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Spawning Gravel Placement, nourishment, stabilization, and cleaning of spawning gravel Kozmo Ken Bates –

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Presentation on theme: "Spawning Gravel Placement, nourishment, stabilization, and cleaning of spawning gravel Kozmo Ken Bates –"— Presentation transcript:

1 Spawning Gravel Placement, nourishment, stabilization, and cleaning of spawning gravel Kozmo Ken Bates –

2 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


4 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

5 Spawning Gravel – Other Impacts Loss of upwell flow when gravel bars lacking Loss of invertebrate productivity in compacted bed ll

6 Spawning Gravel Restoration Methods Direct placement - spawning pads Nourishment Trapping Stabilization Side channels (other technique) Cleaning

7 Geomorphic Context

8 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

9 Spawning Gravel Pads

10 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

11 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

12 Washington Spawning Nourishment Sites Mitigation below dams –Cedar River –Green River –Cowlitz River –Spokane River –Green River

13 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

14 City of Renton, Golder Associates drawing Placement berm2 Downstream cross-sections 1 Control cross-section 2002 Channel work Cedar River gravel nourishment plan

15 City of Renton, Golder Associates photo


17 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

18 Results Cross-Section 3; 2001-2006 (my trend lines by eye) “Spawning gravel” 10 - 60 mm City of Renton, Golder Associates data

19 Results Cross-Section 4 2001-2006 (my trend lines) “Spawning gravel” 10 - 60 mm City of Renton, Golder Associates data

20 Keswick Dam, Sacramento R Feeder bluff supplementation 100,000 cy gravel added at 8 sites Feeder bluff Resulting Chinook redd

21 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

22 Other Project Parts Gravel Nourishment Loose wood Log jams

23 USACE photo Nourishment bars Debris jams Nourishment bars

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

25 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

26 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.

27 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

28 See recommendations for future monitoring


30 USACE photo



33 Sept 2003 July, 2005 Photopoint 17 Looking downstream at ELJ2


35 Before after shots

36 USACE photo

37 USACE contact

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

39 Spawning Gravel Trapping Outlet cr

40 Cedar Cr Fish First project


42 Risks Installation of trapping structures Backwater effects

43 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

44 Spring channels

45 Spawning Gravel Cleaning “Gravel Gertie” Jets clean to 12” deep Fines decreased 3 to 78% Siltation partially confined in hoods

46 Spawning Gravel Cleaning Other Cleaning Mechanisms Maybe drop this slide

47 Spawning Gravel Cleaning Effects 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

48 Spawning Gravel Complementary 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

49 Spawning Gravel Restoration Uncertainties Uncertainties are high for placement –Depends on flow events Uncertainty low for supplementation –Monitoring required K Bates

50 Spawning Gravel Monitoring

51 Last thoughts To be sustainable, spawning gravel is the right combination of 1.Gravel source 2.Hydrology 3.Hydraulics It’s tough to improve on natural spawning habitats. Without all 3, it’s not spawning habitat.

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