(a) Floodway (F1).
(1) Within any floodway area (F1), no encroachments, including fill, new construction, substantial improvements, repair of substantial damage, or other development shall be permitted unless it has been demonstrated through hydrologic and hydraulic analysis performed in accordance with standard engineering practice that the proposed encroachment will not result in any increase in the Base Flood Elevation.
(2) Because floodways present increased risk to human life and property due to their relatively faster and deeper flowing waters the Floodway shall be preserved to the greatest extent possible.
(3) New development shall not be permitted in the floodway where reasonable alternatives exist elsewhere. In addition to the requirements below the applicant shall demonstrate that there are no reasonable alternatives other than the floodway encroachment before a permit is issued.
(4) When the floodway is the only reasonable alternative the applicant shall demonstrate that the floodway encroachment is the minimum necessary to accomplish the project.
(5) All permitted uses, activities, and development shall be undertaken in strict compliance with the flood proofing and related provisions contained herein, and in all other applicable codes, ordinances and regulations.
(b) Floodway Fringe (F2) and Approximated Floodplain (F4).
(1) In the Floodway Fringe (F2) and Approximated Floodplain (F4), any development and/or use of land shall be permitted provided that all such uses, activities and/or development shall be undertaken in strict compliance with the floodproofing and related provisions contained herein and in all other applicable codes, ordinances and regulations.
A. In the Approximated Floodplain (F4) the Floodplain Manager shall review, or shall cause to be reviewed, proposed development less than ten (10) lots or two (2) acres to ascertain the specific flood risk at the building site and assign a "minimal, moderate or significant” risk level.
1. Development determined to represent a minimal risk and costing less than $10,000 shall be required to provide "Point on Boundary" elevation data and historic flood heights. The Floodplain Manager shall attempt to determine a height that will be reasonably safe from flooding using this elevation data. The Floodplain Manager shall enter the flood height in Section "G" of the Elevation Certificate. Any new or substantially improved structures using the "point on boundary" method (other than appurtenant structures) shall be required to have the lowest floor elevated at least three (3) feet above the highest adjacent grade even if the collected elevation data would indicate a lower flood elevation. If this method is not adequate to allow the Floodplain Manager to confidently determine the flood height the applicant shall be required to utilize one of the methods set forth below.
2. Development determined to represent a low to moderate risk and/or costing less than $30,000 shall provide Quick-2 engineering data prepared by a registered professional engineer or obtain free LOMA data from FEMA. This semi- detailed method will be used by the Floodplain Manager to determine a "Community Flood Elevation". The Floodplain Manager shall enter the "Community Flood Elevation" in Section "G" of the Elevation Certificate.
3. Development determined to represent a high risk and/or costing more than $30,000 shall be required to develop a Base Flood elevation using a detailed method such as HEC- ras. This data shall be prepared and certified by a registered professional engineer, who shall certify that the methods used correctly reflect currently accepted technical concepts. The resultant study shall include a cover letter, signed by the responsible professional, providing a statement of findings in basic terms and a completed Elevation Certificate. In addition, studies, analyses, computations, etc. shall be submitted in sufficient detail to allow a thorough technical review by the Floodplain Manager. Base Flood Elevations determined using this method can be used to rate flood insurance, typically resulting in a reduced premium.
(2) All subdivision proposals and other proposed new developments which are proposed to take place either fully or partially within the Approximated Floodplain area (F4) and which are greater than ten (10) lots or two (2) acres, whichever is the lesser, shall include base flood elevation data.
A. This data may be available from an authoritative source, such as the U.S. Army Corps of Engineers, U.S. Geological Survey, Natural Resource Conservation Service or state and local water resource department.
B. If the required data is not available from other sources the applicant shall develop the technical data using detailed methodologies comparable to those contained in a Flood insurance Study. This data shall be prepared and certified by a registered professional engineer, who shall certify that the methods used correctly reflect currently accepted technical concepts.
(c) AE area without floodway (F3). Within any AE area without floodway, no new construction or development shall be allowed unless it is demonstrated through a hydrologic and hydraulic study that the cumulative effect of the proposed development, when combined with all other existing and anticipated development, will not increase the elevation of the 100-year flood more than one (1) foot at any point. This requirement can be satisfied by utilization of the floodway area where determined.
(d) Alteration or Relocation of a Stream.
(1) Whenever a developer intends to alter or relocate a stream within the Floodplain Area the developer shall notify in writing, by certified mail, the City of Dunbar, Floodplain Administrator, The State Coordinating Office, and any adjacent communities of all such intended activities prior to the alteration or relocation of the stream. Copies of all required notifications must be submitted to the Federal Insurance Administration. In addition prior to issuing the local permit the Floodplain Administrator shall require copies of all necessary permits from those governmental agencies from which Federal or State Law requires approval. Contact information for State and Federal permitting authorities as well as addresses for required notification of appropriate County, State and Federal government agencies are contained in the City of Dunbar Stream Alteration administrative procedures.
(2) The developer shall also assure the City of Dunbar in writing that the carrying capacity within the altered or relocated portion of stream will be maintained. The Floodplain Administrator may require the applicant to demonstrate that the altered or relocated portion of stream will provide equal or greater conveyance than the original stream segment. If hydrologic and hydraulic analyses are required, they shall only be undertaken by a registered professional engineer, who shall certify that the methods used correctly reflect currently accepted technical concepts. The resultant study shall include a cover letter, signed by the responsible professional, providing a statement of findings in basic terms. In addition, studies, analyses, computations, etc. shall be submitted in sufficient detail to allow a thorough technical review by the Floodplain Administrator.
(3) Alteration of a stream includes placement of culverts, bridges or other stream crossings. The Floodplain Administrator may require the use of "best practice" techniques in the construction of bridges, culverts or stream crossings to prevent damage, loss of stream crossings and localized flooding caused by blockage. These techniques may include, but are not limited to, wing walls, trash grates or requiring openings to be of sufficient size to pass debris and/or anticipated future increases in flood heights.
(4) All new and replacement bridges, culverts and other stream crossings shall adhere to the relevant anchoring requirements contained in this article.
(5) The developer is required to provide the community a legal agreement detailing all scheduled inspections and maintenance to be performed on altered or relocated watercourses including culverts, bridges and other stream crossings. It shall be the responsibility of the applicant to transfer this agreement when the land associated with the watercourse alteration is transferred. A copy of all new agreements shall be provided to the Floodplain Administrator. Failure to transfer the agreement and provide a signed copy to the Floodplain Administrator shall subject the violator to the penalties set forth in Section 1749.08
(c).
(6) The applicant must submit any maps, computations or other material required by the Federal Emergency Management Agency (FEMA) to revise the Flood Insurance Study and/or Flood Insurance Rate Maps, when notified by the floodplain Administrator, and must pay any fees or other costs assessed by FEMA for this purpose.
(Ord. 623. Passed 11-19-07.)