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' ' <br /> � I <br />'I <br /> [=LORIDA DEPARTMENT OF TRANSPORTATION (FDOT) <br /> � � <br /> The Walgreens site is in an area which outfalls into a closed basin. Accordingly, FDOT <br /> � has two requirements. First, the storage of the volume difference for the pre/post <br /> � <br /> development 100 year critical storm event must be provided. Half of the storage volume <br /> Imust be recovered in seven days and the total volume must be recovered within 30 days. <br /> Secondly, it is required that an emergency outfall is provided and that the post- <br /> � development peak discharge for the 100 year critical storm event be restricted to the 100 <br /> year pre-development peak discharge rate. The offsite drainage area's runoff will be <br /> � I <br /> convelyed via swales and/or on-site conveyance pipes to the existing FDOT basin/ outfall, <br /> I <br /> see Figure 3 - Pre-Development Plan. The following sections document that the <br /> ' propo'sed stormwater facility will comply with FDOT standards. <br /> � CLOSED BASIN DESIGN <br /> � � <br /> , The r i noff hydrographs for the pre- and post- development conditions show the amount of <br /> s tormwa ter runo ff, w hic h de termines t he pre/pos t vo lume di fference requirements. T he <br /> pre and post development hydrographs for the critical storm event (100 year, 10 day) are <br /> 1 ' <br /> focated in Appendix B (along with the 100 year 24 hour through the100 year 7 day <br /> � hydrographs - to show the critical event). The 100 year, 10 day pre development <br /> � <br /> hydrograph shows a runoff volume of 2.7 Acre-feet and the post development hydrograph <br /> , shows a runoff volume of 3.8 Acre-feet. <br /> � The f i Ilowing calculations show that the difference of the runoff volumes for the pre- and � <br /> j <br /> post i evelopment 100 year critical storm events are accommodated in the proposed <br /> � stormwater facility: <br /> ' 3.8 Ac-ft - 2.7 Ac-ft = 1.1 Ac-ft =47,916 cf <br /> , The proposed stormwater facility will have a top of bank at elevation 91.5 feet with <br /> , four to one side slopes to the bottom of the facility at elevation 84.5 feet. The <br /> volume difference is contained below an elevation of 90.5 feet as shown by the <br /> ; average end area method (calculation) below: <br /> ' <br /> ' CadM/,data/99/6001-99/6001-99drainage <br />