Re-inventing Government Creek: Lessons from a successful ...€¦ · Estuary Design. Estuary Design •Created by excavating & re-grading upland forest to encourage tidal inundation

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: [email protected]

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?