Abstract
In the Ashigaike Regulating Reservoir, not the runoff from the watershed but the conveyed water from the outside of watershed is stored for the improvement of the water quality and the strengthening of the irrigation water supply ability. In this reserch, the method not only to decrease TN load but also to preserve the effect of dilution by water conveyance was considered by simulation using distributed water quality tank model. As a results, it was clarified that the following methods are suitable; 1)Water conveyance would not be executed until the storing rate of the reservoir decreases an appropriate value. 2)The runoff water from the watershed would be stored. 3)Reuse irrigation would be executed. 4)The water which equals the volume saved by reuse irrigation is conveyed and released during non-irrigation period.
