Drainage plans shall be approved by the City Engineer when it can be demonstrated that the proposed development activity has been planned and designed and will be constructed and maintained to meet each of the following standards:
(A) To maintain the natural flow regime and hydrologic characteristics of drainage basins each plan must include, at a minimum, the calculations for both predevelopment and postdevelopment conditions and the following design criteria:
(1) Storm water runoff characteristics (e.g., curve number, runoff coefficient).
(2) Seasonal high groundwater table elevations.
(3) Curve number selection and infiltration potential shall be based on a recommendation from an on-site analysis of site soils by a qualified geotechnical engineer. Infiltration potential and the extent of each soil type found on the site must be included.
(4) Time of concentration calculations. A minimum time of concentration of fifteen (15) minutes shall be used for commercial developments and minor street projects, and ten (10) minutes for all other developments.
(5) Design storm, including duration, frequency, precipitation and type of distribution, and shall be selected as follows:
(a) Ten (10) year, twenty-four (24) hour storm event for commencing development for subdivisions, shopping centers, commercial or industrial facilities.
(b) Twenty-five (25) year, twenty-four (24) hour storm event for any arterial, collector or major road projects; and subdivisions, industrial or commercial development of forty (40) acres or more.
(6) Stage-storage computations of any storage areas such as retention/detention facilities used, including the computations showing the effect of the design storm event.
(7) Stage-storage-discharge computations for any retention/detention facilities at the control point or any other point as required, (e.g., weir), including the computations showing the effect of the design storm event.
(8) Drawdown calculations for retention/ detention facilities to substantiate design. The drawdown calculation shall be based on a complete soils study by a qualified geotechnical engineer.
(9) Post-development peak rate of discharge shall not exceed predevelopment peak rate of discharge for the ten (10) year, twenty-four (24) hour or twenty-five (25) year, twenty-four (24) hour storm, whichever is the appropriate design storm.
(10) A description of the methodology, assumptions, parameters, and a copy of all such computations used to analyze the system shall be included with the submittal. If a computer program is used for the analysis, a copy of the computer printout shall be submitted to the city. The applicant must obtain approval from the City Engineer for any software used in the development of application materials.
(11) Complete description of measures to be implemented during the construction period to mitigate adverse quantity and quality impacts off-site.
(12) Any temporary construction which may affect the on-site and/or off-site storm water management system prior to completion of the project.
(13) Wet detention storm water management systems shall:
(a) Provide a treatment volume of the following:
1. One (1) inch of runoff from the entire site, or
2. Two and one-half (2½) inches of runoff from the impervious area (whichever is greater of the two).
(b) Be designed so that the outfall structures shall bleed down one-half (½) the volume of storm water specified in (a) above, within forty- eight (48) to sixty (60) hours following a storm event, but no more than one-half (½) of this volume will be discharged within the first forty-eight (48) hours.
(c) Contain a permanent pool of water sized to provide an average residence time of at least fourteen (14) days.
(d) Provide a littoral zone to be designed as follows:
1. The littoral zone shall be gently sloped (six to one (6:1) or flatter). At least thirty percent (30%) of the wet detention system surface area shall consist of a littoral zone. The percentage of littoral zone is based on the ratio of vegetated littoral zone to surface area of the pond at the control elevation.
2. The treatment volume should not cause the pond level to rise more than eighteen (18) inches above the control elevation.
(e) The option of utilizing a fifty percent (50%) increase in permanent pool volume in lieu of littoral zone.
(14) Development with no outfall available (landlocked) shall detain and treat its stormwater runoff on the site from a one hundred (100) year, twenty-four (24) hour design storm or according to SJRWMD 40C-4 criteria, whichever is more stringent.
(15) Computations showing that the spacing of inlets is in conformity with the maximum allowable water spread on pavement as defined in the city Public Works Manual.
(16) If an open channel or swale is used for conveyance, the side slopes shall be one (1) foot vertical drop for each two (2) feet or more of horizontal distance.
(17) The side slope on dry retention ponds shall be sodded and whenever possible the bottom should be sodded also or seed and mulched as minimum.
(18) A certification signed by the engineer, licensed in the state, responsible for the design which shall read as follows:
“I hereby certify that the design of the Stormwater Management System for the project known as (Project Name) meets all of the requirements and has been designed substantially in accordance with the requirements of the City of Palm Bay's Ordinance No. 95-33 and the Public Works Manual.”
(B) To protect or improve the quality of groundwaters and surface waters;
(C) To ensure that there is not more erosion after development than there was under natural or predevelopment conditions;
(D) To maintain groundwater levels;
(E) To protect the beneficial functioning of wetlands such as swamps, bogs, marshes, estuarines, sloughs, floodplains, water basins and salt meadows for the natural storage of surface waters and the biological reduction and assimilation of pollutants;
(F) To protect against damage by building in an area, the whole or part of which is subject to flooding, until the area is filled to the base flood elevation after settlement, as shown on the flood insurance rate map and/or the flood hazard boundary map with amendments; or elevate the structures such that the finished habitable floors are built to or above the applicable base flood elevation as shown on the flood insurance rate map and/or the flood hazard boundary map with amendments and have met the requirements of this chapter.
(G) To prevent saltwater intrusion by adhering to applicable best management practices;
(H) To minimize injury to vegetation, fish and wildlife habitat and otherwise help to attain the objectives of this subchapter.
(Ord. 95-33, passed 8-24-95) Penalty, see § 174.079