In April 1994 a drawdown of Lake Mills, the reservoir behind Glines Canyon Dam on the Elwha River in Washington, was performed in order to gain an insight into how the sediment accumulated in the reservoir’s delta would respond to a dam decommissioning scenario. Analysis of the data collected reveals that the bulk of the morphological adjustment is concentrated in the finer sediments of the lower half of the delta, and that the delta channels exhibit a complex response that is primed by the drop in baselevel and driven by a relatively low discharge. A sediment budget for this channel evolution was developed.

In view of the spatially and temporally limited nature of the drawdown experiment, it is not possible to say with any degree of certainty the extent to which this pattern of channel evolution will be replicated under a full dam decommissioning scenario. In order to develop useful sediment management information for such an occurrence a series of Froude-scaled physical model experiments are proposed, in which a number of different dam removal and reservoir drawdown scenarios could be investigated under different discharge regimes. The results of a small sand box study are presented that provide a qualitative insight of how the Lake Mills system may respond.