No development shall result in any new or additional expense to any person other than the developer for flood protection; or 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.
(A) Analysis and design. Analysis and design of all stormwater facilities for the development shall comply with the standards and criteria established in any applicable watershed plan or interim watershed plan.
(B) Building permits. Stormwater facilities shall be functional before building permits are issued for residential or nonresidential subdivisions. The village may make the determination that building permits may be granted prior to the facilities being functional based on sound engineering.
(C) Overland flow paths. The development shall have an overland flow path at the downstream limit of the site that will pass the base-flood flow without increasing flood damage. If the upstream drainage area is less than 20 acres, a storm sewer pipe and inlet sized for the base flood may 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), without use of storm sewer capacity, at a minimum of one cubic foot per second per tributary acre, and without damage to structures.
(D) Protection of buildings. All usable space in new buildings or additions to existing buildings hydraulically connected to a major stormwater system, site runoff storage facility or overland flow path shall be elevated, floodproofed or otherwise protected to the FPE.
(E) Depressional storage. The function of existing onsite depressional storage shall be preserved for both onsite and offsite tributary flows in addition to required detention. When depressional storage is removed, it must be compensated for in the site runoff storage facility at a one-to-one ratio, 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 requirements as identified in this subchapter. The village 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, using a two-year through 100-year critical duration analysis.
(Ord. 2019-03, passed 4-15-2019)