City Proposes Revisions to Granite Reef Wash 100-year Floodplain
Just like road maps are updated periodically, FEMA’s Flood Insurance Rate Maps are updated periodically to keep them up to date. Updates may be based on improved floodplain modeling techniques, changes within the watershed that result in increased or decreased rainfall runoff, and/or re-grading which affects floodplain hydraulics.
The City of Scottsdale, in partnership with the Flood Control District of Maricopa County and Salt River Pima-Maricopa Indian Community, is constructing storm drain improvements within the Granite Reef Wash watershed, which begins at the Arizona Canal and ends at the Salt River, and which generally lies between Granite Reef Road and the Loop 101 Freeway. These improvements, when completed will divert stormwater westward to Indian Bend Wash, which has adequate capacity to handle the additional runoff. Therefore, the 100-year peak flow rate for the entire watershed will be reduced. As a result, the 100-year floodplain for the Granite Reef Wash watershed will be generally smaller than what is depicted on FEMA’s current Flood Insurance Rate Maps (FIRMs). The City of Scottsdale retained an engineering consultant to revise the current floodplain maps accordingly, using state-of-the-art 2-dimensional floodplain modeling techniques. The new study, when adopted by FEMA, will result in the 100-year floodplain being removed from many properties, which will eliminate the mandatory flood insurance requirement pursuant to federal law for these property owners. Phase I of these improvements are complete at this time. The city continues to work towards the final design and construction of the Phase II improvements, with a target completion date of FY24-FY25.
The City of Scottsdale plans to schedule an open house public meeting during FY24-25 to discuss the proposed floodplain revisions and answer questions. Letters showing the proposed 100-year floodplain revisions for each parcel will be mailed to the affected property owners, inviting them to an open house public meeting. The date, time, and location of the open house public meeting will be posted in this web page in the future.
Below is the application (PDF) to FEMA to conditionally revise the Granite Reef Wash 100-year floodplain:
2. Hydrology, Hydraulics, Erosion, Sediment Transport, Geomorphis Analysis, Draft FIS Data
4.1 Appendix A – Drainage Results Exhibits
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