases in the productivity of water through better management of irriga-tion and other water uses in river basins. In serving this mission, IWMI concentrateson the integration of policies, technologies and management systems to achieve work-able solutions to real problems—practical, relevant results in the field of irrigation andwater resources.

The publications in this series cover a wide range of subjects—from computer mod-eling to experience with water users associations—and vary in content from directlyapplicable research to more basic studies, on which applied work ultimately depends.Some research reports are narrowly focused, analytical, and detailed empirical studies;others are wide-ranging and synthetic overviews of generic problems.

Although most of the reports are published by IWMI staff and their collaborators,we welcome contributions from others. Each report is reviewed internally by IWMI’s ownstaff and Fellows, and by external reviewers. The reports are published and distributedboth in hard copy and electronically (http://www.cgiar.org/iwmi) and where possible alldata and analyses will be available as separate downloadable files. Reports may becopied freely and cited with due acknowledgment.

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Research Report 35

Modernizing Irrigation Operations:Spatially Differentiated Resource Allocations

D. Renault and I.W. Makin

International Water Management InstituteP O Box 2075, Colombo, Sri Lanka

ii

The authors: D. Renault is Irrigation Specialist and I.W. Makin is Head of Design andOperation Program both of the International Water Management Institute (IWMI).

This report draws on observations during a collaborative study between the IrrigationDepartment of Sri Lanka (SLID) and IWMI, which received financial support from France.The authors gratefully acknowledge the critical comments and suggestions received fromcolleagues in IWMI and SLID that have helped shape the ideas presented here.

D. Renault, and I.W. Makin. 1999. Modernizing irrigation operations: Spatiallydifferentiated resource allocations. Research Report 35. Colombo, Sri Lanka: InternationalWater Management Institute.

/ modernization / irrigation systems / operating policies / water use / irrigation canals /sensitivity analysis / case studies / models / resource allocation / Sri Lanka / KirindiOya /

ISBN 92-9090-386-4ISSN 1026-0862

© IWMI, 1999. All rights reserved.

Responsibility for the contents of this publication rests with the authors.

The International Irrigation Management Institute, one of sixteen centers supported bythe Consultative Group on International Agricultural Research (CGIAR), was incorporatedby an Act of Parliament in Sri Lanka. The Act is currently under amendment to readas International Water Management Institute (IWMI).

iiiiii

Contents

Summary v

Introduction 1

Background on Canal Operation 2

Opportunities and Constraints in Water Service 5

Case Study of Kirindi Oya Irrigation Settlement Project, Sri Lanka 12

Conclusion 19

Literature Cited 19

v

Summary

Modernization of irrigation implies interventions indifferent components of system management. Thisreport focuses on operations and proposes amethodology for improved assessment of irrigationcanal behavior and the environment in whichoperations take place. An underlying assumption isthat irrigation systems are generally heterogeneousand, therefore, the allocation of operationalresources should be matched to the spatialdistribution of management requirements.

A descriptive model of irrigation systems ispresented based on consideration of threedomains. First, the cause, frequency ofoccurrence, and magnitude of perturbations to theflow regime are considered as the perturbation

domain. Second, the behavior of the physicalsystem when subjected to perturbations isconsidered the sensitivity domain. Last, the impactof system operations on agricultural yields isexamined in the vulnerability domain, which enablesthe specifications for a required “water service.”

Combining the vulnerability and sensitivitydomains enables the definition of the precision withwhich systems must be operated. The inclusion ofthe perturbation domain allows specification of themode of operation required to achieve the desiredwater service, including specification of therequired frequency of intervention. All of thisenables the demand for operating at a spatiallydisaggregated level to be defined.

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Modernizing Irrigation Operations: SpatiallyDifferentiated Resource Allocations

D. Renault and I.W. Makin

Irrigation modernization is increasingly recognizedas a fundamental transformation in themanagement of water resources within agriculturalareas. Such transformation may includeimprovements to physical and/or institutionalstructures, rules and water rights, water deliveryservices, accountability mechanisms, andincentives. This report discusses howmodernization provides an opportunity to redefineand update operational procedures within irrigationschemes. By incorporating broader perspectivesand taking more consideration of the spatialdistribution of significant variables, this reportdefines new approaches for the allocation ofoperational resources.

The objective of this report is to present animproved methodology for evaluating the resourcedemands for effective canal operations to enablemore cost-effective operational management. Thefundamental basis of the proposed approach iswhether or not operational requirements arehomogeneously distributed throughout a givenscheme. If not, operations require differentialresponses in different sections of the scheme.

Determining the demand for operationalresources consists primarily of answering thefollowing questions:

• What service to the users?

• What mode of operation?

• At what precision?

• With what frequency of checking andintervention?

Introduction

• What monitoring system is required?

The need to reevaluate and updateapproaches to operations is given impetus by thetremendous changes that have occurred in theirrigation sector over the last few decades. Theseare the consequences of increasing competitionfor water and financial resources, as well as ofgrowing concerns about the environmental andhealth impacts of irrigation. Water management isno longer narrowly focused, but must embrace abroader perspective including water quality,conjunctive management, multiple uses of water, awatershed perspective, new water rights, andpriorities for distribution. A traditional quantitativeand rather uniform management system onirrigation schemes is no longer sufficient toaddress current issues. Further, these trends willcontinue and system operators will have todevelop more cost-effective operational plans tosatisfy the increasingly influential user-payers. Theservice of irrigation will be—more than in thepast—the result of negotiations between theservice provider and the service user and a trade-off between costs and benefits.

As opportunities to develop new areas forirrigation are increasingly restricted, many existingirrigation schemes are, or in the near future willbe, undergoing major changes, either physical orinstitutional or both. There is a crucial need toscrutinize the basic irrigation activities, operation,and maintenance, to ensure that systems becomeeconomically sustainable.

