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  Irrigation Management / Planning & Rehabilitation
 

R Number:  R5832
Contractor:  HR Wallingford
Dates:         1992/92 to March 1996
The project developed a structured field methodology for use in pre-feasibility field studies which guides diagnosis of system performance and the identification of hydraulic, agronomic and economic factors that limit performance.

Executive Summary
Objectives

  • Purpose
    To develop a methodology to assist in planning of rehabilitation and modernisation of irrigation schemes.

  • Outputs
    1. A method to identify what schemes or parts of schemes require rehabilitation or modernisation.
    2. A checklist or other procedure to identify and categorise causes of poor performance.
    3. A ranking procedure based on potential benefits from rehabilitation developed and field tested.
    • Methodology

    Field studies in Indonesia evaluated a number of different approaches potentially capable of diagnosing system performance and identifying key constraints. The methods evaluated were:

  • Use of routinely collected hydraulic and agricultural data to calculate performance indices at several locations within a scheme
  • Use of a hydraulic model to simulate present conditions and possible interventions
  • Use of checklists and field surveys to identify the extent and severity of under-performance within the scheme and their underlying causes.
    • Results

  • Operational data from three schemes in Indonesia were analysed to identify temporal and spacial trends in hydraulic and/or agricultural performance within a scheme and identify the locations limiting performance. On the schemes analysed, the methods failed to give more detailed insight into hydraulic or agricultural performance than could be obtained from direct inspection linked with information provided by operations staff. The quality of available data was generally poor and the calculation of a minimum set of indicators at several locations within the canal network required extensive data processing.

  • The use of a hydraulic model to identify hydraulic constraints and quantify the impact of different physical rehabilitation measures was evaluated on two schemes. Good survey data were available for the systems which were relatively small (3500 and 900 ha) and characterised by steep slopes. The large number of drop structures effectively broke the canal systems into numerous, hydraulically independent units where problem diagnosis could be achieved without recourse to detailed modelling. It was concluded that modelling could serve as an aid to rehabilitation planning only on larger, complex systems on flat terrain where canal survey data are available or where survey costs would represent a small percentage of the expected rehabilitation budget. The use and operation of an hydraulic model requires good hydraulic and computational skills and reliable field data.

  • A diagnostic procedure was developed consisting of three components:
    - Checklist of performance constraints - intended to detect the nature and approximate scale of constraints, both technical and non-technical, on the performance of a system. Underlying causes of apparent constraints should be identified in the process. It should serve as the basis for initial discussions with O&M staff during pre-feasibility investigations and as a guide to further work.
    - Farmer questionnaire - provides information from field level about the functioning of the system, the needs for technical improvements, general problems faced by farmers and the relative importance of technical and non-technical issues. In conjunction with the checklist it provides a crosscheck on initial findings.
    - Function-based Condition assessment, the third principal element of the Procedure Assessment would be undertaken at feasibility stage if the checklist and questionnaire indicate that there are physical constraints to improved system performance. The process is intended to establish a consistent basis for determining the fitness of an asset for its function.

    The priority of works is established by combining the assessed condition of a component of a system with a measure of its strategic importance and the area served, in an overall score and ranking. The cropped area served by an element is considered to be a rough proxy for its economic value to the system, and it is therefore included in the priority-setting process. As it is difficult to link benefits uniquely to the improvement of individual components of an agricultural system, optimisation of the returns to packages of works is not attempted. However, ranked lists of works will form the basis for detailed economic analysis of the costs and benefits of possible alternative programmes of investment.

    • Conclusions

    Rapid methods for comparing between schemes or identifying 'hot spots' within schemes based on analysis of routinely available irrigation operations and agricultural data were shown not to be practicable. On schemes were sedimentation is identified as a major constraint, modelling must incorporate sediment routing in order to identify the immediate and longer term impacts on sediment deposition of any proposed intervention.

    The checklist and ranking procedure have been successfully developed. The linking of individual physical R&M actions to a measure of benefit (normally financial/economic) was not resolved in this project. Calculation of current and predicted flows can be used to gauge benefit in terms of a hydraulic performance indicator, but this may be of limited value to project planners.

    Further Information
    List of Publications

    Cornish, G 1994. Methodology to facilitate cost-effective Rehabilitation and Modernisation of Irrigation Schemes. Interim Report. OD/TN 68 HR Report

    Cornish, G. and Skutsch J. 1997. A Procedure for Planning Irrigation Scheme Rehabilitation. OD/TN 84 HR Report

    Improving Irrigation Prospects. Research Focus No.28 February 1997.

    Follow-up Activities

    Procedures developed in the course of this project, relating to the assessment of physical infrastructure, will be promoted further under Project No R6260, Aids to Maintenance of Irrigation Systems.

    Contact Details for Further Information
    DFID KAR WATER Dissemination Officer
    HR Wallingford
    Howbery Park
    Wallingford
    Oxon. OX10 8BA

    Tel: +44 1491 835381
    Fax: +44 1491 826352
    Email: dfid-kar-water@hrwallingford.co.uk

     

    Project Manager
    G.A. Cornish
    Email: gac@hrwallingford.co.uk