Post on 08-Oct-2020
Re-inventing Government Creek: Lessons from a
successful stream relocationKetchikan, AK
February 5, 2015
Michelle Havey, MS and Jon Houghton, PhDFunded by Alaska Dept. of Transportation
Contact: michelle.havey@hartcrowser.com
Project Background
Tongass Narrows
Ketchikan
Government Creek
Boulder Creek
Airport Creek
FAA: Need to expand RSA by 1000 ft on either end
Decision
• Re-route Government Creek into Boulder Creek channel near mouth
• Create new estuary
• Alternative option: very long culvert
Project Elements• Mainstem
• 3 Side Channels
• Expanded estuary
• North Tributary
Reference
Construction Statistics• Constructed 2006 – 2007
• Stripped and saved portion of overburden soil/vegetation
• Blasted and moved 380,000 cy of rock and till
• Maximum depth of cut ~80 feet
• Excavated to flat floodplain, in dry, without ‘technical’ oversight
Typical Cross Section
• 30 to 80-foot cut to floodplain (~150 foot wide)
• Then…
Main thalweg
Side channel
With Bio/Geomorphologist oversight (!):
With Bio/Geomorphologist oversight (!):
• Excavated main channel (~2,050 lineal feet ); 3 side channels (~800 lf)
• Installed habitat features (in dry)
– Stream bed “gravel”
– ~100 boulders (2 – 12 feet in diam.)
– ~ 50 trees (roots/limbs)
• Flow initiated in early August 2007
Monitoring Plan
• Estuary
– Saltmarsh area
– Eelgrass
– Fry rearing (coho)
• Schedule
– Pre- and Years 0, 1, 3, 5 (added Year 2, full monitoring)
• Stream
– Channel topography
– Physical habitat measures (retention of LWD)
– Bed grain size (pebble counts)
– Riparian vegetation
– Salmon spawning
– Fry rearing (coho)
Stream Success Criteria
Stream Success Criteria
• No barriers to upstream passage of juveniles at normal flows (tough!)
• Pink and chum spawning
• Instream structures retained (60% through Year 5)
• Coho rearing
• Native trees (4 spp.) by Year 5
• No excessive erosion on cut side slopes
• Side channel water quality ok for fry
Stream EvolutionYear 0
Stream EvolutionYear 3
Stream Evolution
Abundant Salmon Use• Pinks spawned within 2 weeks of flow initiation
• 2007 and 2008 cohorts returned in 2009 and 2010
• ~8,000 pink salmon observed in the constructed reaches!
• Also:
– Abundant juvenile coho
– Some Dolly Varden
– Trout fry
– Likely chum spawning
– One lonely Chinook in 2 of 3 years!
• Potential fish barrier
• Observed adult fish struggling to get upstream even during typical flows
Upper Cascade
• Pools/steps in bedrock
• Boulders
Upper Cascade Fix
Floodplain Erosion
Floodplain Erosion
• Routine overbank flow causes regular inundation and scouring of floodplain
• Recruits spawning gravel to channel
• Inhibited establishment of floodplain vegetation
Vegetation Establishment
• “Vegetation Islands” of armored sod from nearby forested uplands created as part of 2008 Adaptive Management
Vegetation Establishment
Stream Success Criteria
No barriers to upstream passage of juveniles at normal flows (tough!)
Pink and chum spawning
Instream structures retained (60% through Year 5)
Coho rearing
Native trees (4 spp.) by Year 5
No excessive erosion on cut side slopes
Side channel water quality ok for fry
Estuary Success Criteria
• Saltmarsh area requirements (Years 3 & 5) - % and sf
• No “excessive” channel or beach erosion
• Coho rearing
Estuary Design
Estuary Design• Created by
excavating & re-grading upland forest to encourage tidal inundation
• Bed rock encountered in excavation
• Saltmarsh vegetation salvaged during construction
Original tree/HWL
Saltmarsh vegetation
• Sod transplants doing well and spreading
• Distinct lack of saline inundation on upper portions of beach – tracking by line of alder dominance
Saltmarsh vegetation
• Year 4: more salt-tolerant sp.
• Year 6: met the 50% coverage criteria by saltmarsh species
Estuary Erosion
Looking downstreamLooking upstream
Estuary Erosion
• Significant intertidal erosion due to increased stream power
• Delta growth & braided channel
• Pilings not observed during construction!
Areas of Change:
• Eelgrass loss in delta
• Clam resources affected
• Low-tide channel erosion
• Delta formation
Estuary Step Work
• Part of Adaptive Management
• Potential bedrock ledge fish barrier
• Created pools/steps in bedrock ledge
After
Before
During
Estuary Success Criteria
Saltmarsh area requirements (Years 3 & 5) - % and sf
No “excessive” channel or beach erosion
Coho rearing
Conclusion• Rate of change, high in Year 1,
slowed in Years 2-6
• Successful salmon spawning and rearing habitat
• Appear to be meeting all fish-related criteria
• Vegetation in floodplain and saltmarsh met criteria
• Estuary erosion greater than expected, but stabilized
• Adaptive management can work!
Questions?