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Canal Operation in Technical Literature

Canal operation and flow control techniques arewell documented, particularly for system designanalysis, e.g., by Zimbelman (1987), Paudyal andLoof (1988), Plusquellec (1988), Plusquellec, Burt,and Wolter (1994), and RIC (1997). However, thereare few published studies addressing howmanagers should operate existing systems,evaluate the operational requirements, or allocateresources; or describing the efforts required tooptimize system performance. In many schemes,a mixture of rule-of-thumb and local experience isthe basis for operational decision making. There isno standardized base for retention of operationalexperience while, due to staff rotation, there is arisk of permanent loss of knowledge if suchinformation is not formally recorded in anunderstandable form.

Any new approach to canal operations mustbridge the gap between actual on-sitemanagement and the official Plan for Operationand Maintenance (POM), and other suchoperational guides. These guide manuals areincreasingly required by authorities and fundingagencies at the completion of structural works(new projects or rehabilitation). However, the factthat the operational framework cannot be fullyplanned at the design stage must be recognized,so that fine-tuning over some years of practice isa fundamental requirement (Uittenbogaard andKuiper 1993). Thus, it is proposed that anadaptive or learning process is more preferable tostrictly prescriptive approaches (LBII and WPCS1990; Skogerboe and Merkley 1996).

Operation in the Irrigation Process

The word operations refers to both themanipulations of physical structures in theirrigation system to implement management

decisions about water allocation and schedules ofdelivery and distribution. Operations are also theroutine actions to minimize the impacts ofperturbations by maintaining steady or quasi-steady-state water profiles in the system, inaddition to preventing overtopping at peakdischarges.

Operations are routinely required to implementdistribution decisions and, as a consequence, theterms are sometimes confused even though theyare fundamentally different. To clarify the thinking,technical irrigation management implies threelevels of decisions: allocation, scheduling, anddistribution, and one level of implementation:operations.

Operation and Type of IrrigationSystems

Operational requirements of irrigation systems arenot identical. Some are highly automated and,although requiring larger investments inconstruction, often require fewer resources (humanand financial) for day-to-day operation. Othersystems are manually controlled and require fulland intensive operations during irrigation. Irrigationsystems may be classified as:

• Fully operated systems where all structures(intake, outlets, cross-regulators) requireregular and routine operation during irrigation(setting on/off, setting, and monitoring).

• Nonoperated systems that generally operateon the proportional distribution principle, andare common in India and Pakistan. Fixeddividing structures ensure an equitabledistribution of water. No operations arerequired to adjust ongoing flows within the“structured system” (Shanan 1992).

Background on Canal Operation

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• Minimal operation systems, such as thoseequipped with modules and combined withautomatic or fixed regulators. Interventions aregenerally limited to on/off operations and flowregulation is achieved by control modules orbaffles.

This classification of control systems isessentially valid only for intermediate level canals,such as distributaries. Main canal systems andfield canals are generally fully regulated.Therefore, a logical conclusion would be thatwhatever control technique is used in theintermediate distribution system, major irrigationsystems include (at least partly) portions withgates that must be operated.

The Basic Assumption ofHeterogeneity and the Spatial Analysis

In general, technical manuals for irrigationoperations, implicitly assume homogeneity: first,homogeneity in the requirements for operation and,therefore, homogeneity in the distribution ofoperational efforts. In many cases, thisassumption simply does not hold true. Rather, thebasic assumption in operating an irrigation systemshould be that the scheme is heterogeneous,unless it can be clearly shown to behomogeneous.

There is limited literature on heterogeneity inirrigation systems. Poh-Kok (1987) presented anoteworthy approach for design of an irrigationsystem proposing the concept of irrigation formand its context. Poh-Kok proposed that both formand context must match in order to achievesuccess. He considered the assumption of“heterogeneity” a generic term regroupingvariability, uncertainty, diversity, and complexitybefore presenting a conceptual model of irrigationas a consistent aggregation of elementaryhomogeneous units. These elementary units weredefined as a Socio-Geographic Unit (SGU),homogeneous in “form” and “context.”

Steiner and Walter (1993) considered thespatial variability of all factors influencing irrigationmanagement, such as the physical characteristicsof the context, the quality of infrastructure, etc.These authors later focused exclusively on spatialvariability of climate and simulated theconsequences of different allocation schedules.

Consideration of heterogeneity alsounderpinned the methodology developed bySchakel and Bastiaanssen (1997) for watermanagement at a large scale for the Bhakrasystem in Haryana, India. Irrigation managementthroughout an area of 1.2 million hectares wasdisaggregated into 67 homogeneousgeohydrological regions.

The authors fully support the assumption ofheterogeneity in system physical characteristics,in social and environmental contexts and,therefore, in the demands for operation. It isproposed that this assumption is valid not only forlarge-scale systems, but also for smaller ones, ofsay, one thousand hectares. Therefore,determination of demands for operationalresources should be based on spatial analysisleading to partitioning systems into elementaryunits with homogeneous characteristics, forconvenience called “subsystems.”

An important consideration is the link betweenheterogeneity and equity. It is clear that thejustification for the widespread application of thehomogeneity assumption was partly related to thegoal of achieving equity within a system. Thisgoal should not be ignored in any new approach tooperations. Without care, the introduction of theheterogeneity concept may conflict with equity; forexample, considering the value of a crop per unitarea could lead to reinforcing existing inequity byproviding better service to already well-servedusers.

The Methodology

Open-surface canals are subject to modification offlow characteristics (discharge-water depth)

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resulting from scheduled and unscheduled events.In the usual operational mode, the managementobjective is to maintain steady state conditionswhen such events occur. The methodologydeveloped here aims to characterize the frequencyand magnitude of perturbation events likely tooccur in a subsystem. The frequency of change inthe distribution pattern defines the perturbationdomain. By characterizing the physical propertiesof the irrigation structures and evaluating thebehavior of canal systems when operated oraffected by perturbations, the sensitivity domain isdefined. Finally, the analysis of the impacts ofoperation on agricultural yields, on theenvironment, and on the watershed enablesdefinition of the vulnerability domain.

