1. Snohomish County Surface Water Management R2 Resource Consultants
Restoration Assessments in Large Rivers: North Fork Stillaguamish river
Snohomish County Surface Water Management
R2 Resource Consultants

2. background Established Project Management/Technical Leads
SWM - Bob Aldrich
R2 – Paul DeVries
Similar Assessments Completed Previously:
Skykomish River – Braided Reach
Upper Sauk River
Lower Sauk River
Lower Skykomish River
South Fork Stillaguamish River
Stillaguamish River
Yakima River Wapato Reach (R2)
Some County funded, FCAAP program funded one, otherwise match for SRFB funded assessments came from County.

3. Basic Principles of approach
Scale becomes important in rivers. Need to identify/ quantify physical processes at reach scale before implementing projects at site scale
Simplicity and repeatability are key
Process-based analysis identifies characteristic large scale controls of slope & grain size, vertical and lateral stability, and hydrologic/hydraulic connectivity with floodplain
Recovery Plan Drives Target Species/Lifestage Needs
Use Assessment Results to Match Project Type to Need and Process

4. Goals and Objectives
Evaluate all non-tidal sections of major river channels in County using similar approach
Identify hydraulic/sediment transport processes, depositional patterns at reach scale
Identify most geomorphically active/ inactive segments in reach
Match project type with reach scale channel conditions as they affect the site in general

5. Framework Key Data Analyses Key Results Product Remaining Steps
Geomorphic/Hydraulic Assessment
Process Controls Aquatic/Riparian Habitat
Level of Activity/Inactivity Controls Project Performance/Success
Framework
HEC-RAS Model
LiDAR Topography
Aerial Photography
Grain Size Distribution
Hydrology
Key Data
Longitudinal Profiles:
Bed/Flood Elevation
Gradient
Grain Size
Hydraulic Geometry
Stability - Vertical:
HEC-RAS Model
50 Year Sediment Transport Budget
Floodplain Connectivity:
HEC-RAS Model
LiDAR DEM
GIS Mapping
Stability - Lateral:
GIS Mapping/Analysis
Channel Migration Rates
Analyses
Spatial/Temporal Variation:
Level and Nature of Geomorphic Activity/inactivity
Floodplain Connectivity, Frequency
Consistency Across Processes/Analyses
GIS Visualization
Key Results
Identify Sites, Projects in Reach (In)Compatible With Results:
Instream Habitat (Spawning, Rearing, Adult)
Side/Floodplain Channel Connectivity
Floodplain Building/Channel Aspect Ratio Modification
Riparian Restoration
Bank Protection
Product
Remaining Steps
Landownership/Infrastructure/Public Feasibility → Funding → Design → Permitting → Construction → Monitoring

6. Longitudinal Profile and Pebble Counts

7. Pebble Counts

8. Channel Migration: Aerial Photos

9. Channel Migration

10. Channel Migration

11. HECRAS Model

12. Sediment Transport Analysis

13. GRAVEL BAR STORAGE

14. Floodplain connectivity

15. Synthesis of Results
Use to identify analysis segments with higher and lower risks of:
Aggradation
Gravel bar disturbance after large flood
Channel migration/avulsion
Correlate with habitat and fish data
Can explain/describe reach scale processes to stakeholders, community
Guide future planning/actions
Fish habitat structures
Side channel/off channel habitat reconnection
Infrastructure/floodplain development concerns

16. Assessment approach was developed with intent to lead directly to projects
Identify Project Types at Locations That Are Compatible With:
Flooding & Geomorphic Activity Levels
Instream Habitat Projects Function Longer Where Activity is Lower
Side- & Off-Channel Habitat Connectivity More Likely Where Aggradation/Migration Activity is Higher, Flood-Engagement More Frequent
Projects not Advised Where Degradation Potential is High
Floodplain Connectivity, Flooding/Avulsion Risk Lower on Private Property
Reach Scale Changes in Slope/Confinement
Instream Habitat Projects Not Advised in Vicinity of Slope Break
Spawning Habitat Projects Less Fruitful in Confined Reaches
Reach Scale Patterns in Grain Size Linked to Spawning Habitat Restoration Potential

17. Questions?