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4 <br /> b. How quickly are these channels moving laterally and what would expected lateral movement be over <br /> next 40 years? <br /> In order to answer these questions and help select the most appropriate design application for the repair of <br /> the pipeline crossings, the following analysis is necessary. The analysis was divided into three sections: <br /> data compilation and review, qualitative assessment and quantitative assessment. <br /> Data compilation and review: <br /> • Topographic base maps for each five crossing area and the overall project area—utilize existing <br /> LIDAR GIS data, that will be obtained from King County, which provides sewer service to the <br /> south part of Snohomish County, and is the repository for the GIS data that is required. <br /> • Obtain and review the following geomorphology and related reports <br /> — Snohomish River Basin Salmonid Recovery Technical Committee. 2004. Ecological <br /> Analysis for Salmonid Conservation[Draft]. Snohomish County Public Works <br /> — Haas, Andrew and Brian Collins, 2001. "A Historical Analysis of Habitat Alterations in the <br /> Snohomish River Valley, Washington, Since the Mid-19m Century: Implications for Chinook <br /> and Coho Salmon,"prepared by Tulalip Tribes/Snohomish County Public Works.February. <br /> • Obtain and review aerial photographs — stereoscopic coverage wherever possible (e.g., UW, <br /> Seattle District Corps of Engineers, USDA NRCS) <br /> • Research and obtain historical maps and accounts of major floods — UW Pacific Northwest <br /> Collection, UW map collection;Corps of Engineers <br /> • Obtain and review existing geotechnical boring logs—location and elevation referenced in GIS to <br /> determine if data can be used in lieu of sediment sampling <br /> • Obtain and review reports detailing the history of channel modifications in vicinity of crossings <br /> (revetment, levee construction,WSDOT activities,City of Snohomish) <br /> • Review hydrographer's records for USGS gauges @ Snohomish River and Pilchuck River for <br /> maximum available period <br /> • Review watershed assessments for representative tributaries (e.g., Pilchuck, Skykomish, <br /> Snoqualmie river basins) <br /> Qualitative assessment: - <br /> • Develop watershed conceptual model with respect to sediment supply from c.1960 to c.2040 <br /> • Qualitatively evaluate channel migration, avulsion risks from aerial photographs, channel <br /> bathymetry,hydraulic model, general understanding of river system <br /> • Qualitatively evaluate inundation extent from major floods using GIS data combined with <br /> hydrology and hydraulic models <br /> • Develop conceptual models for each of 5 sites <br /> Quantitative assessment: <br /> • Determine rates of lateral migration in vicinity of each of 5 sites <br /> • Quantify scour patterns with respect to flood events at gaging stations <br /> • Evaluate hydraulic model results (e.g., longitudinal trends in unit and total stream power) — this <br /> will utilize a GIS created longitudinal profile for each project location. <br /> In addition, the geomorphologist will work together with the hydraulic engineers to ensure <br /> hydraulic modeling acurately reflects the condition of each site. <br /> 13 <br /> K:\163\City of Everett Water Transm Pipeline Xings\Scoping and Costing\Scope&Cost Amendment 1\UP3148 URS Amend 1.doc(Y3 7/15/1999) <br />