洪水に伴う利根川感潮域の底質変化

抄録

Field surveys were conducted in the Tone river estuary to examine the bed material change by floods. Bed materials were sampled at several points along the deepest line of the channel before and after the floods, and grain size distribution and ignition loss was analyzed for the samples. The analyzed data showed that the bed material before the floods was mainly composed of fine sediment having the mean diameter of about 1Oμm, however after the large scale flood with the peak discharge of 8000 m³/s, the bed materials changed into fine sand having the mean vales of around 200μm in the whole estuary. Furthermore, the data also showed that the sandy bed started to be covered with the fine sediment again from the downstream end to the upstream when the saltwater regularly intruded into the channel after the flood. This phenomenon might be caused by the estuarine residual circulation.