Analysis of the vulnerability domain enablesthe definition of a global demand for “waterservices” for the multiples uses within the

scheme. This may be seen as a basis on whichspecific agreements defining the level of servicehave to be found between the service provider andthe users, particularly when the latter are bearingthe cost of the service. The concept of service inirrigation is receiving more and more attentionwithin the irrigation community (Huppert 1993;Hofwegen and Malano 1997) and is generallyperceived as much broader than water delivery. Inthis report though, the concept of water service isrestricted to water delivery, and is analyzedthrough classical performance indicators(adequacy-efficiency…).

Considering the required water serviceperformance, and then combining this with sensitivityanalysis of the infrastructure, enable the specificationof the precision of water depth control required (figure1). The mode of canal operation required is defined bythe combination of the vulnerability and perturbation

FIGURE 1.Overlay process for mapping distribution of efforts for canal operation.

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The Vulnerability Domain

Vulnerability is a generic term used here todescribe opportunities and constraints and/orimpacts of operation at different scales of spaceand time. Vulnerability of an irrigated area can beseen as the propensity to be positively ornegatively affected by irrigation operations. Forinstance, a highly vulnerable area would be a unitin which impacts and side effects of low-qualityoperation are high (sensitive crops, areas withoutdrainage facilities). Inversely, areas of lowvulnerability are those in which impacts andconsequences of low quality operation are eithertemporally or permanently dampened (rice fieldsare more tolerant to interruption of water supplythan other crops). “Vulnerability” extends beyondthe confines of water for crops and includesconsideration of larger-scale water managementimpacts.

Some of the wider aspects of watermanagement that define the vulnerability domaininclude:

Water quality. Modern agricultural methods andthe scarcity of freshwater result in irrigation havingto deal with water loaded with chemicals (pesti-cides, nutrients) and other pollutants.Acknowledgement of the importance of waterquality is one of the main challenges for currentirrigated agriculture, with implications for bothsurface water and groundwater. Many shallowaquifers are important for domestic supply. These

often receive some recharge from dry-seasonpercolation from irrigated areas representingsimultaneously a gift: an additional source, and athreat: pollution. In these situations, managers willhave to consider both uses and arrive at aneffective compromise.

Recycling of irrigation water. Drainage flowsfrom irrigated areas can be important assets inwater management. Losses in one place becomeinputs for other areas. The presence of suchrecycling can substantially ease the upstreammanagement problem by allowing less precision indistribution, knowing any surplus will not be lost.Return-flow systems represent an opportunity formanagers to store positive perturbations, forexample to harvest rainfall, as both drainage andsurplus irrigation are channeled back to theirrigation network itself.

Water harvesting and conjunctive management.Water harvesting during rainfall periods is animportant opportunity for water management.Specific operational procedures may be designedto maximize harvesting while preventing canalovertopping. Conjunctive use of water (surfacewater, groundwater, and rainfall) can provideadditional flexibility to farmers. Groundwater isfrequently used to compensate for rigidity or lowperformance in the surface water delivery system.Areas lacking access to additional supplies fromgroundwater should be considered for greatermanagement attention than areas where pumping

domains. Finally, the perturbation domain determinesthe required minimum frequency of systemobservation and regulation.

The approach can be viewed as a series ofoverlays of spatially distributed variables,

Opportunities and Constraints in Water Service

illustrated in figure 1. Although defined bytechnical considerations, the process must besociologically acceptable and also fit theobjectives of the irrigation scheme in terms ofagricultural development.

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facilities can compensate for inadequate and/orunreliable deliveries.

Soil and water salinity and waterlogging. Therise in soil and water salinity, and the increase inwaterlogged areas are environmental hazards ofgreat importance in arid regions. They represent asevere threat to irrigation schemes. It is clear thatoperation of irrigation systems must take intoconsideration the spatial distribution of thesehazards in order to provide a selective and locallyadapted water service. In practice, solutions arelargely site-specific and generic guidelines aredifficult to derive. But, as a principle, partitioningof the irrigated area should distinguish areaswhere freshwater has to be provided from areas inwhich excessive percolation should be avoided toprevent saline groundwater from rising.

Multiple uses of water. In many irrigationschemes, water is used not only for crops butalso for many other purposes including domesticwater supply, environmental uses, fisheries,perennial vegetation, and hydropower, amongstothers. Rules for multipurpose system operationsare complex because of potential conflicts insetting targets for the different uses and also, onoccasions, because of the lack of suitable ac-counting procedures. Multiple uses of water mayhave to be increasingly integrated in managementconcerns, whether or not these uses were consid-ered at the design time. A first step in the man-agement of multiple uses is to define a consistentset of water and productivity accounting proce-dures (e.g., Molden 1997).

Water rights, equity, and priorities in distribu-tion. Water distribution priorities may be based onlong-term rights and established uses. However, insystems experiencing water shortages, thesepriorities should define a policy to share limitedwater among shareholders. Priorities may bedefined based on the value of crops (high/low),soil- and water-holding capacity, etc. As themission of irrigated agriculture changes from

subsistence to more highly productive agriculture,it may sometimes be necessary to revise previouspolicies. There may be a necessity to avoiddamage to highly sensitive or high-value crops incase of water shortage. In many cases, distribu-tion policies should be reexamined and, whereappropriate, changed to enable new operationalobjectives.

Health impacts. Despite the positive effects ofirrigation on the rural economy and income offarmers there is no doubt that, in some circum-stances, it has also brought negative impacts onthe health of communities through vector-bornediseases. The maintenance of water in canals forlong periods of time can affect the reproductivecycle of disease vectors. The link betweensystem operations and community health can bestrong. The recommendations from health expertsare converging towards a requirement for morevariability in canal flow regimes to, for example,reduce the breeding of mosquitoes (Hunter et al.1993). However, there is a clear conflict betweenthese requirements for vector control and theirrigation management objective of stable waterprofiles. New techniques of operation may berequired where mosquito breeding is related toirrigation practices (Matsuno et al. 1999).

