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

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.

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

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

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

Longitudinal Profile and Pebble Counts

Pebble Counts

Channel Migration: Aerial Photos

Channel Migration

Channel Migration

HECRAS Model

Sediment Transport Analysis

GRAVEL BAR STORAGE

Floodplain connectivity

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

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

Questions?