City of Naples, Florida, Sustainable Stormwater Infrastructure Improvements for Improved Coastal Resiliency

The city of Naples discharges stormwater through large pipes (18–48” diameter), supported by timber structures, which cross the beach and release the stormwater into the Gulf of Mexico during high frequency rainfall events. Periodic beach nourishment results in a dynamic shoreline which often blocks the outfall pipes’ flow due to sand build up, causing upstream flooding of the adjacent beach road which has elevations generally less than 4 ft MSL. This requires the upstream swales and roads to stage (flood) to open the blocked or tidally flooded pipelines for stormwater to discharge to the gulf. In addition, these outfalls often become a petri dish for bacteria such as E. coli and enterococci and pre-date current, regulatory oversight prohibiting such discharges. The authors designed a functional and constructible stormwater infrastructure improvement project to reduce flooding (including sea level rise) and storm damage (for coastal resiliency) during high frequency events (e.g. <25-yr return period). The design consolidates the stormwater flow associated with five beach outfalls and conveys it to a pump station with water quality treatment and discharge through two directionally drilled pipelines a distance of 1,100 ft offshore. The beach outfalls will be removed from the sandy beach. Additionally, an overflow system will convey stormwater during extreme storm events when peak discharge volumes exceed the maximum capacity of the pump station. The design is a low impact and sustainable system to alleviate flooding and water quality issues on Naples Beach which was directly impacted by Hurricane Irma (Category 3) in September 2017.