Location within the system. The impact ofoperations on the command area is evidentlygreater for structures located towards the head ofthe canal system. Therefore, location is includedin the analysis of vulnerability.

Finally, the study of each aspect of thevulnerability domain leads to a basis on which theprovider of service can further analyze therequirements for water service. The rationale hereis that a highly vulnerable command area requiresa high water service and vice versa. In modernmanagement, a further important step towards thedefinition of service is the negotiation with theusers of service (farmers, associations, cities,environmentalists, industrials, etc.) with the ideaof reaching an “agreed service” compatible with

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the hydrological constraints at scheme level andthe users’ willingness to pay.

Vulnerability, Water Service, andIrrigation Performance Indicators

The spatial characteristics of the vulnerabilitydomain can be converted into specific “waterservice” targets and measured with Water SupplyPerformance Indicators (WSPI) (Bos et al. 1994)such as adequacy, efficiency, dependability,timeliness, and equity, the common performanceindicators (Molden and Gates 1990). Flexibility ofaccess to water and reliability of deliveries areimportant criteria of performance that should alsobe considered (Renault and Vehmeyer 1999).

Performance indicators for operation can bederived from the vulnerability domain consideringboth water deliveries for irrigated crops and watermanagement in a broad perspective. In theanalysis presented here only the primaryindicators, adequacy, efficiency, and timeliness,are considered. Performance targets areexpressed as tolerances with respect to the targetdischarge rate as shown in equation 1.

(1)

Equation 1 shows that discharge at a givenlocation should be maintained within the twolimits, -z% or +y%, which constitute the tolerablerange for the target discharge.

The lower limit, z, is the tolerance factorrelated to adequacy, reflecting the capacity of thecommand area to accommodate water shortageand incorporates concerns about deliveries. Thisfactor, z, will vary as the period consideredchanges: a relatively high tolerance may bestipulated for a short period (days, weeks);however, the tolerance becomes smaller asthe period considered is extended (months,seasons).

The upper limit, y, is the tolerance factor forefficiency and reflects the capacity of asubsystem to accept surplus water (positiveperturbation). As for the z factor, the permissibletolerance y is a function of time and the physicalcharacteristics of the subsystem, such as theopportunities for return flows, reuse, etc.

A similar relationship can be developedconsidering the time of delivery, as described inequation 2.

(2)

where, u reflects the maximum acceptabledelay in water delivery; and v expresses themaximum allowable advance in delivery withoutwater loss.

The Perturbation Domain

Open channel irrigation systems are hydraulicallycomplex. In general, system operations arereduced to controlling water levels at cross-regulators in an attempt to maintain stable waterlevels and hence discharges at offtake structures.However, steady water level profiles seldom occurin irrigation systems due to both variations at theupstream boundaries of the system (perturbationsof intake flow rate) and the effects of operationalinterventions themselves. Hence, operation is anever-ending challenge as gate adjustments aremade to bring the system to the intended steadystate conditions; but under the influence ofperturbations, resulting from variable dischargesentering the system and the multiplicity of gateoperations, frequent adjustment are required.

A perturbation at a given location is defined asa change to the ongoing discharge. Such changesarise from two sources: first, planned changes inthe delivery; and second, unexpected or transientchanges. Unexpected or transient perturbationsare more difficult to manage precisely becausethey cannot be anticipated and therefore effective

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control depends on early detection (degree ofinformation).

Management of UnexpectedPerturbations

When a perturbation occurs in a canal, the effectstravel both upstream and downstream from thelocation where the perturbation was created.However, the main impacts are noticeddownstream. For analysis, the perturbation domainis divided, first, into generation and, second, intopropagation, which are also expressed as the“active” and “reactive” processes.

The active process can be analyzed in threeconstituent parts: (1) the causes of perturbations,such as return flows, illicit operation of structures,and drift in the setting of regulators; (2) thefrequency of occurrence; and (3) the magnitude ofperturbations experienced.

Causes, frequency of occurrence, and magni-tude of perturbations. Causes of perturbationsare to a large extent determined by the “network”properties of the system (source of supply,hydraulic layout, interconnections with othernetworks, such as drainage, unregulated return

flows, etc.). Renault and Godaliyadda (1999)describe these properties more fully. However, asecond source of perturbations is the operation ofthe irrigation regulation system itself. Offtake andregulator operations generate transient conditionsin the network, which may be translated upstreamto the parent canal from the dependant canal ifsubmerged flow occurs at the division from themain canal. In such cases, the sensitivity ofofftakes is the major determinant of the propaga-tion of the transient (Renault and Hemakumara1999). Perturbations may also be generated at theofftake due to deliberate or accidental modificationof the flow section, either due to changes in gatesettings (illicit operations) or by trapped debris(drift). Perturbations are also generated by un-scheduled operation of structures for unauthorizedwithdrawals, flow rejection, or overtapping. Table 1summarizes the major components and propertiescausing the generation of perturbations.

The position in the network controls thefrequency of occurrence of transients and partiallyexplains the notorious “head/tail” issue in irrigation.In this analysis, the occurrence and magnitude ofperturbations at any given point are dependent onthe numbers and the operational characteristics ofupstream structures (cross-regulators andofftakes). Generally, the more numerous and the

TABLE 1.Components and properties significant for unexpected generation of perturbations (adapted from Renault andGodaliyadda 1999).

Components Related properties Classes for partitioningfor operation

SourceSupply Fluctuations of source Reservoir River Canal branch Canal series

diversion diversion diversionDegree of control

Return flow (RF) Non-return flow (NRF)

Layout Variability of on-line Single bank canal (SBK) Double bank canal (DBK)Lateral flows discharge with runoff without runoff

Runoff ditches No ditches

Offtakes Upward sensitivity for Low Medium Highconveyance

Sensitivity to setting

Regulators Sensitivity to setting Low Medium High

User Illicit operation Discipline No discipline

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greater the sensitivity of upstream cross-regulators, the greater the magnitude andfrequency of perturbations. Inversely, for systemswith sensitive offtake structures, perturbationsgenerated in the head reaches will be attenuatedby upstream offtakes and the downstreamofftakes will experience smaller transients.

