The Florida Department of Transportation (FDOT), District One, conducted a Project Development and Environment (PD&E) study for proposed improvements, including consideration of a single lane roundabout at the intersection of State Road (SR) 70 and SR 72 west of Arcadia in DeSoto County, Florida. This project involves raising and realigning SR 72 for approximately 0.85 miles between County Road (CR) 661 and SR 70. The SR 70 alignment will also be raised above historic flood levels and will require roughly a 1.05 mile of raising and reconstruction of SR 70 from CR 661 to the Peace River Bridge. A roundabout is proposed in lieu of the stop-controlled intersection. The proposed project would improve the overall safety and operations of both roadway facilities by mitigating the risk of flood damage to the road, reducing unplanned road closures due to severe flooding, and improving the overall safety of the intersection. Multi-modal improvements, including a shared use path, are proposed as additional safety improvements.
The purpose of this location hydraulic analysis is to evaluate floodplain encroachments and discuss the proposed measures to avoid or minimize floodplain impacts associated with the project. Proposed improvements are anticipated to mimic existing drainage patterns. A dry retention pond (wide swale) is proposed north of SR 70 between the roundabout and the Peace River relief bridge to provide stormwater management for SR 72 and portions of SR 70 and is discussed in the Conceptual Drainage Report (under separate cover). The project is within the Southwest Florida Water Management District (SWFWMD) and will require an individual Environmental Resource Permit (ERP).
The Federal Emergency Management Agency (FEMA) effective Flood Insurance Rate Maps (FIRMs), dated November 6, 2013, depict Zone AE, A, and X floodplain limits within the project proximity. The Zone AE floodplains, which are areas that have a 1% chance of annual flooding, are consistent with the Peace River and its overbank area. This riverine floodplain encroaches into the SR 72 and S.R 70 right-of-way and has a Base Flood Elevation (BFE) of 25.0 feet and 26.0 feet. The Zone A floodplains, which are areas that have a 1% annual chance of flooding, but do not have an established BFE are located along the western portion of SR 72 within the project limits. Improvements at the Peace River bridge and relief bridge along SR 70 are discussed in the Bridge Hydraulic Technical Memorandum (under separate cover). The project area is within an open basin where runoff flows via sheet flow to roadside ditches and through existing cross drains in a general southeast direction towards the Peace River. There are four cross drains which convey flow from the north side of SR 72 to the south side, towards the Peace River. Contributing areas were delineated by utilizing CatchmentSIM (CSIM) software and available LiDAR, reviewing existing permits and plans, and field reconnaissance. Interconnected Channel and Pond Routing (ICPR) Model software was used to determine peak flows and peak stages at the existing cross drains. Actual rainfall data from Hurricane Irma (2017) and Hurricane Ian (2022) was used to calibrate the model results.
During the design phase, the proposed cross drain facilities will be prepared in accordance with the FDOT Drainage Manual (Topic No. 625-040-002). Proposed conceptual modeling was performed to estimate proposed cross drain sizes. EX-0 remained unchanged and EX-3 is proposed to be removed (rerouted to CD-2). CD-1 size was increased to provide sufficient capacity for a wildlife crossing. CD-2 was upsized to maintain the upstream stage within the wetland. It is expected that the proposed improvements will include extension, modification, or replacement of existing drainage structures, which will perform hydraulically in a manner equal to or greater than the existing structures, and backwater surface elevations are not expected to increase. Thus, there will be no significant adverse impacts on natural and beneficial floodplain values. As a result, there will be no significant change in flood risk, and there will not be a significant change in the potential for interruption or termination of emergency service or emergency evacuation routes. Therefore, it has been determined that this encroachment is not significant.
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