ANALYSIS OF EFFECTS OF WATER BANKING USING A WATER CYCLE ANALYSIS MODEL －AN EXAMPLE OF THE ZUIBAIJI RIVER BASIN, IN FUKUOKA, JAPAN－

Abstract

 The Zuibaiji River basin in Fukuoka Prefecture has a rich natural environment and is ecologically valuable. On the other hand, there is a concern about decreasing in groundwater recharge due to urban development and reduction of paddy fields. Water banking has been experimented as a solution to these possible problems. In this study, the characteristics and effects of water banking under several conditions were verified by conducting a water balance analysis in the Zuibaiji River basin, assuming that water banking is applied to wastelands such as fallow and abandoned fields and non-cultivated paddy fields. As a result, the difference between water banking on wasteland and paddy field, and the difference in the location of water banking were revealed. It was also confirmed that water banking can increase groundwater recharge by 7%, decrease surface runoff by 15.5%, and store 7% of total surplus surface water underground in the entire Zuibaiji River basin regardless of land use conditions. Also, in common with all conditions, the freshwater level increases significantly immediately after water banking. However, the speed of return to the original water level is also fast during the period when water banking is not conducted. On the other hand, as for the saltwater level, the range of change in the water level immediately after water banking was small, but it decreased from the original saltwater level the longer it was implemented. Furthermore, it was found that the surface runoff rate of the surrounding area was uniformly low per grid, and the water level improvement by water banking was more effective for the land with higher runoff coefficient. The results obtained from the analysis of water banking in this study will contribute to the countermeasures against environmental problems such as sea level rise and precipitation decrease.