Perturbations are expected whenever achange in the distribution takes place andtherefore distribution policy (on-demand, supply-based, free-access) is a key determinant of thefrequency of occurrence of perturbations. Thegreater the flexibility of delivery service providedthe greater the frequency of changes indischarges in the canal system. Properconsideration of the impacts of service flexibilityis essential to identify the specific operationalmodes and structure characteristics required foracceptable performance.

The Sensitivity Domain

Sensitivity describes the ratio of output to input ofa particular process. In the context of irrigation,sensitivity analysis describes the behavior ofstructures during the propagation of transientconditions (the reactive process). The behavior ofregulation structures, such as offtakes andoutlets, in response to water level perturbations inthe parent canal, is the delivery sensitivity,described by the ratio of the relative offtakedischarge (dq/q) to the change in upstream waterlevel (�HUS), as described in equation 3.

(3)

All irrigation structures (offtakes, regulators,canal reaches) have a distinct sensitivity. Acomprehensive analysis of the sensitivity ofirrigation offtakes leads to the identification ofseveral indicators defining delivery andconveyance impacts, including upstream anddownstream translation of transients, as well as

water-level changes due to hydraulic conditionsand adjustment of structures (Renault andHemakumara 1999). Albinson (1986) has done anin-depth study of the relative sensitivity ofregulator and offtake combinations. The rationalefor sensitivity analysis is that more-sensitivestructure groups must be monitored and operatedwith greater care than less-sensitive groups.

An important consideration for canaloperations is the sensitivity of structures and theirimpact on the propagation or attenuation oftransient flows that enter the canal system. In theabsence of operational interventions the evolutionof perturbations through the subsystem defines adecay curve integrating the conveyance sensitivityof the reaches and associated regulators andofftakes. Systems with sensitive offtakestructures tend to attenuate the transient flows bydiverting surplus water through offtakes, whileless-sensitive structures propagate theperturbation downstream (Renault 1999a).

Determining the Demand for Operation

The study of the domains discussed aboveprovides the basis for the specification ofrequirements for operational interventions in aspecific subsystem. Before presenting a casestudy of the irrigation system let us consider asimple analysis of the operational requirements fora typical structure. For this simple case, adelivery structure (figure 2) links the parent canal,in which control is implemented, and thedependent canal, in which service is specified.

The vulnerability in the command area of thedependent canal defines the tolerance on thedischarge (here no consideration is paid totimeliness). For instance, if crops grown in thecommand area are sensitive to water deficit, thenlower tolerance, i.e., z in equation 1 should beminimized. On the other hand, if the drainagewater from the command area is recycleddownstream then the upper tolerance, y, can belarger. Having defined both tolerances (y and z),

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they are converted to precision of operation andcontrol through the sensitivity of the structure.Inverting equation 3, the precision required forcontrol in the parent canal (�HUS) is computed as:

(4)

where, y or z is substituted for � whenconsidering adequacy or efficiency. In this case yand z are specified as a tolerance in a lineardimension rather than a percentage deviation; S isthe sensitivity of the structure; and �HUS is therequired precision of control of water level in theparent canal.

Equation 4 expresses the target for the controlin the parent canal at this particular structure,which has to be converted into control targets atthe nearest downstream regulator. Control of waterlevels along the canal is the result of thecombined effects of the hydraulic properties of thecanal section, regulator characteristics, andperiodic operation of cross-regulator structures.The precision with which target water levels arecontrolled at cross-regulators (�H) is an indicatorof operational performance directly influenced by

management. Conversely, the extension of theinfluence of cross-regulators on canal water levelis determined by the physical characteristics ofthe reach and discharge rate defined by thebackwater curve.

The required operational precision isproportional to the specified tolerance andinversely proportional to the delivery sensitivity.Examples are given in table 2.

Equation 4 is valid for a single structure;however, similar relationships can be determinedat the system level by linking system sensitivityindicators, the required precision of control, andoperational performance (Renault 1999b).

The relationship between water service,irrigation performance indicators, and operationaltargets illustrated above for a simple case, can begeneralized, as shown in figure 3.

This relationship indicates that the requiredprecision of structure operations is the product ofthe tolerance on delivery and the sensitivity of thestructure. This relationship deals with the objectiveto achieve the specified service to the user.

Another important aspect of canal operationdeals with the management of perturbations(fluctuations of flows), with the objective of

FIGURE 2.Linking service and control through a delivery structure.

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increasing water management efficiency (forinstance rainfall harvesting) while minimizing theeffect of perturbations on the deliveries. Thiscombines the opportunities for perturbationmanagement (storage facilities or efficient use ofwater surplus) and the probability and magnitudeof occurrence. This allows the determination of theappropriate mode and frequency of operation,depending on the expected frequency ofperturbations as illustrated in figure 4.

Ultimately, the determination of the demandfor operation is a mixture of both quantitative andqualitative approaches. With the qualitativeapproach, the goal is to identify the significant

FIGURE 3.Functional relationships between the vulnerability, sensitivity, and the characteristic of the service.

TABLE 2.Examples of sensitivity, tolerance, and control precision.

Sensitivity of the structures Tolerance for discharge Precision of controlS � (�HUS)

(m-1 ) (%) (m)

0.5 ± 10% ± 0.2

Low sensitive ± 20% ± 0.4

1 ± 10% ± 0.1

Medium sensitive ± 20% ± 0.2

2 ± 10% ± 0.05

High sensitive ± 20% ± 0.1

properties strongly influencing potential operationalstrategies in each subsystem. These propertiesmay include, for example, the presence andopportunities for recycling losses and thevulnerability within the system. These propertiescan be combined to classify the demand foroperation as low, medium, or high and lead to amore appropriate distribution of efforts foroperation within the scheme. With the quantitativeapproach, formalized through equation 4, the goalis to specify the operational targets that will haveto be used for control to achieve the agreedservice.

