(A) The placement of detention basins within the floodplain is strongly discouraged because of questions about their reliable operation during flood events. The use of fee in lieu of detention shall be investigated where detention outside of the floodplain is not feasible.
(B) However, the stormwater detention requirements of this chapter may be fulfilled by providing detention storage within flood fringe areas on the project site, provided the following provisions are met:
(1) Detention in flood fringe areas.
(a) The placement of a detention basin in a flood fringe area shall require compensatory storage for 1.5 times the volume below the base flood elevation occupied by the detention basin, including any berms.
(b) The release from the detention basin provided shall still comply with the requirements of this chapter.
(c) The applicant shall demonstrate its operation for all stream flow and floodplain backwater conditions up to the ten-year frequency flood elevation.
(d) Excavations for compensatory storage along watercourses shall be opposite or adjacent to the area occupied by detention.
(e) All floodplain storage filled below the existing ten-year frequency flood elevation shall be replaced below the proposed ten-year frequency flood elevation. All floodplain storage filled above the existing ten-year frequency flood elevation shall be replaced above the proposed ten-year frequency flood elevation. The additional storage volume (0.5 times the totals volume filled) may be provided at any elevation between the normal water elevation and the BFE.
(f) All compensatory storage excavations shall be constructed to drain freely and openly to the watercourse.
(2) Detention in floodways. Detention in floodways is prohibited.
(Ord. 07-02, passed 4-16-2007)