Ordinance 3129-09 - Laserfiche WebLink

Restoration and Land Use Concepts shown or would result in impacts that cannot be practicably mitigated. Alternative designs that maximize restoration based on the studies shall be consistent with the goals, objectives and policies in Section 4 of this Plan. This section describes the additional work that will be required in order for the subarea plan to be designed and implemented. 3.3.2.1.1 Studies Required There are several design considerations that will need to be further analyzed to take the subarea plan from its present planning level to the conceptual and final design levels. These studies include, but are not limited to: • Developing an unsteady hydraulic model for the subarea to understand how water flow will occur within the subarea during flood conditions compared to existing conditions, and how flood protection and drainage of private and non-restoration areas will be achieved. This will include analysis of flood elevations throughout all properties and expected differential levels and overtopping conditions across all existing and new dikes, including cross dikes, as the basis for dike stability analysis. The key analysis result will be the changes in flood levels for selected recurrence interval flood events and the level of protection afforded to adjacent properties not included in the action area. Modeling will also better define when and where sediment deposition and erosion will occur. • Developing a drainage study to determine how existing drainage patterns will be maintained for properties that are not included in restoration actions and that would no longer be connected to the pump station infrastructure. • Determining the degree to which any new dikes would affect existing floodplain elevations and flood flows. • Furthering various design elements including, but not limited to, whether channels will be excavated or allowed to form naturally and the precise and the final location and required size of the dike breaches and culverts to allow for tidal flushing while maintaining existing levels of flood protection. • Developing design standards for dikes and other project elements for geotechnical stability under the maximum expected differential water levels and expected overtopping conditions, including accommodation of potential sea level rise and changes to the Snohomish River hydrograph due to climate change impacts. Draft Subarea Plan June 2009 Everett Marshland 48 070346-01