The following policies relate to required floodplain information to be provided with subdivision drainage studies submitted to the town for approval. When applicable, exceptions to these policies may be made at the discretion of the Public Works Department under special conditions.
(A) Floodplain delineation.
(1) The developer shall be responsible for all submittals to FEMA, including fees, in the event that the boundaries of the floodplain or floodway change as a result of the proposed development. All subdivisions and development located wholly or partially within the FEMA regulated floodplain are required to show how the proposed development will affect existing floodplain or floodway boundaries. Development within the 500-year floodplain, as defined by FEMA, is exempt from this requirement.
(2) New subdivisions shall have 100-year floodplain and floodway delineations prepared using the 100-year 24-hour future condition peak discharge. If an existing FEMA floodplain delineation exists on the property proposed for a new development, the floodplain shall be redelineated based on the 100-year 24-hour future condition peak discharge. Resubmittal to FEMA will only be required if the intent is to decrease the width of the FEMA 100-year floodplain.
(3) Floodplain or drainage path delineations shall conform to the following normal size limitations:
(a) Detailed delineations: Drainage basin greater than 160 acres in size.
(b) Approximate delineations: Drainage basins between 40 and 160 acres.
(c) Drainage path: Drainage basins between 10 and 40 acres.
(4) The following items shall be done for those developments that will be located within a regulatory floodplain:
(a) A note on the Final Plat shall be included listing the minimum recommended finished floor elevations for all lots within the delineated 100 year floodplain. If any portion of the lot within the building envelope is within the 100 year floodplain, the entire lot is considered to be in the floodplain.
(b) The owner/developer shall have an Arizona Registered Civil Engineer or Land Surveyor certify the finished-floor elevations of all new structures located within the FEMA floodplain. In the case of manufactured homes, all elevations are related to the bottom of the structural frame or the lowest point of any attached appliances.
(5) Both existing FEMA and new floodplain and floodway delineations shall be clearly shown on Subdivision Plats.
(B) Floodplain encroachment. The following policies relate to proposed encroachments into an existing FEMA regulatory floodplain.
(1) Encroachments into the floodplain shall not cause the 100-year water surface elevation to rise more than one foot in elevation, or exceed the FEMA regulatory water surface elevation, whichever is less. This allowable rise in water surface will only be permitted if existing development will not adversely be affected by the rise in water surface elevation.
(2) No encroachments into the regulatory floodway are allowed within the town.
(C) Floodplain and floodway modeling methods. Any software used for hydrologic and hydraulic floodplain analyses must be approved by FEMA. The approved FEMA software list can be found at: http://www.fema.gov/MIT/TSD/EN_modl.htm.
(Res. 1637, passed 2-28-02; Am. Res. 2871, passed 9-17-15; Am. Ord. 872, passed 9-17-15)