Canals 29 Chapter 5 Maintenance and repair works 5.1 INTRODUCTION This chapter describes why and how a canal system should be maintained. The chapter also looks at some of the most important repair works in connection with canals. The performance of an irrigation canal system depends not only on how the system is operated, but also on the condition of the canals. Irrigation canals function well so long as they are kept clean and if they are not leaking. If no attention is paid to the canal system, plants may grow and the problem of siltation may arise. Even worse, the canals may suffer from leakages. Plant growth and sedimentation not only impede the flow in a canal, they also diminish the area of the cross-section. As a consequence, the canal capacity may diminish (see Section 3.3). A reduction in the capacity may result in overtopping and a limit on water supply to the fields. The available water will also be reduced when there are leakages in a canal. To protect the system from these problems, the canals should be maintained on a regular basis. It is not just the smaller, tertiary irrigation canals that need to be maintained, it is the primary and secondary canals as well. Sometimes these canals may be located far from the farmers’ fields and this can be one reason why farmers show no interest in maintaining them. However, the smaller canals receive water from these canals and so maintenance of the larger canals is of vital importance for the proper functioning of the whole system. Even when a canal is well maintained, serious technical problems may arise. These problems need to be solved by repair or improvement works. A repair should usually be done as soon as possible, depending on the severity of the problem. Improvements, such as the lining of a canal section, may be postponed until the end of an irrigation season, when canals are dry and farmers have more time available. After a serious problem is found on an inspection tour, a team of workers or farmers should be available for repair as soon as possible. Such a team should be formed at the beginning of the irrigation season in order to have it on call in case of emergencies. The same team may be asked to do the improvement works. If necessary, a contractor may be asked to do the job. 5.2 CANAL MAINTENANCE A good maintenance programme can prolong the life of canals. A routine, thorough programme should be kept to. Maintenance of an irrigation canal system is usually carried out in between two irrigation seasons, or at times of low water demand. It consists of cleaning, weeding, de- silting, re-shaping, and executing minor repairs.