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Note: This description is provided for those interested in a technical description of the modeling process.

Hydraulic models were developed to evaluate the North Albany floodplain.   HEC-RAS was the primary model used, and FLO-2D was used to more accurately model much of the area east of Springhill Drive.  LIDAR (a technology that uses lasers to measure ground surface elevations from the air) data as collected by the state and ground survey data as collected by the consultant were used to generate detailed profiles of the ground surface.  This data was incorporated into the HEC-RAS model as was the Willamette River profile as predicted by FEMA during a 100-year flood event.  The 100-year flood levels were then run through the HEC-RAS model across the specific ground profile for North Albany in order to generate the consultant’s floodplain maps.

In the eastern region of North Albany the Willamette River wraps around the City and there are several flow exchange paths between the river and the lower elevations of North Albany.  Because of the complex nature of these flow exchange paths, the consultant created a 2D model using FLO-2D.   According to the FLO-2D website, FLO-2D is a dynamic flood routing model that simulates channel flow, unconfined overland flow and street flow.  It can simulate a flood over complex topography and roughness while reporting on volume conservations; the key to accurate flood distribution.  Use of this model helped to refine the model results and more accurately predict the expected flooding in this area.

It is important to note that the Willamette River itself was not remodeled.  However, the consultant has identified what it believes to be an error in FEMA’s Willamette River profile near the downstream end of our study area.  The consultant believes that the Willamette River itself would reach an elevation approximately 2 feet higher than what FEMA predicts (based on reviewing historical flood records).  The consultant has corrected this apparent error when they built their model, which is apparent in the model results by the increased flooding depths predicted in the north and east portions of the study area.

Although the Willamette River itself was not remodeled, the consultant did remap the flood boundaries and BFE contour lines based on evaluation of the published FEMA flood profiles. There was a need to redraw the boundaries along the river based on the unchanged profile of the Willamette, in order to properly transition from FEMA’s Willamette River flood profile to the adjacent modeled floodplain in North Albany.

All Model results were then compared to past aerial flood photos and historic river gauge data to verify results.