In early 2010, the City began a study to model the floodplain of the Willamette River in North Albany. The study was initiated because the current FEMA floodplain maps for North Albany appeared to be inaccurate. The most significant inaccuracy was an unmapped floodway. In order to adequately review future development proposals and for the development community to know what challenges might exist on an existing parcel prior to investing in development, it was important to have a more accurate assessment of floodplain characteristics throughout North Albany
The North Albany floodplain study verified that there was a significant unmapped floodway through North Albany. This floodway is essentially an overflow channel from the Willamette River. It is estimated that, during a 100-year flood event, approximately 5,600 cubic feet per second (cfs) of water flows through this floodway at a maximum speed in excess of five feet per second. To put that amount of water in perspective, it is what typically flows in the Willamette River itself in September. At five feet per second, water with very little depth can apply enough force to push a car off of the road.
The study also unexpectedly identified significant differences in the amount of flooding throughout the study area. These differences were seen in both the extents and depths of flooding. When compared to FEMA’s most recent (2010) FIRMs, the study identified approximately 102 acres of property mapped as being in the floodplain that shouldn’t be and approximately 104 acres of property that should be shown in the floodplain but was not. Differences in the depths of flooding ranged from more than four feet less than the 2010 FEMA maps to around two feet more than the 2010 FEMA maps. The floodplain maps for North Albany were adopted by FEMA and the City in 2016 and became effective on December 8, 2016.
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