Lower Pilchuck River Assessment December 31, 2018 Prepared for Snohomish County Surface Water Management Lower Pilchuck River Assessment Contact Information Document Information Cardno Prepared for Snohomish County Surface Water 801 Second Avenue Management Division Suite 1150 3000 Rockefeller Avenue Seattle, WA, 98104, USA Everett, WA 98201 Telephone: +1.206.269.0104 www.cardno.com Project Name Lower Pilchuck River Assessment Date December 2018, Final December 2018, Final Cardno Document Information i Lower Pilchuck River Assessment This Page Intentionally Left Blank ii Document Information Cardno December 2018, Final Lower Pilchuck River Assessment Table of Contents 1 Background and Purpose .............................................................................................. 1-1 2 Overview .......................................................................................................................... 2-1 2.1 Study Area ........................................................................................................................ 2-1 2.2 Geologic Setting ............................................................................................................... 2-2 2.3 Prior Work ......................................................................................................................... 2-2 2.4 Gravel Mining ................................................................................................................... 2-3 2.5 Fish Habitat ...................................................................................................................... 2-4 3 Restoration Planning and Prioritization ........................................................................ 3-1 3.1 Approach .......................................................................................................................... 3-1 3.2 Reach-By-Reach Conditions and Potential Actions ......................................................... 3-2 3.2.2 Reach 8 ............................................................................................................. 3-3 3.2.3 Reach 7 ............................................................................................................. 3-5 3.2.4 Reach 6 ............................................................................................................. 3-7 3.2.5 Reach 5 ............................................................................................................. 3-9 3.2.6 Reach 4 ........................................................................................................... 3-12 3.2.7 Reach 3 ........................................................................................................... 3-14 3.2.8 Reach 2 ........................................................................................................... 3-17 3.2.9 Reach 1 ........................................................................................................... 3-19 4 Implications for Restoration .......................................................................................... 4-1 4.1 Conditions of Geomorphic Process Functions and Fish Use in the Study Area .............. 4-1 4.2 Conceptual Restoration Project Types ............................................................................. 4-2 4.2.2 Riparian Enhancement ..................................................................................... 4-3 4.2.3 Floodplain and Off-Channel Habitat Reconnection .......................................... 4-4 4.2.4 Instream Structural Enhancement .................................................................... 4-4 4.3 Reach-Scale Priorities ...................................................................................................... 4-5 4.4 Summary of Restoration Needs and Opportunities .......................................................... 4-6 5 References ....................................................................................................................... 5-1 Appendices Appendix A Habitat Technical Report Appendix B Geomorphic Assessment of Lower Pilchuck River Appendix C Channel Profile of Lower Pilchuck River Appendix D Maps Appendix E Field and GIS Methods Appendix F Conceptual Project Designs December 2018, Final Cardno Table of Contents i Lower Pilchuck River Assessment Tables Table 2-1 Basic Reach Characteristics of the Lower Pilchuck River ............................................... 2-1 Table 2-2 Summary of Fish Habitat Data, Organized by Reach, from Data Collected 2016– 2018 (see Appendix A). ................................................................................................... 2-4 Table 4-1 Relative Condition of Geomorphic Process Functions in the Lower Pilchuck River, by Reach. ............................................................................................................... 4-1 Table 4-2 Additional Factors to Prioritize Restoration Opportunities ............................................... 4-2 Table 4-3 Categories of Restoration Actions and Project Types1 .................................................... 4-2 Table 4-4 Summary of Recommended Priority Restoration Actions.............................................. 4-55 Figures Figure 1-1 The Lower Pilchuck River, constituting the Study Area for this report. ............................ 1-2 Figure 2-1 Mainstem Lower Pilchuck River temperatures for summer 2016.. .................................. 2-5 Figure 3-1 Reach 8 overview maps. .................................................................................................. 3-3 Figure 3-2 Representative view of the reach near the head of Reach 8 (looking downstream) ....... 3-4 Figure 3-3 Major cliff/gully system near the bottom of Reach 8 (looking downstream). ................... 3-4 Figure 3-4 Reach 7 overview maps. .................................................................................................. 3-5 Figure 3-5 View of relatively unconstrained, modern floodplain in the lower portion of Reach 7. ...................................................................................................................................... 3-6 Figure 3-6 Reach 6 overview maps. .................................................................................................. 3-7 Figure 3-7 Area of relatively unconstrained active channel migration and gravel deposition, lower Reach 6 (looking upstream). .................................................................................. 3-8 Figure 3-8 Reach 5 overview maps. .................................................................................................. 3-9 Figure 3-9 Downstream view of confined channel near head of Reach 5. ..................................... 3-10 Figure 3-10 Log accumulation near the lower end of Reach 5 in an area of relatively active meandering. ................................................................................................................... 3-11 Figure 3-11 Reach 4 overview maps. ................................................................................................ 3-12 Figure 3-12 Reach 4 looking downstream toward the US Highway 2 crossing (just out of view). .............................................................................................................................. 3-13 Figure 3-13 Reach 3 overview maps. ................................................................................................ 3-14 Figure 3-14 Area of active channel migration in the upper part of Reach 3 (view downstream). ..... 3-15 Figure 3-15 US Highway 2 runoff entering the Lower Pilchuck River (foreground, flowing left to right) near the bottom of Reach 3. ............................................................................. 3-15 Figure 3-16 Change in stage for a constant discharge range at USGS gage 12155300 (Three Lakes Road bridge). ....................................................................................................... 3-16 Figure 3-17 Reach 2 overview maps. ................................................................................................ 3-17 Figure 3-18 Downstream view in mid-Reach 2, with outcrop of the resistant terrace sediments confining the RB of the river in this area. ....................................................................... 3-18 Figure 3-19 Limited area of channel migration and lateral bar development, in lower Reach 2 ....... 3-18 ii Table of Contents Cardno December 2018, Final Lower Pilchuck River Assessment Figure 3-20 Reach 1 overview maps. ................................................................................................ 3-19 Figure 3-21 Wood accumulation at the sharp bend in the river just downstream of the 2nd Street bridge. .................................................................................................................. 3-20 Figure 3-22 Armored, confined channel downstream of the Old Snohomish-Monroe Road crossing. ......................................................................................................................... 3-20 Figure 4-1 Bank protection under construction along Orchard Avenue, August 2018. ..................... 4-3 December 2018, Final Cardno Background and Purpose iii Lower Pilchuck River Assessment This Page Intentionally Left Blank iv Table of Contents Cardno December 2018, Final Lower Pilchuck River Assessment 1 Background and Purpose The Pilchuck River, a tributary