Operation of Regulating Reservoirs in Irrigation Canal Systems to Improve Upstream Water Delivery Flexibility

—Case study on a paddy irrigation district in the Tohoku region—

Abstract

In the study area where regulating reservoirs are located between open-channel sections and pipeline sections, the authors evaluated how those reservoirs affect irrigation flexibility upstream from them as well as downstream. The local Land Improvement District (LID) reduces scheduled flow rate for the reservoirs' service areas and then redistributes the reduction to open-channel's areas. This increases the scheduled flow rate in the open-channel's areas up to around 20% compared with the overall mean, thus it can be interpreted that irrigation flexibility is improved there. In daily operations, the LID attempts to minimize inflow for one of those reservoirs so as to maximize the water availability upstream. And occasionally, the LID increases the inflow depending on the situation such as rapid drawdown of the reservoir. This operation strategy can additionally increase the irrigation flexibility throughout the district. With this strategy during periods when the water demand is highest, the reservoir was used to absorb temporal flow mismatches over 24 hours or more, unlike the general principle for regulating reservoirs.