DEVELOPMENT OF RUNOFF CONTROLLED RAIN GARDENS AND A STUDY OF ITS EFFECTIVENESS

Abstract

 A rain garden, which functions as runoff control by rainwater storage and infiltration, draws attention as a Green Infrastructure technology in an urban setting. This study developed a rain garden in a Community Café and a Detached House in Fukuoka City, with the goal of 100% runoff control of rainfall exceeding the Fukuoka City sewerage plan. After implementation, we conducted on-site inflow tests and water balance monitoring to compare the estimated values of the design with the actual runoff control effects. As a result of the inflow test in the Café, the runoff per unit time was 0 mm, which means that the water could be stored for more than 130 mm against the estimated water storage height of 100 mm. At the Detached Houses, we observed runoff from the rain gardens, focusing on the daily rainfall of 297.6 mm that occurred during the monitoring period. As a result, the observed runoff was about 0.24 mm, compared to the estimated runoff of 7.9 mm. Therefore, the rain garden designed for infiltration and storage was found to be highly runoff control effects against heavy rainfall.