In the May Water Wednesday webinar Stormwater 101: Understanding Drainage, Ponds, and How Florida Manages Rainwater, Dr. Eban Bean, Associate Professor and Extension Specialist of Urban Water Resources Engineering at the University of Florida explains how Florida manages rainfall runoff, why stormwater ponds are common throughout the state, and how everyday landscape decisions can affect water quality.
The Urban Water Balance Shift
Development changes the natural water cycle by increasing impervious surfaces such as roads, rooftops, and parking lots. As less water infiltrates into the soil, more rainfall becomes stormwater runoff (percentages are relative).
- Natural Landscapes: In undeveloped areas, roughly 50% of rainfall infiltrates the ground, 40% returns to the atmosphere via evapotranspiration, and only 10% becomes runoff.
- Residential Landscapes: In neighborhoods with 30% to 50% impervious surfaces, runoff triples to 30%.
- Ultra-Urban Landscapes: In downtown centers, runoff increases to 55%, while infiltration drops to 15%.
- “Flashy” Systems: Urbanization creates “flashier” systems where the volume of runoff is higher, the peak flow rate is greater, and the time between peak rainfall and peak runoff is much shorter.
Florida’s Pollutant and Rainfall Dynamics
Unlike many states where sediment is the primary concern, Florida’s main pollutants are nutrients (nitrogen and phosphorus). These nutrients come from over-fertilized lawns, roadways (oils, brake dust), and pets. Interestingly, it is not large hurricanes that cause the most nutrient issues; 85% to 90% of nutrients in runoff are generated by small, frequent afternoon thunderstorms of one inch of rain or less.
Infrastructure: Conveyance and Collection
A stormwater system involves moving water from the watershed (where it is generated) to Best Management Practices (BMPs) for treatment.
Key components of these systems include:
- Curb and Gutter: Roads are typically “crowned” to move water to the edges, where curbs (the vertical part) and gutters (the bottom part) funnel water to inlets.
- Inlets and Grates: These openings transition water into the pipe network. Grates act as screens to keep large debris out of the system.
- Pipes: Common materials include corrugated plastic, metal, and concrete. Smooth-wall pipes are preferred to prevent water from getting trapped behind ridges.
- Swales: Grassy channels that both move water and allow for infiltration and filtration.
The webinar also discussed several common stormwater BMPs used throughout Florida. There are over 76,000 stormwater ponds statewide.
- Detention: These “flood control” systems capture runoff and release it slowly to reduce peak flow rates, though they provide minimal water quality benefits.
- Retention: These systems (wet or dry) retain a volume of water to allow it to soak into the ground or evaporate. Wet retention ponds are the most common in Florida and maintain a permanent pool by intersecting the groundwater table.
- Exfiltration: Underground systems, often under parking lots, function like septic drain fields to allow water to seep into the subsurface.
Green Infrastructure and Innovative Solutions
- Permeable Pavements: These materials look like “Rice Krispie treats” because they lack fine particles, creating voids that allow water to drain directly through the surface.
- Bio-retention and Bioswales: Landscaped areas with engineered soil and vegetation that filter pollutants from runoff.
- Cisterns: Large tanks that capture roof runoff for reuse, such as landscape irrigation, which helps recover storage capacity before the next storm.
Highlights from the Q&A
What are the risks of sealing permeable pavers or porous pavement?
While sealing cracks in standard pavement is a common maintenance task, sealing permeable pavers, porous concrete, or porous asphalt is highly risky. These surfaces are specifically designed with interconnected voids to allow water to drain through them; applying a sealer fills these voids and effectively destroys their drainage function. Dr. Bean noted that this often occurs when a property changes hands and the new owner is not informed that their pavement is specialized.
Why not use artificial grass to prevent nutrient runoff from lawns?
There are several factors to consider before choosing artificial turf. First, it can become significantly hot due to a “heat absorption effect”. Furthermore, unless it is installed with professional-grade drainage, it often creates an impervious layer because the base is typically made of “crushed fines” that compact and prevent water from soaking into the ground. Finally, it is not maintenance-free, as weeds will eventually find a way to grow through it.
How is stormwater managed in jurisdictions that require all runoff to be retained on-site?
In residential developments, this is typically achieved through dry retention basins or wet retention ponds located within the boundaries of the community. However, retaining everything on-site is difficult in areas with poor soils or high water tables. Dr. Bean mentioned that new regulations may soon allow developers to purchase off-site treatment credits if the specific conditions of a property make on-site infiltration unfeasible.
How can stormwater ponds be made to look less “sterile” and more environmentally friendly?
Dr. Bean recommends the use of a littoral zone, which is a ring of vegetation growing out of the water around the pond’s rim. This vegetation is functional as well as aesthetic; it absorbs wave energy to prevent the pond banks from eroding and helps filter nutrients from the landscape. He also suggested maintaining a 10-foot buffer zone around the pond where no fertilizer is applied. He emphasized that ponds should be managed holistically, much like a fish tank, by balancing nutrient cycles rather than just treating symptoms like algae,.
What is the difference between using concrete and asphalt for roadways?
Concrete is a “rigid” pavement system that is more expensive and intensive to install but has a much longer lifespan. This makes it ideal for interstates where shutting down lanes for frequent repairs is not an option. Asphalt is a “flexible” system that is cheaper upfront but breaks down more quickly. Consequently, asphalt is more commonly used for local, lower-traffic roads where maintenance is easier to manage.
Additional Resources
Find more information on Green Stormwater Infrastructure.
Watch the Recording
If you missed the webinar or would like to revisit the content, you can watch the full recording here.
Join Us for the Next Webinar: Hurricane Preparedness
The next session in the series will be held on June 17, Hurricane Preparedness: A Guide for New Florida Residents. We cover evacuation zones, alerts, emergency kits, home preparation, wind mitigation basics, generator safety, and common hazards during post-storm recovery. Register via Zoom.
Whether you are new to Florida or have lived here for years, this webinar will provide a helpful overview of how Florida’s water resources work. More information please visit UF/IFAS Extension Water Resources Program.
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