KPFF Consulting Engineers 12/30/2021

Later Phase Eclipse Mill Project Task 400 River Hydraulic Analyses (BlueCoast Engineers) 400.1 Hydrodynamic Modeling The CONSULTANT shall utilize an available two-dimensional (2D) hydrodynamic model of the Snohomish River, developed by Snohomish County (Watershed Science and Engineering, 2021), to evaluate current velocities and water levels at the project site. The county's model is a 2D HEC-RAS model, which is a model platform developed by the USAGE that is commonly used for predicting water levels and current velocities in tidally influenced rivers. The existing model may be modified to increase the resolution along the project shoreline, if needed. The CONSULTANT shall develop a list of hydrodynamic scenarios that will be used in the modeling. These scenarios will be developed in coordination with the CONSULTANT Team and the CITY with the purpose of supporting design of the soft shoreline solution(s) and other in-water elements. These scenarios will include combinations of flow in the Snohomish River and tidal conditions (water levels) downstream. Up to 5 scenarios will be developed for use in the modeling work. CONSULTANT will conduct up to 20 model simulations based on the 5 hydrodynamic scenarios (maximum) and both existing and proposed (with-project) conditions. This includes up to 3 options for soft shoreline stabilization (see Subtask 600.01.6). The results of the modeling will be used to complete the following: • Select and optimize the preferred alternatives for the soft shoreline stabilization solution (see Subtask 600.01.6). • Evaluate potential changes to hydrodynamic conditions in the river at and adjacent to proposed project elements, including soft shoreline stabilization, docks and floating debris deflector. Modifications to these project elements may be proposed to minimize these predicted changes, if found. • Develop design criteria for 60% design of the soft shoreline stabilization solution and other in-water elements, as needed. The CONSULTANT shall develop a report that summarizes the modeling work and outlines the hydrodynamic design criteria developed for the project. 400.2 No Rise Analysis CONSULTANT will use the existing proposed conditions model (developed as part of this work) to evaluate zero rise in the Snohomish River adjacent and just upstream of the project location. CONSULTANT will develop a zero rise memorandum to document this work and to assist in permitting. DELIVERABLES: 1. Draft and Final Modeling Summary Report (PDF) 2. No Rise Memorandum (PDF) ASSUMPTIONS: 1. The existing model provided by Snohomish County is appropriate and adequate for use in design of the project.