Fisher's Hydraulics Building Addition
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Fisher’s Hydraulics Building Addition (5010 E Columbus Drive) Stormwater Management Report Revised March 07, 2017 Prepared for: Prepared by: 1000 N. Ashley Drive Suite 900 Tampa, FL 33602 (813) 620-4500 TABLE OF CONTENTS 1.0 INTRODUCTION ...............................................................................................................3 2.0 EXISTING CONDITIONS ....................................................................................................3 2.1 Ground Cover, Soils, and Wetlands ......................................................................3 2.2 Existing Conditions Drainage ................................................................................3 2.3 Floodplain ............................................................................................................4 3.0 PROPOSED CONDITIONS .................................................................................................4 3.1 Water Quality Treatment .....................................................................................4 3.2 Stormwater Attenuation ......................................................................................5 3.2.1 Southern Discharge (E Columbus Drive) ....................................................5 3.2.2 Western Discharge (Spreader Swale near I-4 on-ramp) .............................5 3.3 Floodplain Compensation ....................................................................................6 4.0 STORMWATER SYSTEM OPERATIONS .............................................................................6 4.1 Operation.............................................................................................................6 4.2 Maintenance ........................................................................................................6 4.2.1 Ditches and Swales ...................................................................................6 4.2.2 Inlet grates ...............................................................................................6 4.2.3 Pipes and Inlets ........................................................................................6 4.2.4 Retention/Detention Ponds ......................................................................7 4.2.5 Vegetation ................................................................................................7 4.2.6 Control Structures ....................................................................................7 4.2.7 Sediment Sumps Structures ......................................................................7 4.2.8 Contingency Planting Details for Wetland Impact Areas ...........................8 1 APPENDICES Appendix A Maps Location Map FEMA Flood Insurance Rate Map Aerial Appendix B NRCS Soils Map & Information Appendix C Existing Conditions Basin Map & Node-Link Diagram Appendix D Existing Basin CN & Tc Calculations Appendix E Existing Conditions ICPR Model - Input Data Appendix F Existing Conditions ICPR Model – Basin Summary Appendix G Existing Conditions ICPR Model – Node Max. Report Appendix H Proposed Conditions Basin Map & Node-Link Diagram Appendix I Proposed Basin CN & Tc Calculations Appendix J Proposed Conditions ICPR Model – Input Data Appendix K Proposed Conditions ICPR Model – Basin Summary Appendix L Proposed Conditions ICPR Model – Node Max. Report Appendix M FDEP Impaired Basin Exhibit Appendix N Treatment Calculations Appendix O Storm Tabulations [On-site and Off-site (incl. FDOT plans)] Appendix P 17th Ave. R/W Vacation Documents Appendix Q Proof of Ownership – Deeds Appendix R Disturbed Area Exhibit Appendix S Pond 100 By-pass Swale Capacity Computations 2 1.0 INTRODUCTION The Applicant operates a six-bay hydraulics repair shop located at 5010 E. Columbus Drive (near the intersection of US-41 and Interstate 4). The Owner wishes to expand operations by constructing a second repair shop on several existing vacant lots located immediately east of his current facility. The proposed building addition and associated site improvements will be incorporated into a single compound. The buildings will share site infrastructure as well as a unified stormwater management system. The existing repair facility is served by a ‘dry’ stormwater management facility that utilizes an Effluent Filtration System. In an effort to consolidate open space, the stormwater management system for the existing and proposed buildings will be combined into a single system located north of E. 17th Avenue. The proposed wet detention stormwater pond will have dual outfalls in order to mimic the existing condition drainage pattern (a spreader swale discharging to the west and a drop structure that utilizes the existing piped discharge connection to the E. Columbus Dr. municipal separate storm sewer system [MS4]). 