Currently, the City of Naples (“City”) Drainage Basin II (395 acres) system collects stormwater and discharges through ten (10) beach outfalls (18-48” diameter) located within the intertidal active beach. Periodic sand build-up and tidal elevations often prevent discharge causing upstream flooding of the adjacent roads which have elevations generally less than 4 ft MSL. The existing system pre-dates current, regulatory oversight, and due to the aging concrete pipes and stagnant untreated stormwater, the system discharges high levels of bacteria. The City has undertaken a proactive stormwater management program to improve water quality, flooding and coastal resiliency. Based on a combination of design, permitting and environmental considerations, there is significant (80%) improvements to water quality and reduction in flooding. The project consolidates, treats and conveys stormwater discharge through a pump station to an offshore pipeline. The project provides a subaqueous, Gulf outfall alternative and removes multiple existing beach outfalls. The goal of the Project was to design infrastructure improvement project to reduce flooding (including sea level rise) storm damage (for coastal resiliency) during high frequency events (e.g. <25-yr return period) and improve water quality. To address environmental concerns – flooding, beach erosion, beach access, sea turtle nesting habitat, water quality and aesthetics. RESILIENCE TO A CHANGING CLIMATE The existing stormwater sewer is a gravity flow system with beach outfalls affected by mid to high tidal phases, storm surge and sand build-up; each of which compromise or reduce the LOS and cause standing water. As sea level rise continues, inundation of the system by Gulf waters and related upstream flooding will increase due to reduced differential in elevation from the City’s upland drainage pipes and the Gulf water levels. Gulf discharge is thereby affected by the tides, storm surge and the increasing elevation of mean sea level. The pump stations allow the conveyance of greater flows and volumes than would be possible under normal gravity flow, thereby optimizing installed pipe capacities. This is a critical advantage for low-lying coastal communities subject to tidal influence. The design of the pump station included 0.9 ft of sea level rise for coastal resiliency. Overflow structures were designed to manage low frequency rainfall events associated with return period events exceeding a 10-yr/3-day event and including extreme storms such as a 25-yr return event. Despite the high uncertainty of climate change and sea level rise, it is important that the City develop infrastructure to have the resiliency needed to function adequately in the face of change. The opportunity exists with projects such as this one, where infrastructure is being modified or improved, to build this adaptation and resiliency into the normal infrastructure renewal cycle. This concept of “mainstreaming” adaptation by focusing on the most urgent effect of climate change and sea level rise allows resiliency to happen at very little adaption cost. Construction commenced January 2023 following Hurricane Ian.
