Steelhead Haven Landslide Steelhead Haven Landslide Fine Sediment Reduction Fine Sediment Reduction

Project Project

Tracy Drury, PEAnchor Environmental L.L.C.

Pat StevensonStillaguamish Tribe of Indians

Stillaguamish Tribe’s InterestsStillaguamish Tribe’s Interests

Chinook Populations at 8% of historic levels

Fine sediments inputs was determined to be a major contributing factor

Success would improve habitat conditions for more than 30 miles downstream

Steelhead Haven Landslide 2004Steelhead Haven Landslide 2004

Historical PerspectiveHistorical Perspective

19651965 20002000

Then came 1967…Then came 1967…

Project PlanningProject Planning

Prioritized in the Chinook recovery plans, 1990, 2000, 2005

Began community involvement / public outreach, 1995

Evaluated in the Corps Ecosystem Restoration Plan, 2000

Conceptual Designs Developed, 2001

Funding for design and construction: Salmon Recovery Funding Board (500K) and Centennial Clean Water (500K), 2005

Project DesignProject Design

Design conducted, 2005-06Design conducted, 2005-06

ObjectivesObjectives Maximize sediment storageMaximize sediment storage Promote long-term stabilization of the slidePromote long-term stabilization of the slide Improve in-stream habitat conditionsImprove in-stream habitat conditions

ConstraintsConstraints No increase in flood impact to the local communityNo increase in flood impact to the local community

Preliminary Design ConceptPreliminary Design Concept

Slide Failure: January 2006Slide Failure: January 2006

BackwaterBackwater at low flowat low flow

Management ConcernsManagement Concerns

Management ActionsManagement Actions

Opening a channelOpening a channel

Channel BeginningsChannel Beginnings

January 29January 29thth 2006 2006

Flow through the treesFlow through the trees

Where the river wants to goWhere the river wants to go

Channel we clearedChannel we cleared

Former Former ChannelChannelBankBank

Pre-slidePre-slideHead scarpHead scarpLocation Location

730730FeetFeet

Post Slide Post Slide ChannelChannel

Redesign ConditionsRedesign Conditions

Creek Draining the SlideCreek Draining the Slide

Creek Mixing with RiverCreek Mixing with River

Project DesignProject Design

Design conducted, 2005-06

Objectives Maximize sediment storage Promote long-term stabilization of the slide Improve in-stream habitat conditions

Constraints No increase in flood impact to the local community

River 2D Hydraulic Model Output - DepthRiver 2D Hydraulic Model Output - Depth

River 2D Hydraulic Model Output - VelocityRiver 2D Hydraulic Model Output - Velocity

Expected Channel MigrationExpected Channel Migration

Expected Head cutExpected Head cut

Expected ChangeExpected ChangeLog Cribwall PlacementLog Cribwall Placement

Temporary Bridge Temporary Bridge

Isolating the River From the Construction Isolating the River From the Construction

Log Cribwall 1300 feet long, 25 feet high Log Cribwall 1300 feet long, 25 feet high

Ballast Blocks Approximately Every 50 Feet Ballast Blocks Approximately Every 50 Feet

Backfilled With Woody Debris Backfilled With Woody Debris

What the River Will See What the River Will See

Approximately 20 Acre-feet of StorageApproximately 20 Acre-feet of Storage

As-BuiltAs-BuiltConditionsConditions

First Flood EventFirst Flood Event

Channel Migrated Toward the StructureChannel Migrated Toward the Structure

Migration Progressing Downstream Migration Progressing Downstream

Take Home MessagesTake Home Messages

Landslide failure forced redesign to be more highly engineered placement

Constructability was a major decision making factor

The structure was designed to deform and settle as the river undercuts it’s face

Thorough analysis and communications prior to the failure facilitated permit acquisition after the failure

Steelhead Haven Landslide Steelhead Haven Landslide Fine Sediment Reduction Fine Sediment Reduction

Project Project

Tracy Drury, PEAnchor Environmental L.L.C.

Pat StevensonStillaguamish Tribe of Indians