2025/06/04 Council Agenda Packet

Exhibit A (Scope of Work) • Problem Statement: Clearly define the problem or question the model aims to address (e.g., flood risk assessment, water distribution analysis). • Geographic Area: Specify the location and extent of the area being modeled • We assume the hydrologic model performed for the Surface Water Comprehensive Plan does not need to be updated, flows will be extracted from the existing, and worse -case future, conditions; however, if development in the basin requires updating the hydrologic modelling, Otak would request a contract amendment • Model Type: SRH - 2D steady state • Hydraulic analyses will extend from Mukilteo Boulevard to the 3000 feet downstream to outfall in Port Garnder Bay; to assess potential impacts off the project such as flooding, channel erosion or deposition, or impacts to critical habitat • Otak will set up an existing conditions plan, and one proposed condition plan to support preliminary design; if iterations are needed to refine the proposed conditions, that would be covered under a contract amendment • Otak will provide preliminary hydraulic results such as scour depth water flow depth, shear stress, velocity to Everett for use in streambed and structure low chord design • Otak has budgeted up to 24 hours to coordinate with the City on how to utilize the hydraulic results for design • Normal depth boundary condition will use hydraulic modeling • The preliminary design included in this task will be assessing an average slope/hydraulic condition with the culvert and immediately upstream and downstream of the culvert. We anticipate that during the 60% design, the habitat features and geomorphic plane form or stream type(s) such as cascading boulders and/or step-pools will be added in the culvert, as well as upstream and downstream of the culvert. The habitat features may include a deformable bed design, to support in culvert meander bars and the installation of habitat features such as woody structures and boulders. Refinement of the preliminary hydraulic model to support the 60% design is not included in our scope and fee; Otak can add this as an amendment if needed, or the City can update the mode l TASK 5.1 DELIVERABLES • Fish Passage Basis of Design Memorandum which includes: o Key Findings: Summarize the key findings of the modeling study. o Visualization: Present the model results in a clear and concise manner (e.g., maps, tables, graphs). o Interpretation: Interpret the model results and their implications for the problem being addressed. 5.2 Alternatives Analysis Two culvert alternatives will be prepared to compare culvert structure type for the culvert replacement. OTAK will evaluate suitable foundation types for the culvert(s) based on the geotechnical investigation. The pros and cons of each alternative will be provided with a comparison table, and a recommendation for a preferred alternative. The comparison table will include culvert capital construction costs, potential utility conflicts and relocation, public safety, construction challenges, maintenance consid erations and ease of permitting. In addition to the comparison table the design criteria and any expected variances and 10% concept drawings will be documented in an alternatives analysis technical memorandum.