2.0 EXISTING CONDITIONS 2.1 Ground Cover, Soils, and Wetlands A geotechnical investigation report dated July 31, 2016 was prepared by Driggers Engineering Services Incorporated (DESI) titled “Proposed Expansion 5010 Columbus Drive Hillsborough County, Florida”. The site investigation found a soil profile consisting of fine sands extending to the termination of boring (12 to 18 ft.). Soils throughout the profile were represented primarily by the SP to SP-SM Unified Soil Classification System (USCS) designation with some SM soils noted in the report. Seasonal High Water elevation noted in the Geotechnical report was influenced by rain events that occurred shortly before the field work was conducted and does not consider the impact of the site’s adjacency to the existing linear pond located adjacent to the I-4 on-ramp. In order to maintain sustainable water levels necessary to support the proposed littoral shelf, the proposed stormwater management system is designed with a control elevation equal to that permitted by FDOT with ERP 43-20690.01. The proposed consolidated stormwater management system has a proposed control elevation of 31.50 ft. (NAVD). There are no known wetlands located within the limits of proposed work. 2.2 Drainage The existing repair facility drains via sheet flow north to the stormwater management facility for water quality treatment and attenuation prior to being discharged into the City’s MS4 located within E Columbus Drive. Additionally, the existing undeveloped lots located between the 3 existing repair shop and N. 51st Street drain to a headwall that is connected to the pond outfall pipe and discharges to the E Columbus MS4. The area north of E. 17th Avenue generally drains west-northwest via sheet flow to the existing linear pond located adjacent to I-4. The presence of a driveway cut onto E. Columbus Drive indicates that the proposed project area has been previously developed. However, since historical aerial photographs indicate that it has been vacant since before 1995, the stormwater management design is based on this area being pervious in the existing conditions. The discharge rates associated with the existing stormwater pond were determined by creating an ICPR model using survey data to compute existing storage volume and the dimensions associated with various reaches. Table 2.1 – Pre-Development Peak Inflow into Boundary Nodes 5-yr/24-hr Inflow Rate Node Notes (cfs) Columbus 5.74 Pond 800-3 6.31 2.3 Floodplain Based on the Federal Emergency Management (FEMA) Flood Insurance Rate Map (FIRM) panel #12057C0359H effective August 28, 2008 (refer to Appendix A), the project is located within Zone ‘X’ (areas outside the 0.20% annual flood probability). 3.0 PROPOSED CONDITIONS The proposed stormwater management facility is designed to provide pre/post attenuation for the 25-yr/24-hr storm event so that post development discharge rates do not exceed those occurring in the existing conditions. This pre/post attenuation criteria was applied to both of the proposed ponds discharge points and proposed discharge rates are included in Appendix L for your review. 3.1 Water Quality Treatment The project site is located within the ‘Uceta Yard Drain’ basin (WBID 1599). This WBID is impaired for Fecal Coliform and Mercury. While this basin does have elevated dissolved oxygen levels, they are not attributed to elevated nitrogen of phosphorus values. Therefore, net improvement water quality improvement is not required. 4 The proposed design will employ conventional prescriptive wet detention treatment criteria. The wet detention treatment system captures the first one-inch of runoff from the contributing basin. This Required Water Quality Treatment Volume (WQTV) is then stacked between the seasonal high water level (SHWL)/Control Elevation and the Overflow Elevation. This type of system utilizes a bleed down orifice (or weir) to drain the treatment volume in 120-hours (5 days) with no more than one-half the total volume being discharged within the first 60-hours (2.5 days). Refer to Table 3.1a for the required water quality treatment volume, volume provided, weir size, and treatment stage. Refer to Appendix O for additional information. Table 3.1a – Wet Detention Treatment Basin Required Provided Treatment Orifice Size Treatment Area WQTV WQTV System (in) Stage (ft.) (Acres) (ac-ft.) (ac-ft.) 0.75” Pond 100 2.46 0.205 0.221 (Circular 32.90 Orifice) 3.2 Stormwater Attenuation 3.2.1 Southern Discharge (E. Columbus Drive) For the contributing drainage basin historically draining south to E. Columbus Drive, attenuation is provided such that the post-development 25-yr/24-hr discharge rates are equal to or less than the pre-development 25-yr/24-hr runoff within the