Availability analysis of irrigation systems for improved operation and management.

Abstract

Operation and maintenance of irrigation-water-delivery and distribution systems is an essential element for sustaining agricultural production. Few obvious benefits from irrigation system maintenance may be one reason funding is often insufficient. The lack of an accepted, standard procedure of requesting maintenance funding contributes to this problem. Regular monitoring of flows can demonstrate the effect of maintenance events on irrigation system performance. A simple maintenance framework has been developed for use by irrigation system managers in Nepal that monitors the effect of maintenance events on system flows. The framework can be implemented as a step-wise program for monitoring flows. Initial monitoring points are suggested as the intake and head of each branch canal. Additional flow measurement points can be added as needed. The framework defines two maintenance objectives and uses two levels of classification to define six types of maintenance. Six maintenance activities and decision criteria are suggested. Other maintenance activities can be defined and described using this format. Budget request and report forms are developed using actual maintenance event examples on three agency managed systems in Nepal. These examples manifest the expected and actual impact of maintenance events on water deliveries. A methodology based on crop water requirements is developed to set decision levels for maintenance activities that result in increased water deliveries. Availability is defined as the ratio of time of successful system operation to total desired operation time. Operation is successful when the amount of water supplied exceeds a given percentage of the lesser of crop water requirements or design flow. Thus, availability provides adequacy and dependability information about water delivery related to the needs of the crop. Furthermore, this ratio can be decomposed into unavailabilities signifying the percentage of time low flow was caused by various problems. This is valuable information for improving water delivery performance. Over 12 crop seasons availability varied from 0 to 0.90 in three Nepal irrigation systems. Canal capacity less than crop water requirements was the greatest reason for unavailability during the monsoon season. Insufficient water supply was the greatest reason during other seasons.