Dam removal has recently emerged as a growing trend in river rehabilitation in the
United States. The rate of dam removal has been increasing rapidly since 2000, but is
doing so with large gaps in our understanding of how the fluvial system will respond
to this disturbance. Most of the structures removed to date have been relatively small
and, in the vast majority of cases, have not received any pre- or post-removal
monitoring. Very few large structures have been removed but, when such removals
occur or are proposed, they tend to attract more monitoring activity because of the
generally larger volumes of water and sediment involved. It is thus important to
understand the form-process-response interactions that occur during the removal of
large dams and the extent to which these may be applicable to other removals of
The proposed removal of the Glines Canyon Dam from the Elwha River in
Washington, USA provides such an opportunity. The 67-m high dam is due to be
incrementally removed in 2011 but its reservoir, Lake Mills, contains 80 years-worth
of uncontaminated sediment that has the potential to adversely impact the aquatic and
human environment once released into the channel downstream from the dam. In
order to better understand the dynamics that control how sediment might be
transported into the downstream channel, a series of scaled physical model
experiments was performed in which the principle variable investigated was the
magnitude of the drop in reservoir water surface elevation.
Four main findings emerged from the research. First, the hypothesised relationship
between increasing magnitudes of baselevel drop and increasing delta erosion
volumes is only weakly developed. Furthermore, the small increases in additional
erosion volume for very large increases in magnitude of drop suggest that there may
be an upper limit beyond which the volume of sediment eroded does not increase
substantially, irrespective of the magnitude of drop. The reasons for this are explored.
Department of the Interior, US Bureau of Reclamation
Sediment Processes Associated with the Removal of the Glines Canyon Dam.
St. Anthony Falls Laboratory.
Retrieved from the University of Minnesota Digital Conservancy,
Content distributed via the University of Minnesota's Digital Conservancy may be subject to additional license and use restrictions applied by the depositor.