(A) Requirements applicable to all developments. No development shall:
(1) Result in any new or additional expense to any person other than the developer for flood protection; or
(2) Increase flood elevations or decrease flood conveyance capacity upstream or downstream of the area under the ownership or control of the developer. This requirement shall not prohibit the removal or reduction of built obstructions to flow, such as increasing culvert capacity or lowering roadway elevations.
(B) Building permits. Stormwater facilities shall be functional before building permits are issued for residential and nonresidential subdivision.
(C) Single parcel developments. Stormwater facilities shall be functional where practicable for single parcel developments before building construction begins.
(D) Overland flow paths. The development shall have an overland flow path at the downstream limit of the property that will pass the base flood flow at a stage at least one foot below the lowest adjacent foundation grade in adjacent structures without increasing damage to structures or property. If the upstream drainage area is less than 20 acres, the storm sewer pipe and inlet sized for the base flood can be constructed in lieu of providing an overland flow path. Overland flow paths internal to the site shall be considered as part of the major stormwater system and shall be designed for conveyance of the base flood (critical duration) and shall be a minimum of one cfs per tributary acre without damage to structures.
(E) Protection of buildings. All usable space in new buildings or added to existing buildings hydraulically connected to a major stormwater system, site runoff storage facility or overland flow path shall be elevated, flood proofed, or otherwise protected to at least one foot above the blocked restrictor elevation of the site runoff storage (detention) facility or the calculated high water elevation of the overland flow path, or two feet above the base flood elevation, whichever is greater.
(F) Depressional storage. The function of existing on-site depressional storage shall be preserved for both on-site and off-site tributary flows in addition to required detention. When depressional storage is removed, it must be compensated for in the site runoff storage facility at one and one-quarter to one ratio if the depression is identified as a regulatory floodplain and at a one to one ratio if the depression is not a regulatory floodplain, provided that offsite areas tributary to the existing depressional storage are routed through the site runoff storage facility. This requirement is in addition to the site runoff storage required in § 164.023. The Chief Subdivision Engineer may allow the function of depressional storage to be preserved if the applicant performs detailed pre- and post-project hydrologic and hydraulic modeling to identify the effect of the depressional storage on discharges over a range of rainfall frequencies.
(Ord. 10-164, passed 6-17-2010) Penalty, see § 164.999