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07-27-24 SW Presentation - Attachment AStormwater & Resiliency Town Hall Meeting July 27, 2024 esiIiency The ability of city systems to adapt and thrive in the face of acute shocks and chronic stressors. Stressors on Atlantic Beach ➢ Acute • Extreme Rainfall Events • Extreme Heat Events • Infrastructure Failure • High Winds ➢ Chronic • Sea Level Rise • High Tide Flooding • Heavy Rainfall • Coastal Erosion • Urban Heat Island Effect • Aging Infrastructure City of Jax Goals for a Resilient City > Proactively adapt > Foster healthy communities and environments > Expand opportunities ➢ Build for the future Atlantic Beach Resiliency Action Coastal Vulnerability Assessment • Identified critical infrastructure exposure and vulnerability • Currently being updated with new information Adaptation Plan • Actions to be taken to minimize vulnerability • Living document updated as new information is received Resiliency Assessment • All capital projects assessed in the context of resiliency Trends > Extreme Rain Events —1.5-2 times increase expected by 2070 > High Tide Flooding Days — 40-60 more days annually anticipated by 2050 > Increase in Impervious Area — Trend is towards max allowable lot coverage > Tougher Stormwater Requirements — New rules require: • Increased nutrient reduction requirements • 80% Phosphorus • 45% Nitrogen • Increased operations and maintenance requirements 061 045 008 0.15 Io. 2 -0.15 -0.30 -0.45 Trends 8720218 Mayport, Florida 2.62 • - 025 min r Linen Relative Sta Level Trend —Upper 95% Confidence interval — Lower 95% Confidence Interval _ Monthly mean sea level with the average seasonal cycle removed 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 • 2600 2010 2020 Storm Sewer System Overview ➢City served by a series of pipes, ditches and canals ➢Mostly constructed prior to modern standards ➢Many improvement projects are planned or underway ➢Water quality treatment is not provided in most of the system ➢Design goal level of service for flood protection: • Residential streets should be passable with water not exceeding the crown of the road during a 5 - year flood event (6.1 inches in 24 hours). Drainage Basins Sherman Creek Sherman Canal Legend Sherman Creek Watershed Puckett Creek. Watershed Sherman Canal Watershed Hopkins Creek Watershed Intracoastal UVatershed City Limits Hopkins Creek Sherman Canal Water Levels Hurricane Irma - 2017 City Hall Water Level 6.4 FT ABCC Mayport Rd Puckett Creek Water Level 5 FT 2.5 Miles For reference, Howell Park at Pine St is at elevation 5 FT Community Development Board (CDB) Recommendations Section 24-68(b)(1) -Improvements that exceed 50% of the market value triggers onsite stormwater ➢ Recommendation: Remove trigger (as long as property remains at 45% lot coverage) > Discussion: • Intent was to require tear -downs to implement onsite storage • 50% was utilized as the threshold to be in line with other requirements that properties be brought into compliance with all codes when the 50% threshold is exceeded • A different threshold could be considered • Threshold could be eliminated, resulting in grandfathering all existing impervious area CDB Recommendations Section 24-68(b)(3) - One time exemption from Onsite Stormwater Requirements ➢ Recommendation: Remove this trigger for willful demolition or remodel. Allow for issues related to natural disasters ➢ Discussion: • Intent was to allow for complete remodel of older homes (exceeding the 50% threshold) that didn't result in an increase in impervious area to be exempt • If removed, major remodels will be required to implement onsite stormwater • In these cases, onsite stormwater is difficult to implement without impacting mature landscape/trees • "One time" could be removed from exemption language • Allowances for rebuilding after natural disasters already contained in Section 24-85(c)(4) CDB Recommendations Section 24-68(b)(2) -Increase in impervious surfaces by 250 square feet triggers onsite stormwater for the square feet added ➢ Recommendation: Remove trigger (as long as property remains at 45% lot coverage) ➢ Discussion: • The intent was to allow for walkways and other small improvements to be completed without the burden of creating onsite storage • Removing the trigger may result in significant increase in stormwater runoff as