re-inventing government creek -- lessons from a successful...
TRANSCRIPT
-- Lessons from a successful
salmon stream and estuary relocation on Gravina Island
Jon Houghton, Ph.D. and Derek Ormerod, M.S., P.E. -
Pentec Environmental/Hart Crowser, Inc.
D. Shane Cherry, M.S. - Cherry Creek Environmental
Lance Mearig, P.E. - USKH Corporation
February 2, 2010
contact: [email protected]
Re-inventing Government Creek
FAA: Need to expand RSA by 1000 ft on either end
Alternative: long culvert
Project Background
Airport Cr.
Government Cr.
Boulder Cr.
Tongass Narrows
Adaptive Management by IDT
- Interdisciplinary Team (IDT=ADOT&PF, ADF&G, NMFS, FWS, USACOEand consultant team)
- Reviewed and Approved:> Approach
> Design> Monitoring Plan
- Review Monitoring Reports
- Review and approve AM actions
Decision:
Re-route Government Cr. into Boulder Cr. channel near mouth; and create new estuary
(alternative option: very long culvert)
Project Elements
Mainstem; 3 Side Channels; Expanded Estuary; North Tributary
Constructed 2006 – 2007
Stripped and saved portion of overburden soil/vegetation
Blasted, ripped, and moved 380,000 cy of rock and till
Maximum depth of cut approximately 80 feet
Excavated to flat flood plain, in dry, w/o „technical‟ oversight
Statistics:
Typical cross section
30 to 80-foot cut to flood plain(~150 foot wide)
Then…
Excavated main channel and 3 side channels
Built ~2,050 lineal feet of new channel, plus ~800 feet of side channels
Installed habitat features (in dry)
- Stream bed “gravel”
- Approx. 100 boulders 2 – 12 ft in diam.
- Approx. 50 trees w. roots/limbs
Flow initiated August 2007
With Bio-/Geomorpho-logist oversight (!):
contact: [email protected]
Monitoring PlanSchedule Pre- and Years 0, 1, 3, 5
In Stream - Channel topography Standard habitat measures (retention of LWD) Bed grain size (pebble counts) Riparian vegetation Salmon spawning Fry rearing (coho)
In Estuary Saltmarsh area Eelgrass Fry rearing (coho)
Stream Evolution
Spawning Gravel Original bed material did not meet spec
Too much sand and not enough gravel – washed away
Good gravel recruitment from eroding floodplain and glacial till
Have far exceeded performance goal (1,200 sf) each year, and continues to stabilize and expand
Abundant Salmon Use
Pinks spawned within 2 wks of flow initiation
2009 return of that cohort
3000+ Pink salmon observed in the constructed reaches!
Also, abundant juv coho, some DV, trout fry, likely chum spawning, and one lonely female Chinook!
Upper Cascade Fix
Potential cascade fish barrier – observed adult fish struggling to get upstream even during typical flows
With AMT/IDT ok, created pools/steps in bedrock and added boulders to break up flow
Estuary Design New estuary created by excavating and re-grading upland forest to encourage tidal inundation
Bed rock encountered in excavation
Salt-marsh vegetation salvaged during construction
Original tree/HWL
Salt-marsh vegetation
Sod transplants doing well and spreading
Year 2: first observed seedlings
Distinct lack of saline inundation on upper portions of beach – tracking by line of alder dominance
Estuary Erosion
Significant intertidal erosion
due to increased stream power
Delta growth and braided channel
Pilings not observed during construction!
Estuary Evolution
Areas of Change:
Low-tide channel erosion
Delta formation
Eelgrass loss in delta
Clam resources affected
Salt-marsh vegetation mixed with riparian vegetation
Estuary Step Work
Part of Adaptive Management Work
Potential bedrock ledge fish barrier
Created pools/steps in bedrock ledge
Before
During
After
Floodplain Erosion
Routine overbank flow causes regular inundation and scouring of floodplain
Recruits spawning gravel to channel
Has created additional side channels and pools that isolate fish as water recedes
Inhibits establishment of floodplain vegetation
Vegetation Establishment
Overbank flow scouring floodplain has allowed minimal natural recruitment of veg
“Vegetation Islands” of armored sod from nearby forested uplands created as part of
2008 Adaptive Management
Side Channels Created to provide juvenile coho rearing habitat
Have had concerns with in-flow rates and sediment deposition clogging lower side channel
Varying levels of effectiveness based on amount of flow
Do support juvenile coho
North Tributary Created to provide juvenile coho rearing habitat
Varying levels of habitat quality based on amount of flow
Very dense pink spawning in 2009
Success Criteria
Stream Channel No barriers to upstream passage of juv at normal flows (tough!) Pink and chum shall spawn Instream structures shall remain (60% thru Year 5) Coho shall rear Native trees (2 spp.) by Year 3 No excessive erosion on cut side slopes Side channel water quality ok for fry
Estuary Saltmarsh area (Year 3 and 5) No “excessive” channel or beach erosion Coho shall rear
Conclusions Rate of change, high in Year 1, has slowed in Year 2
Successful salmon spawning and rearing habitat
Appear to be meeting all fish-related criteria
Vegetation of flood plain uncertain
Estuary erosion still a concern, but stabilizing
Adaptive management can work!
