Author(s): M. Sasaki; T. Takeuchi
Linked Author(s): Mikio Sasaki
Keywords: River Mouth; River Blockage; Stability Condition; Inlet; Estuary
Abstract: The mouth of River Iwaki is characterized by the present Mitoguchi channel and inlet. In the present study, the history of Mitoguchi channel blockage and stability conditions of Mitoguchi channel was investigated. The following conclusions were derived. (1) The blockage of Mitoguchi channel had the case to become blockage after the mouth of a river moved to the south and the case to become blockage after moving to the north. The cases to become blockage as the mouth of river moved to the south are a little a lot. However, there was 30 percent or more occurrence frequency when the river moth was blockaded after the mouth moved to the north. The river mouth had become blockage without moving to the south or to the north. (2) Preventing the blockage of a river mouth became possible just when the pier's in the south and north both shores were constructed in the Mitoguchi channel. (3) Comparing with the shoreline in 1938, the shoreline retreats in the south and north both shores, and the average distance of the retreat in the range of 500 m from the pier becomes 30m in the south shore and 20m in the north shore. It is balanced as a whole as the advancement and the retreat are repeated since 1965. (4) Maximum flow velocity at the Mitoguchi channel reaches to 0.5-0.6 m/s as the sea water level difference becomes 30-40cm, the velocity becomes 0.4-0.5 m/s as the tide level difference is 20-30 cm. Those flow velocities have power by which the coastal sediment which has entered into the Mitoguchi channel are swept up. (5) The flow section area of Mitoguchi channel reaches a stabile flow section area, then, even if the change of the section shape in year is seen, the section area is hardly changed. The water depth in the shallowest part in the Mitoguchi channel is 2m or more. The water depth of 4m is kept in front of the Mitoguchi channel. (6) The average depth of the waterway in the Mitoguchi channel has continued with 3m or more. This is due to the excellent relation between the on/off sea flow velocity that has power to sweep up coastal sediment from the channel to sea and the size of littoral drift.
Year: 2003