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Natural Stream Channel Design (NSD) and in‐stream structures
Cross – VaneW – WeirJ – Hook
Root Wad / Log ‐ vane
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Restoring equilibrium with NSD techniques
• Leopold (1964) found that river form is associated with an integration of 8 factors:
1. slope
2. width
3. depth
4. velocity
• Together, these variables can be integrated into geomorphological relations for stable streams and rivers
• This is how the Rosgen ‘reference reach’ is established
5. discharge
6. boundary roughness
7. size of sediment transported
8. concentration of sediment
*See Vannote, ‘The River Continuum Concept’ for another related perspective
‘Soft’ structural stream ‐ enhancement
The Cross‐Vane, W‐Weir and J‐Hook Vane are Natural Stream Design structures that can be implemented to maintain or enhance river stability and function to facilitate multiple objectives
These structures have been successfully applied in natural channel design for:
river restoration
bank stabilization
grade control
irrigation diversions
fish habitat enhancement
bridge protection, and
recreational boating
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‘Soft’ structural stream ‐ enhancement
1) establish grade control
2) reduce streambank erosion
3) facilitate sediment transport
4) provide for irrigation diversion structures
5) enhance fish habitat
6) maintain width/depth ratio
7) improve recreational boating
8) maintain river stability
9) dissipate excess energy
10) withstand large floods
11) maintain channel capacity
12) be compatible with natural channel design
13) be visually acceptable to the public
To achieve these objectives, in‐channel structures have been developedand engineered in order to specifically address the following:
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Understanding the river – Collecting data
• Structures are often placed in rivers in an attempt to correct some of the adverse effects of channel adjustment due to instability
• Unfortunately, many structures are often installed to “patch a symptom” rather than achieve the stable channel form
• River engineering structures need to be incorporated with a clear understanding of the river variables that constitute the stable form– Understanding the “rules of the river” is crucial
– Otherwise, you can create more problems than you started with
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Importance of data collection
• Data from natural rivers indicate a negative power function relation between sinuosity and slope
• Thus when slope is decreased there is a corresponding increase in sinuosity through lateral migration following bank erosion
• Relations to determine the minimum size of rock for these structures are presented based on bankfull shear stress
Rosgen, 2006 ‐ Images: J.D. Kurz
Importance of data collectionBoundary shear stresses associated with high velocity gradients, can accelerate erosion
rates, and are shown in the velocity isovel constructed from vertical velocity profiles
C3 stream type is a slightly entrenched, meandering, riffle/pool, cobble-dominated channel with a well -developed floodplain
Riffle/pool sequence isgenerally 5 – 7 bankfullchannel widths
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In‐stream structures
Cross ‐ Vane• A grade control structure that:
– decreases near‐bank shear stress
– velocity, and
– stream power
but increases the energy in the center of the channel
• It does this by:– establishing grade control
– reducing bank erosion
– creating a stable width/depth ratio
– maintaining channel capacity
– maintaining sediment transport capacity
• Also popular for improving:– Stream habitat
– Kayak recreation
Rosgen, 2006 ‐ Images: J.D. Kurz
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Step‐pools using cross‐vanes
• The Cross‐Vane is used to maintain base level in:– both riffle/pool channels
– rapids‐dominated stream types
– step‐pool channels
• Used for:– grade control
– maintaining new width/depth ratio
– entrenchment ratio
– reducing bank erosion
– dissipating energy
– improving fish habitat
Rosgen, 2006 ‐ Images: J.D. Kurz
W ‐Weir• Installed as if the W I looking downstream
• W‐Weir is similar to a Cross‐Vane in that both sides are vanes directed from the bankfull bank upstream toward the bed with similar departure angles
Structure createstwo thalwegs
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W ‐Weir• W – weirs are constructed on very wide rivers and/or where two center
pier bridge designs require protection
• Habitat for trout is enhanced by maximizing usable holding, feeding and spawning areas
• Fish hold in the multiple feeding lanes created by the two thalweg locations and pools
• Various age classes of trout also hold in the deep glide created upstream of the structure and against both banks due to the increased depth and reduced velocity of flows in the near‐bank region
• Spawning habitat is created in the tail‐out of the pools due to upwelling currents and a sorting of gravel bed material sizes preferred by trout
J – Hook Vane• Directed upstream, this structure can
include:– Boulders
– Logs, and
– Root wads
and is located on outside of stream bends
• Designed to reduce:– bank erosion by reducing near‐bank slope
– velocity
– velocity gradient
– stream power, and
– shear stress
• The vane portion of the structure occupies 1/3 of the bankfull width of the channel, while the “hook” occupies the center 1/3
Rosgen, 2006 ‐ Images: J.D. Kurz
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Root wad / log –vane / J – hook
• A combination of structures that provides streambank stabilization and fish habitat
• The placement of the ‘root wad’ and footer log simulates an under‐cut bank
Rosgen, 2006 ‐ Images: J.D. Kurz
NSD Structure uses
• The Cross‐Vane, W‐Weir and J‐Hook Vane are structures that can be implemented to maintain or enhance river stability and function to facilitate multiple objectives
• These structures have been successfully applied in natural channel design for river restoration, bank stabilization, grade control, irrigation diversions, fish habitat enhancement, bridge protection, and recreational boating
• Continued monitoring will provide the information necessary to improve the designs to further their application to meet the ever‐increasing demand for environmentally “softer” structures that meet multiple objectives
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