Abstract
In recent years, in order to utilize paddy fields as temporary water holding areas for eupotamic life such as fishes, installation of fish passes from farm drains to paddy field lots has been tried. However, since many farm drains are deep, the paddy field fish pass often must be enlarged. Enlargement of a fish pass not only causes a jump in environmental spending, but the large numbers of fish place a burden on natural resources. In this paper, a policy for reducing the difference in level between a farm drain and a field lot based on the following measures is proposed as a way to help downscale the paddy field fish pass. The first measure is gently sloping the sublateral drains, the second is separation of surface drainage and subsurface drainage, and the third is installation of lateral drains in each field block unit. Moreover, it is shown that these measures result in the related effects of reduced areal shrinkage, curtailment of weeding area, and improvement in the safety of farm operations. Since the proposed reduction in level differences has a high correlation with the completion of land consolidation, its validity as an environmental measure is predicted.
