Regional Ecosystem Modeling and Assessment of Near-Natural Engineering for Irrigation and Drainage Canals and Irrigation Ponds

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1.The studies in the irrigation and drainage canals in the alluvial fan of the Tedori river and the area around the Khokugata, Ishikawa, Japan, suggested that flow velocities and relevant factors such as water temperatures and sediment thickness have an impact on the diversity and the distribution of aquatic creatures in the canals. Then, another study on benthic animals in small canals, suggested that the species richness of benthic animals correlate closely with the diversity of flow velocities. The studies revealed the importance of increasing the diversity of flow velocities in canals and improving fish-ways at drop structures, in order to maintain the biodiversity in irrigation and drainage canals.2.Mass balance of nutrients in the Higashiike, Minakuchi town, Shiga Prefecture, was discussed. The study suggested that 7.5% of nitrogen and 30% of phosphorus in inflow are accumulated in the pond and 70% of phosphorus accumulated in the pond is fixated by phytoplankton.3.Effectiveness of fish ponds (0.5m depth and 20m length) constructed at intervals of 500m, at the base of the Ohe Drainage Canal, Aichi Prefecture, was examined. The studies suggested that (i) the fish pool provides habitat for fishes particularly when irrigation was not being done, (ii)it is not easy for small fishes to migrate from one fish pond to another fish pond, and (iii) flow velocities in fish ponds are not small during the irrigation period According to the results, installation of fish-shelter-blocks and conservation of aquatic plants were proposed in addition for the Ohe Drainage Canal.4.The surveys on plankton and chemical properties of water were conducted in the Hangaike at the campus of Gifu University. Based on the survey results, the model for predicting the population movement of plankton was established by using cellular automation. The model showed the possibility for predicting the population movement of plankton by this method.