1986-24 (2) - Laserfiche WebLink

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24-hour duration storm event; however, the applicant shall also provide data indicating the effects of a 25 -year frequency 24-hour duration storm event on the development project as proposed. The design of any off-site stormwater management system improvements shall be based upon a 25 -year frequency 24-hour duration storm event. The modified Type 2 SCS Rainfall Distribution shall be used. (2) The hydrologic computations for the stormwater management system shall be based on full hydrograph gen- eration for the development project and contributory area utilizing such methods as published by the Soil Conservation Service (USDA, SCS, "Natural Engineering Handbook", Section 4, Hydrology: 1972 and "Urban Hydrology for Small Watersheds", Technical Release No. 55: 1975). For projects of less than 12.0 acres, the rational method of runoff computation is satisfactory. The rainfall intensity -dura- tion curves provided in Appendix A, attached hereto, are hereby incorporated as a part of this ordinance and shall be used in making all required hydrologic computations. (3) Retention or detention with filtration of the runoff from the first 1" of rainfall shall be provided on site. Detention with filtration or retention shall be provided on site for additional stormwater runoff generated by the development project over and above that generated by the site prior to the proposed development unless there is a legal positive outfall available which has sufficient capacity to accept the additional runoff. (4) Retention or detention facilities shall be con- structed in such a manner as to maximize utilization of available percolation capabilities on the site for recharge enhancement and to minimize mosquito breeding by being shallow, shall be easy to maintain, and shall have a 6X¢¢1 (400: skimmer mechanism if required by the SJRWMD. Stormwater Management facilities shall not penetrate the groundwater table unless the following criteria are met: (a) The application provides a X///#tib///'�///A�l�/d//1//��K,�,�kbk water quality certification from the SJRWMD or � ¢ 11(O bjf($)f¢(X//S�d h1ge Florida DER that the direct connection to the groundwater table, as proposed, will not significantly detract from the quality of the groundwater. If the size of the development project is below SJRWMD or DER thresholds, this certifi- cation can be waived; (b) Dry retention/detention at the site is not appropriate. The applicant's engineer or groundwater hydrologist shall provide a certified statement that soils are not suitable for dry retention/detention. Site support- ing soils testing shall be included,