Irrigation Canal System Survey

Abstract

AbstractBased on the concept of establishing a continuous water flow and material cycle in a watershed, it is important to connect an irrigation canal system from the river to the drainage canal system and back to the former river. Even if biomass increases only in the drainage canal, the effect is limited. To enrich biodiversity in paddy fields, year-round water flows and natural materials in canal beds are important. However, information on the water volume that contributes to the environment and conserves paddy ecosystems is extremely limited. Therefore, we must address the technical issues related to water flow. The purpose of this study is to show the ecological significance of connecting irrigation and drainage canals in a consolidated paddy field and provide a practical plan based on a field survey of fish distributions at four sites in a paddy field in Shimodate City (now Chikusei City), Ibaraki Prefecture, Japan. The sampling interval was one week during May 2002 to June 2003. The results were the following: (1) the ten species of fishes caught in the canals were classified into two groups, fishes living mainly in drainage canals, such as Misgurnus anguillicaudatus and Silurus asotus, and those living in both irrigation and drainage canals, such as Gnathopogon elongatus elongatus. (2) The first group of fishes are distributed in the drainage canal system and move to paddy fields to facilitate movements between these two areas and expand their spawning grounds and habitats. These fishes are called ‘drainage–paddy field fish.’ The second group of fishes are distributed in both the irrigation and drainage canal systems, and it is important that movement is facilitated between the irrigation and drainage canal systems, which would also habitat. These fishes are called ‘irrigation–drainage fish.’ (3) An effective way to attain both fish conservation and high productivity is to employ a shallow farm drain by using an underdrain system for subsurface drainage. The small difference in elevation between farm drain and paddy plot allows the first group of fishes to enter the shallow water in the paddy field, and the connection of the main canal and shallow farm drain through water flow allows the second group of fishes to move between the irrigation and drainage canals. (4) As a fish conservation measure that can be conducted immediately, the fish that exist in the irrigation canal in the irrigation season can be moved to the shallow farm drain from the main canal before stopping the water flow for irrigation.KeywordsDrainage canalFarmland consolidationFishIrrigation canalPaddy fieldShallow farm drain