九州大学大学院農学研究院生産環境科学部門地域環境科学講座水環境学研究室
Laboratory of Drainage and Water Environment, Division of Regional Environment Science, Department of Bioproduction Environmental Science, Faculty of Agriculture
九州大学大学院農学研究院生産環境科学部門地域環境科学講座水環境学研究室
Laboratory of Drainage and Water Environment, Division of Regional Environment Science, Department of Bioproduction Environmental Science, Faculty of Agriculture
The flood mitigation function of agricultural land in the Chiyoda district of Saga Prefecture, Japan, has been quantitatively evaluated using numerical simulations. This district is located on a flat low-lying area along the lower reach of the Chikugo River, characterized by paddy fields with a network of creeks and drainage to the tidal compartment of the Chikugo River. Generally speaking, agricultural land has a function, such as that of a reservoir, which temporarily stores up storm flow during floods. This flood storage effect for agricultural land, which is known as the flood mitigation function, is one of the many important functions for country's conservation that has been in effect since the beginning of agriculture itself. First, a paddy field basin model was constructed based on the present condition of the Chiyoda district and an upland field basin model and an urbanized basin model were introduced under the assumption that paddy fields of the Chiyoda district would be converted into upland fields and urbanized areas. Second, the difference in flood runoff characteristics caused by land uti}ization, the creek area ratio, and the existence of optimal control of drainage facilities, was evaluated using the basin models from the viewpoint of flood mitigation. Finally, an indicator to estimate the flood mitigation function of agricultural land in a flat low-lying area in a large scale view, that was proposed by the authors in the previous paper, was examined in the Chiyoda dist,rict. It was concluded that the flood mitigation function of a flat low-lying agricultural area was evaluated by the macro-indicator MI, consisting of three sub-indicators, i.e. 1. for the land utilization, lp for the creek area ratio, and lr for the optimal control of drainage facilities.