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The proposed methodology has been applied tothe Kirindi Oya Irrigation and Settlement Project(KOISP), one of the largest agriculturaldevelopment programs in Sri Lanka completed in1987 (figure 5).

Scheme Summary

Kirindi Oya has two command areas withmarkedly different characteristics:

• The Old Ellegala command area existedprior to the development of the new system.The Ellegala zone is in a flat alluvial area ofabout 4,000 hectares. Water is delivered tothe area through an old system of fiveinterconnected tanks receiving water from adiversion structure (anicut) across the KirindiOya (river). Water is released from the newreservoir to supply this anicut system. TheEllagala command area has the first priority inwater allocations. The area is subdivided intotwo subsystems, designated as:

• Left Bank Old (LBO) 2,850 hectares, and• Right Bank Old (RBO) 1,150 hectares.

• The new command area was completed in1987. This command has a slightly undulatingtopography and is located upstream on bothsides of the alluvial plain of the Ellegalasystem. The new command is served by twosubsystems:

• Right Bank New (RBN) delivering to fivenewly developed sub-commands (Tracts 1,2 5, 6, and 7), totaling 3,300 hectares anda reservoir (Badagiriya) with an associatedcommand area at the tail of the maincanal. The Badagiriya command receivesscheduled deliveries from KOISP plussurplus flows from the tail of the maincanal.

• Left Bank New (LBN) canal commandarea, which is fully developed in Tracts 1and 2, and partly developed in Tract 3,with a command area totaling 1835hectares.

Climate. The climate is classified as tropicalhumid with two seasons: maha (a wet seasonbetween October and February/March); and yala (adry season from April to September). The averageseasonal rainfall is 750 mm in the maha season

FIGURE 4.Functional relationships between the vulnerability, perturbation, and operational modes.

Case Study of Kirindi Oya Irrigation Settlement Project, Sri Lanka

13

and 240 mm in the yala season. The annualevapotranspiration (ETref) is approximately1,500 mm.

Water resources and water management. Waterfor agriculture is derived from direct rainfall on ricefields and supplemented by releases from thesystem reservoirs. The main reservoir(Lunugamwehera, 200 MCM) was developed toextend irrigation to the new command areas andto secure irrigation double-cropping in the oldEllegala command. An important characteristic isthe cascade of tanks in the system that enablescapture of runoff, overflows, and drainage from

upstream areas to be used for irrigation at a laterstage of the season.

With limited commitments to downstreamuses (bathing and lagoon supply), KOISP can beconsidered as the last water user before the riverdischarges to the ocean; therefore, water savingsin this scheme are “real savings” as defined bySeckler (1996).

Crops. High-yielding varieties of rice are grownthroughout the project area during the mahaseason. However, during the yala season, only theEllegala area is routinely cultivated for rice withthe new command areas cultivating rice only when

FIGURE 5.Spatial evaluation of the demand for operation (KOISP).

Debara Wewa

Lunugamwehera

Reservoir

Ellagala Anicut

Pannagamuwa Wewa

Weerawila Wewa

BadagiriyaTank

I N D I A N O C E A N

Yoda Wewa

Tissa Wewa

Kirindi Oya

Right Bank

D4 very high demand

D3 high demand

D2 medium demand

D1 low demand

Distributary canal

N

Main Canal

Left Bank

Main Canal

14

water availability is high. Other field crops aregrown in limited parts of the new command areaon uplands during most yala seasons.

Institutional arrangements. The responsibility foroperations of the main and branch canals isvested with the Irrigation Department of Sri Lanka,a national public agency in charge of medium andmajor schemes in the country. The responsibilityfor operations of distributary canals was trans-ferred to farmers and/or associations of farmers inthe beginning of the nineties as part of an institu-tional reform. Farmers do not pay for water andthe activities (operation and maintenance) carriedout by the Irrigation Department are fundeddirectly by the government. Decisions aboutallocation of water are taken before the cropseason begins, by a cultivation committee withrepresentatives of farmers, state agencies, andother stakeholders. Decisions are based onavailable resources in the reservoirs and rotatingpriorities. In practice, the equity is maintainedfairly high within each subsystem (new and old)but it is low between the two subsystems, the oldarea receiving de facto a higher share than thenew area.

Improving System Performance

Due to a perceived mismatch between availableresources and potential uses of water the fullextent of the new command has not beendeveloped. Even though development is notcomplete, the cropping intensity in the irrigatedareas has not reached the expected levels andhas remained at about 178 percent (increasedfrom 140% before Lunugamwehera reservoir cameinto operation) in the Ellegala area and at only 108percent in the new commands. Current on-fieldoperational strategies are largely basedon “overflow” or paddy-to-paddy practices,which result in large outflows from the commandareas and losses where recycling is notfeasible.

Located in the coastal strip, KOISP shouldseek to maximize effective water use as anyunused water is lost to the sea. It can be shownthat the irrigation intensity at KOISP can be raisedto 200 percent in both new and old areas providedan efficiency of 43 percent is obtained at schemelevel (Renault 1997). In 1998, a water balancestudy showed that water losses to the sea areabout equivalent to the crop consumption throughevapotranspiration (Renault, Hemakumara, andMolden 1999). To achieve a high level ofefficiency, operational resources (human,transport, energy, communication) must beallocated effectively, which depends on anaccurate assessment of the required levels ofoperational control. The analysis of operationalrequirements at KOISP addresses two aspects:first, the water service required in the commandand, second, the management of reservoiroperations. In addition, specific operationalprocedures should be tested to improve theutilization of rainfall, aiming to harvest and storeas much rainfall in reservoirs and rice fields aspossible.

An analysis of the demand for operation atKOISP is presented, based on the frameworkproposed above, examining the vulnerability,perturbation, and sensitivity domains of the system.

