As a result of damaging storms such as Hurricane Matthew in 2016 and ongoing issues related to sea level rise, flooding events are occurring more frequently along the low-lying coastal areas of the City of St. Augustine.
Tidal flooding is the most common type of flood event, characterized by spring or king tide events that cause tide waters to enter urban areas even without storm events. To address tidally-influenced nuisance flooding within St. Augustine, the City desired to implement tidal and stormwater backflow prevention on vulnerable stormwater outfalls within the Davis Shores subdivision, a particularly vulnerable residential area located on Anastasia Island.
Geosyntec's Scope of Services
Geosyntec performed a rapid assessment of eight stormwater outfalls within the Davis Shores subdivision affected by tidal flooding. Geosyntec worked with the city's in-house stormwater maintenance crews to establish suitability of in-pipe of end-of-pipe backflow prevention retrofits using TideFlex and WaStop backflow prevention devices. Measurements and observations were taken at each outfall and upstream storm sewer system to determine:
- Issues that would affect installation
- Remediation and maintenance needs before retrofitting
- Long-term maintenance and cleaning requirements
- Accessibility constraints to install and maintain
- Installation personnel requirements (in-house city maintenance staff or term contractor)
Outfall fact sheets were developed for each outfall to enable decision making as to the appropriate installation methodology, backflow preventer type, and recommended retrofit location (end-of-pipe or upstream improvement).
Geosyntec's work helped the city to apply for and receive a St. Johns River Water Management District Cost Share grant for the installation costs. The backflow prevention devices were installed primarily by the city's internal maintenance staff and have successfully reduced nuisance flooding.