Invertebrate dynamics in the downstream of a dam after sediment supply — ASN Events

Invertebrate dynamics in the downstream of a dam after sediment supply (#233)

Norio Tanaka 1 , Ryosuke Sakata 1
  1. Saitama University, Saitama, SAITAMA, Japan

Sediment replenishment has been recently conducted for improving river environment downstream of a dam. However, there are still many unknown as for the amount and appropriate sediment size for the replenishment. Especially, the effects on stream biota is still unknown in relation to the sediment supply. The objective of this study is to clarify the invertebrate dynamics after sediment supply in relation to the hydrodynamics at the site. For the objective, this study selected three types of benthic insects considering their motion, creeping type/swimming type or habitat characteristics . For flume experiment with invertebrates, creeping type invertebrate is selected, and the critical velocity for walking is investigated. Washout condition of invertebrates was also tested in situ at downstream of the Futase Dam. Using the limit condition of walking and washout, the dynamics of invertebrates that have different strategy in each has been discussed. The change of sediment size, including the deposited sediment size just behind rocks or boulders were monitored and the relationship was analyzed. The critical velocity for the initiation of sediment and habitat height related to the sediment transport mode (bed load/suspended load) is also assumed an important factor for the change of the invertebrate composition.

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