properties below the 45% maximum lot coverage expand without storage • The trigger was formerly 400 square feet; that could be reinstated. • An analysis could be completed to objectively determine appropriate trigger CDB Recommendations Section 24-17 -Definitions - The water surface area of swimming pools shall be calculated as fifty (50) percent impervious surface > Recommendation: Keep this calculation > Discussion: • Many cities consider pools as impervious, while others consider pools pervious • 50 percent impervious was a compromise based on arguments that pools generally have some degree of freeboard and retain some stormwater water • Difficult to calculate & enforce freeboard requirements • Stormwater that does fill a pool must eventually be pumped out CDB Recommendations Onsite Stormwater Retention - Tailor stormwater retention according to the hydrology of specific neighborhoods ➢Recommendation: Have City staff research and define hydrology based on topography and geographic areas. > Discussion: • Soil types and depth to the groundwater table vary across the city • Onsite storage requirements currently account for depth to the groundwater table; the deeper the groundwater table, the more soil storage is credited • This recommendation is probably best analyzed during completion of the next Stormwater Master Plan update CDB Recommendations Pervious Pavers ➢ Recommendation: Allow to be treated as permeable as determined by the manufactures specifications and ensure they are installed correctly ➢ Discussion: • Open grid pavers (turf block) are provided 50% credit • Pervious pavers require maintenance (per most manufacturers' specifications) to maintain permeability —vacuuming, etc. • Staff has observed older pervious pavers that don't percolate water well • Open grid pavers and tabbed pavers (pavers with visible joints between the blocks) appear to work better over time than permeable type pavers where water soaks through the paver • Could allow full or partial pervious credit for various types of pavers (25% credit was considered at one time) Paver Types Pervious Pavers—Tabbed Blocks Open Grid Pavers — Turf Block Permeable Pavers — No Tabs on Blocks Paver Performance • -•‘ Pervious Pavers — 7 years old 1.2 inches of rain in 45 minutes Pervious Pavers — 14 years old 1.2 inches of rain in 45 minutes Permeable Pavers —10 years old 0.7 inches of rain in 2 hours Paver Performance Open Grid Pavers — 10 years old 0.7 inches of rain in 2 hours 1 1 1 1 1 I 1111 11111 1 r��iIIJ _Ys Pervious Concrete — 8 years old 0.7 inches of rain in 2 hours Pervious Pavers — >14 years old 1.4 inches of rain in 1.25 hours CDB Recommendations Artificial Turf > Recommendation: Allow to be treated as permeable as determined by the manufacturers' specifications and ensure they are installed correctly (need to weigh the environmental aspects) > Discussion: • Currently artificial turf is considered pervious if it is demonstrated to Public Works personnel that it is pervious • Some cities have banned artificial turf due to localized heat effects, potential for water pollution, runoff potential, etc. • Some cities, like Orlando, consider it impervious area • Some artificial turfs percolate better than others • Some types of artificial turf do not percolate water well • Similar to pavers, maintenance is required — brushing, debris removal and occasional rinsing to maintain appearance and drainage Pervious Artificial Turf Types Woven Backing Solid Backing - Hole -Punched for Drainage Final Thoughts > Atlantic Beach is flat, surrounded by water and has a high groundwater table, making it difficult to get rid of stormwater runoff in a cost-effective, efficient and permittable manner > Small changes in runoff can have measurable cumulative impacts over time on the stormwater drainage system > The 2012 Stormwater Master Plan Update concluded that by far, the most cost-effective means of controlling stormwater runoff is at its source — onsite storage > The City's Stormwater Utility Program generates about $865,000/year. Rates have not changed in 20 years and funds are barely adequate to cover maintenance > The 2024 Stormwater Master Plan Update should include an objective evaluation of CDB concerns and recommendations, revisit onsite stormwater calculations to make sure we have it right and consider the impacts of climate change