Flow Structures

The basic premise behind in-channel stream management structures is that when water encounters a barrier to flow, it will cross that obstacle in a direction perpendicular to the orientation of the structure. The effectiveness of these structures lies in their ability to direct flow through and over their rock walls. Water is directed away from the bank to prevent erosion. Simultaneously, this concentration of flow carves a deeper channel in the middle of the stream. Flow "waterfalling" over the rock surface serves to deepen and elongate the scour pool. Dave Rosgen, the pioneer in this field, investigates the dynamics of stream flow in his paper on stream stabilization and river restoration, which you can view at this site. Here, the three stream management structures implimented in Seven Mile Creek are illustrated and explained.*

Cross Vanes

A cross vane is made up of a set of upstream angled lines of boulders, connected by a section of smaller rocks upstream. While water usually covers the shorter section during normal flows, the taller sections deflect flow away from the banks of the stream. Flow is diverted over the rock walls and concentrated down the center of the channel. The scouring associated with high flow velocities in the center of the channel and the "waterfalling" over the structure itself creates a deep, elongated pool.

J-Hook Vane

A J-hook vane is an upstream pointing line of rocks that originates at one bank and terminates somewhere in the middle of the stream. The most upstream portion of the structure bends back on itself, like a "J," curving into the middle of the channel. This bent portion serves to concentrate flow and scour out a pool while the length closer to the shore deflects flow away from the bank.

Where a cross vane incorporates two structures on opposite banks cooperating to control flow, J-hook vanes are often constructed in series on the same bank. This technique was implemented in the SMC rehabilitation project to protect a bridge embankment from being eroded.

 

Willows

Willows are planted on the creek bank to reduce erosion and provide cover for fish. Their root structures hold together the soil of the stream bank, increasing its structural integrity. They grow very quickly and in dense patches, which hang over the water and offer shady cover.

*Diagrams from Rosgen, D.L. The Cross-Vane, W-Weir, and J-Hook Vane, Structures...Their Description, Design and Application for Stream Stabilization and River Restoration. http://www.wildlandhydrology.com/assets/cross-vane.pdf

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