河道特性を反映した中小河川管理に向けて−千葉県夷隅川支川落合川を例として−

抄録

The Isumi river basin was formed on the so-called Kazusa stratum consisting of silt, sand and mud layers by the upheaval of the sea bottom in the tertiary period, and the alluvial plain was formed by burying of valley associated with the sea level rise. The Isumi River has formed several river terraces and erosion channels by meandering and erosion in the alluvial plain. The short-cut of the stream called "kawa mawashi" has been carried out to create new paddy fields and to prevent the floods due to meandering, and measures for straightening the channel have been carried out, resulting in downstream bank erosion. The characteristics of this river have been investigated through the field observation from the upstream of the Ochiai River up to the mouth of the Isumi River while using past aerial photographs. Important notes for the management/planning of a small river were proposed.