SESSION D:

Title: Incorporating Stream Morphology Into Barrier Removal Design

Author: Matt Bernier, P.E.
Kleinschmidt Associates, P.O. Box 576, Pittsfield, ME 04967; 207/487-3328; matt.bernier@kleinschmidtUSA.com

Abstract:

Some barriers to fish passage, including dams and culverts, have been removed in New England with little restoration activity beyond the physical removal of the fish passage barrier itself. The expectation is that fluvial geomorphic processes, like streamflow and sediment transport, will restore streams to natural and sustainable conditions once the barrier is removed. Many of these projects also rely upon natural revegetation of floodplains and streambanks. The reliance on natural processes is largely driven by concerns about the costs of implementation and long-term maintenance for barrier removal projects.

The author will present information about how fish passage barriers, such as culverts and dams, alter streams in ways that may challenge natural restorative processes, especially in the short term. Scour pools downstream of barriers, for example, may create unsustainable streambed slopes once a barrier is removed, which can result in migrating headcuts and bed failure. A barrier removal can also release previously impounded sediments that can overwhelm the sediment transport ability of a stream, and embed downstream habitat. Dewatered stream reaches are also vulnerable to colonization by exotic/invasive plant species.

Using real projects as examples, the author will demonstrate how stream morphology can be incorporated into restoration design, and how to determine the appropriate level of restoration required for each project, including streambed rebuilding and planting plans. The presentation will include brief introductions to design and assessment tools such as historical research, fluvial geomorphology (hydrology, sediment transport), regional stream-geometry equations, and reference reaches.