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Redefining the dam removal paradigm in formerly glaciated forested headwater systems

1024 681 Stroud Water Research Center

Daniels, M.D., D. Burchsted, J. MacBroom, L. Wildman, S. Harold, M. Carabetta, P. Woodworth, and G. Boardman. 2010. Pages 1750–1758 in R.N. Palmer (editor). Proceedings of the World Environmental and Water Resources Congress 2010, Providence, Rhode Island.

doi: 10.1061/41114(371)184

Abstract

The conventional paradigm of dam removal includes an expectation of substantial sediment releases from impoundment storage accompanied by problematic downstream flushing transport and deposition. This expectation is largely based on the River Continuum Concept (RCC) model of streams. However, the pre-dam longitudinal profile of many headwater streams is not that of the stereotypical RCC continuously steep gradient, but rather a more stepped profile including high gradient transport-regime reaches interrupted by lower gradient depositional reaches. In fact, headwater stream systems are frequently punctuated by low gradient, wetland or wet meadow reaches produced by a variety of geologic controls. Modern impoundments now are emplaced within this discontinuous, stepped, longitudinal gradient of erosion-resistant transport reaches and low gradient depositional reaches, and the risks associated with sediment releases from dam removals are minimized by the downstream presence of depositional reaches capable of receiving and storing sediment released from upstream. Furthermore, it is quite likely that many headwater dams were constructed at pre-existing depositional reaches, creating the likely scenario that the impoundment sediments would be largely stable upon dam removal. In regions where these conditions are present, significant costs and delays associated with unnecessary sediment stabilization and or sediment removal are preventing the timely restoration of our headwater systems.

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