APPENDIX C South Fork Skykomish River Geomorphic Assessment GEOMORPHIC ASSESSMENT SOUTH FORK SKYKOMISH RIVER Prepared for King County Department of Natural Resources and Parks River and Floodplain Management Section Prepared by Herrera Environmental Consultants, Inc. GEOMORPHIC ASSESSMENT SOUTH FORK SKYKOMISH RIVER Prepared for King County Department of Natural Resources and Parks River and Floodplain Management Section 201 S. Jackson Street, Suite 600 Seattle, Washington 98104 Prepared by Herrera Environmental Consultants, Inc. 2200 Sixth Avenue, Suite 1100 Seattle, Washington 98121 Telephone: 206/441-9080 December 19, 2012 CONTENTS Introduction ................................................................................................. 3 Assessment Area Limits .............................................................................. 3 Methodology ................................................................................................. 7 Existing Information .................................................................................. 7 Physical Setting ................................................................................ 7 Geologic Context ......................................................................... 7 Predevelopment Geomorphic Processes ............................................... 8 Reach-specific Geomorphic Conditions ................................................ 8 Field Studies ........................................................................................... 8 Habitat Impairments ........................................................................... 9 Natural Habitat Limitations ............................................................. 9 Human Modifications ..................................................................... 9 Observed Habitat Features ................................................................... 9 In-Channel Aquatic Habitats ........................................................... 10 Off-Channel Aquatic Habitat Types ................................................... 11 Observed Restoration Opportunities ....................................................... 12 Results ...................................................................................................... 13 Existing Information ................................................................................. 13 Physical Setting ............................................................................... 13 Geologic Context ........................................................................ 13 Predevelopment Geomorphic Processes .............................................. 15 Reach-specific Geomorphic Conditions ............................................... 16 Field Studies .......................................................................................... 21 Habitat Impairments .......................................................................... 21 Natural Limitations ...................................................................... 21 Human Modifications .................................................................... 22 Observed Habitat Features .................................................................. 37 In-Channel ................................................................................ 37 Off-Channel ............................................................................... 53 Observed Restoration Opportunities ....................................................... 53 Summary of Findings ...................................................................................... 63 References ................................................................................................. 65 Appendix 1 Information Sheets i jr 10-04766-019 geomorphic assessment-s fork skykomish TABLES Table 1. Aquatic Habitat Types Identified Within the South Fork Skykomish River Corridor. ........................................................................................ 10 Table 2. Summary of Armoring Length and Percentage by Reach. ............................... 19 Table 3. Summary of Potential Restoration Projects Identified During This Assessment. .................................................................................... 61 FIGURES Figure 1. South Fork Skykomish River Assessment Area. ............................................. 5 Figure 2. South Fork Skykomish River Longitudinal Profile. ........................................ 14 Figure 3. Illustration of a Typical Incised Reach Near Skykomish and a More Unusual Example of an intact Side Channel Near the Town of Baring. .......................... 17 Figure 4. Lacustrine Clay Exposed Along the Banks of the South Fork Skykomish River. ....... 22 Figure 5. Observed Human Modifications on the South Fork Skykomish River, Washington. .................................................................................... 23 Figure 6. Observed Geomorphic and Habitat Features on the South Fork Skykomish River, Washington. ............................................................................ 39 Figure 7. Potential Restoration Project Map, South Fork Skykomish River, Washington. ...... 55 ii jr 10-04766-019 geomorphic assessment-s fork skykomish INTRODUCTION This technical memorandum outlines the approach, analytical methods, and results of a geomorphic assessment that includes identification of restoration opportunities on the entire South Fork Skykomish River (the South Fork), from its headwaters at the confluence of the Tye and Foss rivers to its terminus at the confluence with the North Fork Skykomish River (the North Fork) near the Town of Index (Figure 1). This technical memorandum is part of a larger feasibility study of salmonid habitat restoration projects within the South Fork basin conducted by King County (the County). This larger feasibility study includes work and project identification on major South Fork tributaries, and a site-specific analysis of the lower Miller River Fan. The feasibility study is intended to be the first step in a process to improve habitat conditions and reduce flood and erosion risks in the South Fork. This geomorphic assessment describes the physical and ecological basis for restoration of predevelopment geomorphic conditions and improvement of in-stream habitat in the South Fork. The focus of the assessment is on habitat for anadromous fish, including Chinook, coho, steelhead and bull trout. The assessment is then the basis for the development of specific restoration opportunities, identified during the field work conducted as a part of the assessment. The assessment follows a physical-process-based approach, which has been suggested by many researchers for assessments of this kind (Kondolf et al. 2006; Beechie et al. 2010). The purpose of the identifying projects in this assessment is not to evaluate these projects, but merely to identify potential actions that could restore habitat conditions and predevelopment geomorphic functions. Details regarding the design and implementation of restoration actions are beyond the scope of this document. This assessment explicitly does not include a formal analysis of the hydrology of the basin, hydraulic modeling, a detailed analysis of the fish utilization of the area, or a delineation of large woody debris (LWD). Because a formal survey of all in-channel LWD has not been made, it was not possible to recommend LWD placement locations. Nonetheless, LWD could be added anywhere within the study area and would improve habitat quality, provided that care is taken to ensure that the added wood does not affect flood protection or cause other off- site impacts. Assessment Area Limits The assessment area for this portion of the feasibility study extends between the confluence of the Tye and Foss Rivers to the confluence of the South Fork and the North Fork near the town of Index, Washington. It includes the mainstem of the South Fork, its side channels, and the tributary junctions of its major tributaries, which include the Foss River, Beckler River, Anthracite Creek, Maloney Creek, Miller River, Money Creek, Barclay Creek, Index Creek, Bridal Veil Creek and Philadelphia Creek. The assessment area covers nearly 20 miles of river, December 2012 Geomorphic Assessment—South Fork Skykomish River 3 which were observed over the course of 4 days, 3 of which were by boat. As a result of the speed of the field reconnaissance, exhaustive, detailed observations of geomorphic features (such as bar sizes) were not possible. The primary intent of the field reconnaissance was to identify possible restoration projects, and to describe how science informed the prioritization of those projects. December 2012 4 Geomorphic Assessment—South Fork Skykomish River 1452000 1458600 1465200 1471800 1478400 1485000 1491600 1498200 1504800 1511400 1518000 1524600 Figure 1. South Fork Skykomish River North Fork assessment area, King County, Skykomish Skykomish River Washington. 303600 River 303600 (! Town of Index Sunset Falls Canyon Falls Legend 297000 297000 Eagle Falls South Fork Skykomish River ! ( (! North Fork Mount Baker Snoqualmie Reach break Reach National Forest Falls Reach (! River or creek Mt Index Barclay River sites 290400 Creek 290400 Highway Bridal Veil Philadelphia Railroad Creek Creek SNOHOMISH BPA powerlines Barclay Reach Community boundary 283800 KING 283800 Sunset Falls County boundary Town of Mount Baker Snoqualmie NF Baring 277200 277200 Baring Reach Index Creek South Fork 270600