Laserfiche WebLink
2 <br /> Scope of Work <br /> City of Everett Water Pollution Control Facility Outfall 025 Pre-Design Study <br /> 2-D Hydrodynamic and Sediment Transport Modeling and Design <br /> WEST Consultants,Inc. <br /> 12509 Bel-Red Road,Suite 100 <br /> Bellevue,WA 98005 <br /> Background and Understanding <br /> To support URS Corporation(URS),WEST Consultants,Inc. (WEST)will conduct <br /> hydrodynamic and sediment transport modeling to predict short-term, annual,and long- <br /> term sedimentation patterns and quantities near Outfall 025 in the Snohomish River and <br /> make recommendations regarding the need for and/or frequency of maintenance <br /> dredging. Sediment transport modeling will be performed for two outfall alternatives, <br /> including: <br /> • Alternative 2a:Relocate diffuser near the shoreline along original alignment <br /> • Alternative 2b:Relocate diffuser downstream along new alignment downstream <br /> of the I-5 Bridge <br /> The sediment transport model results will then be analyzed to provide information that is <br /> needed for URS and the City of Everett(City)to evaluate a preferred alternative. <br /> Figure 1 shows the outfall locations of the two proposed alternatives. For Alternative 2a, <br /> the outfall is located near the right(looking downstream)bank of the Snohomish River. <br /> As shown in Figure 2,the outfall is located at the inner side of a river bend,which is <br /> typically a sediment deposition zone due to the secondary flow around the bend. Flow <br /> along this reach is highly two-dimensional(2-D). In addition, Alternative 2a calls for a <br /> rock weir or vane to be placed upstream of the outfall. The streambed near the outfall <br /> will be excavated. While the vane will provide sufficient water depth in the vicinity of <br /> the outfall,the lower velocity near the outfall(downstream of the vane)will likely result <br /> in increased deposition as sediments tend to move towards the right(convex)bank again <br /> due to the secondary flow effect. The deposition pattern and rate are directly affected by <br /> the configuration of the vane. A 2-D hydrodynamic and sediment transport model will be <br /> able to simulate the complex flow field and the resultant bed deposition and erosion in <br /> the vicinity of the vane,thus allowing us to.determine the configuration of the vane in <br /> such a way that sediment deposition near the outflow will be minimised. For these <br /> reasons,we propose to use a 2-D model to evaluate the hydrodynamics and sediment <br /> transport along this reach of the Snohomish River. <br /> WEST scope and costs for Outfall 025 Hydrodynamic and Sediment Transport Modeling l <br /> 10/15/2013 <br /> 32 <br />