ESTIMATING GROUNDWATER LEVEL CHANGES BASED ON LAND SUBSIDENCE IN THE ISHIKARI RIVER BASIN

Abstract

 It has been 100 years since the flood prevention works began in the Ishikari river basin, the northern island Hokkaido in Japan. The purpose of this activity was to reduce groundwater levels up to 90 cm in addition to the flood control management because many regions in the Ishikari river basin were covered by peat and wetlands. This study investigated the change of groundwater level in association with historical information of land subsidence and field observation over some areas of paddy field where were used to be natural ponds or wetlands. The estimation method for the change of groundwater level was applied to a method which was used to investigate embankment subsidence in peat lands. Our results showed that the estimated change of groundwater level at several areas is comparable with observed values by our field survey.