SS3.21 Deconstructing Rivers: The Ecological, Geomorphic, and Social Consequences of Dam Removal
Date: Thursday, June 13, 2002
Time: 10:15:00 AM
Location: Colwood
 
BromleyJC, University of Nottingham / Oregon State University, Corvallis, USA, bromley@geography.nottingham.ac.uk
Grant, G, E, US Forest Service, Corvallis, USA, Gordon.Grant@orst.edu
Thorne, C, R, University of Nottingham, Nottingham, United Kingdom, 
 
THE GEOMORPHIC EVOLUTION OF THE LAKE MILLS RESERVOIR DELTA, ELWHA RIVER, WA: COMPLEX RESPONSE AND ITS IMPLICATIONS FOR SEDIMENT MANAGEMENT DURING DAM REMOVAL.
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A drawdown experiment conducted in the Lake Mills Reservoir indicates that the delta system exhibits a complex response, in which vertical adjustments occur in response to periods of falling baselevel, while lateral adjustments occur by mass wasting during periods of both falling and constant baselevel. Towards the delta front there is a clear decrease in bed elevation and increase in channel width. In the lower-middle delta, the clarity of this signal begins to decrease, reflecting both the decreased influence of the driving force (baselevel adjustment) and the increase in temporary sediment storage of sediment eroded from upstream. The rates of vertical and lateral adjustment exhibit an oscillatory response about the line of zero mean adjustment, similar to Hey’s (1979) conceptual model of channel evolution. Continued lateral channel adjustments during periods of constant baselevel appear to encourage deposition of sediment at the margins of the retreating reservoir. This may encourage recolonization, and therefore stabilization, by vegetation and thus a potential reduction in the volume of sediment released downstream.