Suburban Agriculture and Long-term River, Groundwater, and Soil Moisture Changes Achieved by the Hokkaido Comprehensive Development Plan in Lowlands Around the Chitose River Basin

Abstract

　This study demonstrated the co-benefit of river management projects for both flood control and improvement of suburban agriculture farmland in the basin with long-term data of the river water level, ground water level, and soil moisture conditions (NDWI) in lowlands around the Chitose River Basin. Results show three main factors affecting the development of suburban agriculture: (1) The river flood control projects drastically reduced the frequency of inundation and associated soil runoff from farmlands during floods. (2) The projects also reduced river water and ground water levels during ordinary water discharge, leading to improvement of wet conditions in peat swamps around the midstream area of the Chitose River (KP22 km − 28 km). (3) Adding drainage improvement through agricultural land projects has greatly improved farmland soil wetness. Agricultural production diversity was achieved in the basin. Although record-breaking rainfall has not been confirmed for about 40 years, attention must be devoted to changes in future rainfall characteristics.