Master Plan Development - City of Boca Raton

City of Boca Raton Stormwater Management Master PlanExisting Levels of Services5. Existing Levels of ServiceA. Permitted Finished Floor Elevations and Minimum Road Protection LevelsSFWMD permit files provided information on minimum finished floor elevations and minimumroad crown elevations. In the case of some permit modification applications, where no specificinformation was provided on these values, it was assumed that the values established in theoriginal permit for the area were still in effect. The minimum finished floor elevation for aproject is typically set above the calculated maximum flood stage resulting from a 100-year/3-dayrainfall event. In some cases, the minimum finished floor may be set according to FEMA floodelevations, or in relation to other nearby finished floor elevations or road crown elevations.Figure 11 displays the minimum finished floor elevations for the permitted areas within the City.The information is overlaid atop the GIS coverage of the FEMA flood zones provided by theCity. It’s worth mention that FEMA is in the process of updating their flood insurance rate mapsto reflect more current information. Preliminary reviews have suggested that these changes couldhave a significant economic impact on the communities being updated (the entire City, less the C-15 drainage basin). It is recommended that the City keep informed about the progress of the mapupdates and review any preliminary documents made available.Minimum road crown elevations are designed to be at or above the peak flood elevation resultingfrom a specified design rainfall event, when established according to SFWMD regulations. Therainfall event is considered to be the “level of protection” or “level of service” for the roadway.SFWMD has increased its minimum level of protection for roadways to the 5-year/1-day event.As stated earlier, the design storm event specified to meet the City’s level of service for roadwaysis the 3-year/1-day event. The City’s LOS requirement pertains to areas of new development orsignificant re-development, where the adjustment of a minimum road elevation would not createnegative impacts within or adjacent to the project. When minimum road elevations areestablished using more intense rainfall events, the road provides a higher level of service. Majorroadways are typically designed to provide a higher level of protection than local orneighborhood roads. For example, FDOT and Palm Beach County roadways may provide levelsof protection from a 10-year/1-day rainfall event. Figure 12 is a map of the design rainfall eventsfor which the minimum road elevation was provided in the SFWMD permits. Many areas withinthe City were developed prior to permitting requirements and the level of service on the roadwaysin those areas is not documented.While the specific rainfall amount for the permitted design storm was not recorded during permitfile review, it could be added to the database at a later date. Design rainfall amounts (typicallyobtained from the SFWMD Vol. IV Permit Manual) have changed over time. They are alsosubject to interpretation, as the selected value is read off rainfall curves shown over an outline ofthe South Florida area. This presents a complication to directly comparing established levels ofroadway protection. In addition, while rainfall volume increases with return frequency (a 100-year event has a greater rainfall volume than a 3-year event), intensity decreases with stormL/bocaswmp/a6016.01/InterimReport 11-27-07/r02Page 15MOCK•ROOS