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The DFIRM is a composite of several flood studies, some dating back to the 1970s and as recent as 2016 that represent the best available date at the production deadline. The exception to this is the "secluded areas" that are near significant levees that effect the floodplain do not meet the federal standard (44 Code of Federal Regulations 65.10) to show an area protected by the levee. The secluded areas, in the lower Puyallup River and the Carbon River and Puyallup River near the City of Orting, continue to show the understanding of risk prior to the establishment of 44CFR65.10 as shown on the first FIRM. There are more recent hydraulic studies that show a better understanding of flood risk and Unincorporated Pierce County regulates to this better data which has been added to the RegulatedFloodplain 2017 feature class(note that the secluded area has not been updated in the other mapped jurisdictions). In areas where the regulated flood hazard varies from the DFIRM there are attributions indicating a different "insurance zone" or "insurance BFE".
There is an attribution change that varies from FEMA standard for Zone X (shaded) areas. FEMA has several meanings for Zone X (shaded) areas some of which are regulated under county code (e.g. 1% annual chance flood in basins smaller than one square mile) and some that are not (e.g. the 0.2% annual chance flood area calculated in an approved detailed flood study). The Regulated Floodplain 2017 feature class differentiates these various risk so it can reflect in the symbology and to ensure non-regulated areas do not inadvertently trigger a county development permit review.Similarly the county regulates coastal hazard areas where wave action can cause damage. The Regulated Floodplain 2017 feature class has an attribute for “coastal”flood A and V zones. Not all saltwater flood hazard areasare “coastal”hazards as they are protected from significant wave action. There is also an attribute for flood hazard areas where the source of flooding is primarily groundwater.
The Digital Flood Insurance Rate Map (DFIRM) Database depicts flood risk information and supporting data used to develop the risk data. The primary risk classifications used are the 1-percent-annual-chance flood event, the 0.2-percent-annual- chance flood event, or areas with a watershed less than one square mile, and areas of minimal flood risk. The DFIRM Database is derived from Flood Insurance Studies (FIS), previously published Flood Insurance Rate Maps (FIRMs), and flood hazard analyses performed in support of the FISs and FIRMs, and new mapping data, where available. The FIS and FIRMs are published by the Federal Emergency Management Agency (FEMA). The file is georeferenced to earth's surface using the UTM projection and coordinate system. The specifications for the horizontal control of DFIRM data files are consistent with those required for mapping at a scale of 1:12,000.
The FIRM is the basis for floodplain management, mitigation, and insurance activities for the National Flood Insurance Program (NFIP). Insurance applications include enforcement of the mandatory purchase requirement of the Flood Disaster Protection Act, which "... requires the purchase of flood insurance by property owners who are being assisted by Federal programs or by Federally supervised, regulated or insured agencies or institutions in the acquisition or improvement of land facilities located or to be located in identified areas having special flood hazards, " Section 2 (b) (4) of the Flood Disaster Protection Act of 1973. In addition to the identification of Special Flood Hazard Areas (SFHAs), the risk zones shown on the FIRMs are the basis for the establishment of premium rates for flood coverage offered through the NFIP. The DFIRM Database presents the flood risk information depicted on the FIRM in a digital format suitable for use in electronic mapping applications. The DFIRM database is a subset of the Digital FIS database that serves to archive the information collected during the FIS.
Updates:
- Re-labeled FLD_ZONE field as "Regulatory_Zone". Populated "Insurance_Zone" field with most up-to-date FIRM information. Added "See King County FIRM" to Regulatory_Zone and Insurance_Zone fields for areas within Pierce County that are shown on the King County FIRM. (05/2020)
- Modified the flood zone (FLD_ZONE) attribute for certain “AE” flood hazard areas to “AE Coastal” to indicate where PPC 18E.70.040.E regulations apply. (04/2020)
The October 2019 update to the Regulated Floodplain 2017 shows the changed flood hazard areas modified by FEMA in two Letter of Map Revisions -LOMR.
Some coastal areas of Puget Sound were modified by LOMR 19-10-0588P that became effective 4/22/2019
A new flood study of Deer Creek within the City of Puyallup modified the flood hazard areas with LOMR 18-10-0841P that became effective 4/4/2019