The Water Quality and Its Criteria for Upland Irrigation System

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The contamination of blue-green algae from euntrophic lake or river into upland irrigation system has caused degradation of water quality which will bring about various disturbances for proper operation. In order to establish the design criteria to cope with this difficulty, we carried out the following collaboration.(1) In order to analyze the present situation of water quality degradation in the irrigation system, major items of water quality and flow rate were measured systematically for the case of Kasumigaura Irrigation Project. Statistical analysis on the relation between each items clarified the dynamic process of change of water quality during its transportation through the system. On the basis of this result, allowable concentratioon of Chl-a which can be regarded as the most important index of blue-green algae was estimated.(2) Effects of the quality of irrigation water on the grows and yield of common buckwheat were examined under pot culture in the green house. The result showed no significant change.(3) Hydraulic properties of blue-green algae colony, i.e., the density of algae cell and basic consumption of oxigen were determined by a series of experiments. The obtained value will provide useful information s for the estimation of water quality load and removal efficiency of blue-green algae.(4) The applicability of water treatments by means of an ozonation, an UV radiation and an addition of tannicacid to prevent or to reduce the blooming of algae were examined. Biological activity after treatment were expressed as a function of radiation intensity and elapsed time. It was found that the formation of a floc has remarkable influence on the survival of blue-green algae.