Spawning Gravel

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Spawning Gravel

• Placement, nourishment, stabilization, and
  cleaning of spawning gravel
• Kozmo Ken Bates Kozmo_at_AquaKoz.com

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What makes spawning habitat?

• Size distribution of substrate
• Permeability, compaction
• Hydraulics
• Depth, velocity, intergravel flow, upwell
• Water quality dissolved oxygen
• Proximity to cover
• Self-sustaining

Upwell figure
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Impacts to Spawning Habitat

• Loss of substrate
• Hydraulics of channel incision, straightening,
  armoring
• Scour from floods or splash dams
• Removal or blockage of wood
• Recruitment blocked
• Blockage at dams
• Loss of source by bank armoring
• Intrusion of fines
• Single event or chronic
• Instability during spawning

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Spawning Gravel Other Impacts

• Loss of upwell flow when gravel bars lacking
• Loss of invertebrate productivity in compacted
  bed
• ll

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Spawning Gravel Restoration Methods

• Direct placement - spawning pads
• Nourishment
• Trapping
• Stabilization
• Side channels (other technique)
• Cleaning

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Geomorphic Context
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Spawning Gravel Placement

• Direct placement - Pads
• Appropriate where gravel sources are lost
• Temporary fix unless hydraulics are appropriate.
  Tailout of drop structure or constriction with
  specific headloss
• Spring channel enhancement

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Spawning Gravel Pads
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Spawning Pads - Risks

• Displaces and affects other habitats
• Attractive nuisance
• Gravel is not hydraulically sorted or place and
  therefore unstable for spawning
• Gravel is not persistent in high energy areas
• Gravel may not be persistent over hard bed
• Potential low depth passage barrier

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Spawning Gravel Nourishment

• Create gravel bluff or bar
• High flows distribute material naturally
• Applies downstream of gravel traps (dams)
• Restocking of bar or bluff is based on monitoring
  of bar (for quantity) or gravel downstream (for
  habitat)
• Can be appropriate above high energy channels to
  create pocket gravel

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Washington Spawning Nourishment Sites

• Mitigation below dams
• Cedar River
• Green River
• Cowlitz River
• Spokane River
• Green River

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Cedar River Gravel Nourishment

• Downstream of Landsburg Dam
• About 1,000 cy to placed 2001-2006 except 2002
• Material specified generally 5 to 50 mm
• Placed as gravel bar to be washed downstream

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Cedar River gravel nourishment plan
Placement berm
2 Downstream cross-sections
1 Control cross-section
2002 Channel work
City of Renton, Golder Associates drawing
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City of Renton, Golder Associates photo
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Cedar River Gravel Monitoring

• Care of fish
• Timing
• Snorkel surveys
• Erosion and sediment control
• Turbidity monitoring
• Gravel supplementation
• Sieve analysis of placed material
• Channel cross-sections at site and control
• Pebble counts at transects downstream and control

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Results Cross-Section 3 2001-2006 (my trend
lines by eye)
Spawning gravel 10 - 60 mm
City of Renton, Golder Associates data
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Results Cross-Section 4 2001-2006 (my trend lines)
Spawning gravel 10 - 60 mm
City of Renton, Golder Associates data
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Keswick Dam, Sacramento R Feeder bluff
supplementation 100,000 cy gravel added at 8 sites
Resulting Chinook redd
Feeder bluff
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Green River Gravel Nourishment

• Corps 1125 project
• Now part of Howard Hanson Dam Bi-op for Chinook
  and bull trout
• Objectives
• Increase spawning for coho, Chinook, steelhead
• Reconnect side channels and floodplain
• Reverse bed armoring
• Restore natural gravel transport

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Other Project Parts

• Gravel Nourishment
• Loose wood
• Log jams

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Debris jams
Nourishment bars
Nourishment bars
USACE photo
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Monitoring

• Intensive monitoring for five years
• Background for management of 50-year project

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Gravel Monitoring Questions

• Are gravel berms effectively providing spawning
  gravels each year?
• What is the rate of gravel transport through the
  reach? How does gravel size affect transport?
• How is substrate composition changing downstream?
• What is the effect of gravel nourishment on
  Chinook and steelhead spawning?
• Log jam and loose wood monitoring also

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Geomorphology Monitoring

• Changes in channel morphology?
• Change in water surface elevation?
• Channel migration?
• Localized storage of spawning gravel?
• Signs of bank erosion?
• Due to any or all three activities.

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Spawning Monitoring Activities

• Low flow / spring survey of gravel berms
• Post high flow / visual inspection of gravel
  berms
• Photo points
• Survey cross-sections
• Pebble counts
• Gravel patch mapping / aerial photo analysis
• Side channel water levels (G)
• Fall spawner survey
• Habitat mapping (H)
• Hydrology

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• See recommendations for future monitoring

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USACE photo
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Photopoint 17 Looking downstream at ELJ2
Sept 2003
July, 2005
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Before after shots
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USACE photo
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USACE contact
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Risks

• Fish spawning on fresh gravel Green River
• Material transported at low events
• Constriction of channel changes hydraulics locally

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Spawning Gravel Trapping

• Outlet cr

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Cedar Cr Fish First project
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Cedar Cr Fish First project
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Risks

• Installation of trapping structures
• Backwater effects

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Spawning Gravel Cleaning

• Cleaning of in-place channel bed
• Mechanical
• Hydraulic
• Temporary solution
• Use only if one-time sediment effect or source is
  remedied
• High cost
• Not a current practice

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Spring channels
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Spawning Gravel CleaningGravel Gertie
Jets clean to 12 deep Fines decreased 3 to
78 Siltation partially confined in hoods
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Spawning Gravel CleaningOther Cleaning Mechanisms

• Maybe drop this slide

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Spawning Gravel CleaningEffects

• High level of disturbance
• Flattens and lowers streambed
• Temporary attractive nuisance of unstable bed
• Impact is limited with smaller equipment
• Removes invertebrates
• Re-colonized within weeks
• Water quality impacts moves some of the sediment
  downstream

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Spawning GravelComplementary Techniques

• Restore channel profile, floodplain connectivity
• Remedy sources of fines
• Add roughness to trap gravel
• Debris, boulders, drop structures
• Add structure to distribute and sort gravel
• Debris, boulders, drop structures

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Spawning Gravel RestorationUncertainties

• Uncertainties are high for placement
• Depends on flow events
• Uncertainty low for supplementation
• Monitoring required

K Bates
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Spawning GravelMonitoring
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Last thoughts

• To be sustainable, spawning gravel is the right
  combination of
• Gravel source
• Hydrology
• Hydraulics
• Its tough to improve on natural spawning
  habitats.

Without all 3, its not spawning habitat.