Vulnerability Domain

Water is relatively abundant and annual averageresources (local rainfall + reservoir inflows) aresufficient to sustain two crops a year provided thesystem is operated effectively (Renault 1997).Maha rainfall is reasonably dependable; however,yala rainfall is less so. The start of irrigation in thenew areas generated some concerns in the earlynineties related to the leaching of salt that drainedto the downstream area (old system). However,the phenomenon has not persisted and, apart fromsome limited areas very close to the sea, nomajor salinity or waterlogging problems are foundin the area.

15

The existence of a cascade system, withseveral tanks in succession, makes it possible forthe scheme to be very efficient in harvestingrainfall by operating the tanks at the lowest levelpossible to maximize storage capacity.

Single bank or contour canals (SBK) arecommon in Sri Lanka giving the potential tocapture runoff from lateral watersheds. The RightBank Old (RBO) canal is a single bank contourcanal and this, combined with the storagecapacity of three intermediate reservoirs, providesopportunities to capture water during rainy periods.Some parts of the Left Bank New (LBN) canal arealso single bank.

Water management. The potential for recyclingdrainage or spilled water from the command areasdivides the scheme into two operational catego-ries. All tracts in the LBN canal and Tracts 1 and2 of the RBN canal drain to tanks that supply theEllegala area. Tracts 5, 6, and 7 of the RBN canaldrain to a lagoon and ultimately to the sea,resulting in large water losses. Drainage flowsfrom the RBO subsystem return directly to themain river canal and then to the ocean with littleopportunity for recycling these losses exceptthrough pumping facilities.

The Left Bank Old command area ischaracterized by extensive interconnectionsbetween drainage and irrigation networks due tothe flat topography. It is almost impossible todefine precise command areas for individualoutlets (Mallet 1996) or to uniquely characterizethe hydraulic characteristics of channels orstructures. Surplus flows at one point becomeinputs elsewhere; therefore, in the terminologydeveloped by Renault and Godaliyadda (1999),this area is classified as a return-flow system.The LBO subsystem must, therefore, be managedas a single unit considering several entry points tothe network such as tank outlets and canal inletsand a number of drainage outlets to the river andthe ocean. To increase the efficiency of wateruse, all drainage outlets require monitoring toavoid excessive losses. An effective feedback

control system is essential to enable effectivecontrol of the inlets into the subsystem. There isno conjunctive use in the area and pumping fromthe river and drainage or irrigation canals isrestricted to small-scale gardening enterprises.

Multiple uses of water are important in theKOISP area. However, there are no major conflictsbetween irrigation and the other uses of water,including domestic water supply, bathing,homesteads, gardens and perennial vegetation,environmental uses (wetlands, wildlife habitat),tourism (lagoons and national parks), andfisheries. Irrigation is the major user of water,representing more than 90 percent of water use inthe basin; and water for irrigation ensuresavailability for other uses. There are no specifichealth-related issues.

Agriculture. Rice cultivation is relatively lessvulnerable to variations in water supply than otherfield crops due to the buffer effect of the floodedrice field. As the area is mainly cultivated for ricein both seasons, the cropping system can beconsidered as homogeneous and of low vulnerabil-ity. This is an important characteristic for tractswhere recycling is not feasible as it may allowimplementation of strategies to reduce overflows.Special consideration may be required for the newareas, where some farmers cultivate other fieldcrops that are more vulnerable to water shortages.

Soils in the Ellegala area are heavier thanthose in the new command areas. Percolationrates in these two areas are estimated at 3 mm/day and 6 mm/day, respectively (IIMI 1994).Although this has some implications for waterallocation and drainage flows it has little impact onoperational strategy or on system efficiency, asthe dominant criterion is the ability to recyclewater.

Water rights and equity. In theory, all farmers atKOISP have equal water rights. However inpractice, farmers of the old areas have estab-lished a powerful position and have been able toestablish preferential allocations of water in their

16

favor. The Ellegala area also obtains irrigationsupplies in advance of the new areas, directlycontrary to effective water savings strategies.Under these conditions, any attempt to improvewater management must assure 200 percentirrigation intensity to farmers in the Ellegalasubsystem before attempting to implement anychanges of supply to the new areas.

Environment. The area surrounding KOISP hasseveral facets of environmental and wildlifeimportance: The entire area is a recognizedwetland sanctuary of importance to migrating birdsand the Bundala National Park is to the southwestof the scheme (Matsuno, van der Hoek, andRanawake 1998). The lagoons in the park arepartly supplied by water draining from the RBNarea. Fortunately, there are no conflicts betweenimproved irrigation management and existingenvironmental concerns. Improved water manage-ment in irrigated areas will extend the period ofwater in the tanks and will reduce freshwaterinflows to the lagoons, currently considered apotential hazard.

Water service and performance indicators. Insubsystems with no opportunities for recycling ofexcess flows, the water service must be muchmore accurate than elsewhere. Therefore, toler-ance on deliveries (equation 1) must be minimizedand a feedback link between drainage outflowsand system inlet settings should be established.In areas where recycling is possible, the waterservice can be less precise and delivery tolerancecan be less strict in terms of discharge providedthat, in the long term, the volumes are roughlyadequate. A feedback loop control is recom-mended to maximize storage potential in down-stream tanks during the wet season.

Perturbation Domain

Analysis of this domain focuses on theoccurrence and magnitude of externally and

internally generated perturbations. The upstreamboundary conditions of each subsystem arehomogeneous as all systems are supplied fromthe main reservoir or tanks and have manuallyoperated gates.

Lateral flows. The RBN and LBO canals aredouble bank canals and as such not greatlyinfluenced by rainfall. Parts of the LBN and theentire RBO canals are Single Bank Canals (SBK)and, therefore, susceptible to large perturbationsduring periods of rainfall.

Position in system. Field observations haveconfirmed that the LBN and RBN canals weresubjected to an increasing range of water-levelfluctuations from head to tail locations, increasingfrom 65 mm at the head to 90 mm in the middlereaches, and then to 110 mm at the tail duringmaha 1993 in the LBN. Observations on the RBNshow a similar trend; records over six seasonsindicate that the average water level fluctuationsrange from 75 mm at the head to 120 mm at thetail.

