Abstract

Field surveys and remote sensing are used to monitor sediment grain-size characteristics and channel geometry on the lower Elwha River, Washington, USA. Data are collected biannually as a baseline against which the response of the river to the removal of two large hydroelectric dams, scheduled to begin in 2009, will be measured. Channel topography and sediment grain size are measured in representative reaches of the channel on the floodplain below the lower dam, and in a control reach above the upper dam. Restoration of a river to its natural state by the complete removal of dams of this size (32 and 64 m high) has never before been attempted. This system thus provides an opportunity to study the fluvial and coastal-watershed response to a large, regulated influx of sediment on a scale not previously possible. Present studies on the Elwha River generate necessary information prior to the beginning of dam removal, and also provide a unique opportunity to evaluate the predictive capability of sediment-transport and bed-evolution models. The parameters that this study measures have important implications for ecological and cultural effects of dam removal, affecting aquatic habitat, flood-hazard potential on the lower floodplain where the Lower Elwha Klallam Indian reservation is located, and evolution of the coastal sedimentary system.

Keywords: Fluvial Geomorphology, Dam Removal, Channel Pattern, Sediment Transport