An assessment of stream bank stabilization techniques using upstream and downstream pointed vane structures. - Alexandre Lai , Alyeska Pipeline (co-authors: Horacio Toniolo/UAF)

ABSTRACT

Various instream type structures have been used historically to stabilize stream banks, protect infrastructure and / or channel restoration. These structures typically protrude into the active floodplain or stream channel. They are known under various names such as groynes, spur dikes, cross vanes, j-hooks, flow retard or redirectional vanes, bendway weirs, etc. This study evaluated two bank stabilization techniques located along the Dalton Highway corridor:

1. At Hess Creek near Dalton Highway milepost (DHMP) 25, downstream pointed re-directional vanes where used to re-align an outside meander bend with the Trans-Alaska Pipeline (TAPS) bridge opening.
2. On the Sagavanirktok River near DHMP 414, upstream pointed structures similar to bendway weirs where installed on a side channel to protect the highway from an eroding bank due to lateral migration of a meander bend.

The two sites have very different morphologies, at Hess Creek the stream is a single channel located in an interior Alaska boreal forest environment with intermittent permafrost. At the Sagavanirktok River the channel is braided with continuous permafrost and in an arctic tundra environment.

Preliminary results show that upstream pointed structures have deeper scour holes due to its sharp angle in relation to incoming flow and experience higher shear stresses. The downstream pointed redirective vanes have lower shear stresses and shallower scour holes. Both designs have thus far met their intended goals of protecting the eroding bank. In addition they both differ from traditional engineering rock revetments by providing flow diversity such as eddy currents along the meander bend. The eddies generated downstream of the vanes are a result of flow separation and they enhance aquatic habitat by providing resting and feeding areas for migrating fish.

The choice of which technique to use depends on factors such as economics, channel morphology, available construction material, desired function and purpose of the design.

Topic: Alaska Hydrology