Users. Discipline is variable between the systems.In the old system there are few disciplinaryproblems, probably as a result of the relativelyreliable water supply. In the new system, farmersmust contend with shortages of water to theextent that some have not been able to establishthemselves as farmers and have had to seekother employment. Even those who have beenable to establish themselves as farmers have lessinfluence in decision making over water alloca-tions. As a result, unauthorized operations ofgates and harmful interventions at cross-regulatorsdo occur. System managers have responded byissuing more water to the main canal than istheoretically required. The lack of discipline maybe a serious constraint to increased precision inoperations aimed at improved efficiency andtherefore intervention strategies should be aimedat achieving highly reliable water supplies in allareas.

17

Operational procedures. To improve economy ofwater use in command areas with no opportunityto recycle drainage flows, managers will have toencourage farmers to adopt field procedures thatare more effective than the existing lot-to-lotirrigation. Two alternative main canal operationalprocedures might be considered: first, a strategyof progressive reduction of deliveries; and second,the introduction of rotational delivery. Progressiveadjustments (PA) would impose permanent andprogressive modifications of inflows (deliveries) tocontinually reduce downstream drainage dis-charges. This option would require precise opera-tion and methods to fine-tune deliveries to mini-mize inflows, while avoiding drying-up of down-stream field units. Ultimately, this method wouldresult in a minimum steady state discharge.Rotational operations (RO), either with an on/offschedule, or with alternating high and low dis-charges, will result in frequent fluctuations in canaldischarges, requiring greater supervision of thecanal system.

The Sensitivity Domain

Offtake sensitivity. The sensitivity of offtakesdistinguishes the RBN canal (medium sensitivity,average S=1.3) from LBN and RBO that areclassified as highly sensitive (respectively average= 2.4 and 2.2). This means that the same level ofprecision in water depth will generate dischargedeviations twice as large in LBN and RBO than inRBN.

Regulators and reaches. Three different situ-ations can be distinguished with regard to theregulation of water levels in the main canalsas listed below:

Not regulated: for example, the RBO canal is notregulated effectively as the density of regulators is

very low and most existing structures are nolonger functional.

Poorly regulated: the LBN canal has adequateprovision of regulators, but the existing conditionis poor, with gates generally missing or otherwiseinoperable.

Well-regulated: the RBN canal is well-equippedfor regulation and the regulators are in goodcondition.

Spatial Variation of OperationalDemands at KOISP

The operational requirements to achievespecified levels of water delivery service andacceptable levels of water use economy atKOISP are analyzed for daily regulation of waterreleases and for control of the canal system.Requirements for improved scheme operationsrelated to the scheduling and tank managementto impose rainfall-harvesting tasks are notaddressed here.

Considering four classifications of operationalrequirements, varying from low demand to veryhigh demand (D1, D2, D3, and D4), fivesubsystems were identified. An evaluation of thecharacteristics of the demand for operations ineach is summarized in table 3. Although theranking used here may be subject to discussion,the identification of significant operationaldifferences at each subsystem allows a spatiallydifferentiated allocation of management resourcesas shown in figure 5.

The next step would be to determine whatallocation of resources would be required to matchthe demand. Clearly, the number of operatorsrequired will vary from area to area to match theoperational demand that would, in turn, improvethe overall efficiency of the system.

18

TABLE 3.Evaluation of the demand for operation per subsystem in KOISP.

Subsystem Tracts 1 and 2 LBO LBN RBO Tracts 5, 6, and 7 of RBN

of RBN

Vulnerability Low Low Low Very high Very high

Recycled Return-flow RF Recycled Non-recycled Non-recycled

Water service* Low Low Low Very high Very high

TOL Q = ± 20% TOL Q = ± 20% TOL Q = ± 20% TOL Q = ± 5% Option PA*** TOL Q = ± 5%

High

Option RO**** TOL Q = ± 10%

Sensitivity of structures High Very high Very high Very high High

1.3 (not measured) (2.4) 2.2 1.3

Precision Low High High Extremely high High ± 4 cm for option PA

± 15 cm 10 cm as an indication ± 10 cm ± 2.2 cm Medium ± 8 cm for option RO

Unrealistic

Perturbations Low probability Low probability Medium probability High probability and magnitude High probability and magnitude

Low magnitude Low magnitude (High sensitive offtakes (No water depth control; single (Improved operational

and Single Bank Canal bank; improved operational procedures)

sections) procedures)

Operational mode Low frequency Medium frequency High frequency checking Note: A specific control project High frequency FBC from

and frequency FBC** from FBC from drainage of sensitive offtakes will have to be designed for drainage outlets

downstream tank outlets Low frequency FBC from RBO including some rehabili- Precise control of level

downstream tanks tation and/or modernization (Improved operational

works. procedures)

Class of demand D1 D2 D3 D4 D4

Low Medium High Very high Very high

*The tolerance for time is irrelevant here as deliveries are continuous.

**FBC: Feedback control: monitoring downstream discharge or variation of volume and operating upstream issues.

***PA: Progressive adjustments.

****RO: Rotational operation.

19

The case study of Kirindi Oya illustrates theexistence of heterogeneity of requirements foroperational resources, even within a medium-sizedmono-cropped irrigation system, based on ananalysis of three operational domains:vulnerability, sensitivity, and perturbation.

System managers can address heterogeneityof operational demands through two differentstrategies. They may accept the reality ofspatially variable operational requirements andallocate resources accordingly. Alternatively, the

effects of spatial variability can be minimized byinterventions in the physical system. In eithercase, it is expected that the improved evaluationof the spatial variability of demands for operationwill be useful in the design of:

• more cost-effective strategies and proceduresfor operation, and

• priorities for rehabilitation or modernization ofphysical infrastructure.

Conclusions

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Research Report

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Modernizing IrrigationOperations: Spatially DifferentiatedResource Allocations

D. Renault and I.W. Makin

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