What is channel migration?
River channels can move, or migrate, laterally across their floodplains. Channel migration can occur gradually, as a river erodes one bank and deposits sediment along the other. Channel migration also can occur as an abrupt shift of the channel to a new location, called an avulsion, which may happen during a single flood event. There are several areas in King County with migrating river systems that represent hazards to permanent structures. The highest rates of channel migration occur in zones of rapid sediment deposition, e.g., where steep rivers flow out of foothills onto flatter floodplains. Channel migration represents a different type of flood hazard than getting inundated by overbank flow, and can endanger properties located outside of the regulatory floodplain. Channel migration can endanger properties outside of the floodplain. The erosion caused by channel migration can undermine houses, roads, and infrastructure, wash away property, and threaten lives. It may be the least re
