Miami Beach is a beautiful coastal community. Our sunkissed island is surrounded by the waters of the Atlantic Ocean and Biscayne Bay. Miami Beach is leading the way locally and nationally to reduce flood risk while protecting the environment.
Miami Beach is investing in public infrastructure and using the best available science to do so. The city is raising roads, installing stormwater treatment systems, raising sea walls, and creating higher elevation standards for new and substantial improvements. Our program delivers quality of life for residents and visitors today and provides for a sustainable and resilient tomorrow.
History of Drainage in Miami Beach
Before Miami Beach was urbanized, it drained towards the bay. In fact, back in the day, the west side of Miami Beach was largely mangrove swamps. When it rained water would drain from east to west - toward the mangrove wetlands.
When the City started getting developed, these swamps were infilled. However, the fill was placed to a lower elevation than the areas to the east. This preserved the natural drainage regime of the island.
Urbanization
As time passed and Miami Beach became a world wide destination, urban drainage systems were required to keep the streets and public areas dry. Then, as is the case today, drainage was not only a matter of convenience, but a necessity. Stagnant water poses a threat to the health and welfare of the City’s stakeholders. Passable streets allow emergency vehicles and first responders to quickly address dangerous situations. Thus, the first mechanical drainage systems were built.
Gravity Stormwater Outfall
Gravity drainage systems were the first built in Miami Beach. These systems convey water through a mechanism we are all familiar with - water flows downhill. This means that the entry elevation - where the inlet is located - is the highest point of the system. Water is then conveyed through the system until it reached the outfall - the pipe that discharges to the bay. This outfall has to be placed at a lower elevation than the upstream entry point so that the water can flow downhill.
Benefits of Gravity Outfall Systems
- No Carbon Emmision
- Minimal Maintenance
Limitations of Gravity Outfall Systems
- Limited Capacity
- Downstream Water Level Limits Flow
- Not Feasible During High Tides
Drainage Well Systems
As our City grew, more complex systems were constructed. It was a new era, the days where cities where built haphazardly were long gone. Even though decentralized development brought with it many good things, such as unique architecture, it did not always account for the overall needs of the entire city.
Engineers and Urban Planners were now thinking holistically. The drainage systems were designed to, not only dispose of the stormwater, but also treat it. They included bar screens, to keep trash from entering the bay, and pollution control units that trapped small particles. The engineers designed pumped systems to be able to move more water, and within the pump station, achieved additional treatment. Fats, oils, and grease floated at the top of the pump station, keeping them from entering the bay. The pump aerated the water, improving water quality by increasing the dissolved oxygen.
Benefits of Drainage Well Systems
- Adds Various Layers of Treatment
- Moves More Water than a Gravity System
Limitations of Drainage Well Systems
- Well capacity is Limited by the High Groundwater Table
- Can Cause Groundwater Mounding that leads to Flooding
- System is Not Effective During High Tide
Although the well systems were a significant improvement over the antiquated gravity systems, they were not without flaws. If these systems were over-pressurized, the water would mound, causing additional flooding and, at times, damaging the surrounding pavement.
Perhaps, the worst symptom was that the wells would exacerbate a phenomenon, known as "Sunny Day Flooding". A sunny day flood occurs when the groundwater or the tidal waters rise to a level that causes flooding on the streets. In order for sunny day flooding to occur, the elevation of the water would have to be higher than that of the street. While certain measures can mitigate sunny day flooding, such as back flow preventers on outfalls, these do not stop water from rising through the wells.
When the well systems were implemented the worked properly. However, as sea level began to rise sunny day flooding worsened. Eventually it was commonplace to see water rising out of wells in Miami Beach.
The flooding was particularly bad during king tides. The Astronomical High Tide, known colloquially as King Tides, occurs twice a year in April and October. It was during these months that sunny day floods posed the greatest threat.
Worse still, if the king tides were compounded by a storm, the result would lead to flooding that could endanger life and property.
Overtime it became evident that wells were not an effective means to dispose of stormwater in Miami Beach. Not only would they exacerbate sunny day flooding, but, overtime, their efficacy would be reduced by chronic sea level rise.
Pressurized Outfall System
After realizing that well systems were not a sustainable drainage solution, engineers began constructing pressurized outfall systems. These systems kept all the water quality treatment units upstream of the well but increased capacity by allowing the water to outfall to the bay.
Benefits of a Pressurized Outfall System
- Moved More Water than Well Systems and Gravity Systems
- Worked Under High Tide
Limitations of a Pressurized Outfall System
- Do Not Retain the First Flush of Runoff
- Do Not Replenish the Fresh Groundwater
A New Strategy
Quick Facts About Miami Beach
- Is one of the 30 permitted entities allowed to discharge stormwater in Miami-Dade County.
- Manages approximately 3.8% of the 8,000 outfalls in the county. The rest of the outfalls are owned by the county or other cities.
- Is implementing a new, pump-based stormwater treatment system that uses a multi-step filtering process, which helps prevent litter and debris from reaching Biscayne Bay
- Sweeps 177 miles of streets daily, removing more than 450,000 lbs. of sweeping material.
- Street sweeping removes more than 1,300 pounds of nitrogen and 840 pounds of phosphorous that would have otherwise reached Biscayne Bay
- Cleans 150% of the storm water system (catch basins, pipes, outfalls), each year.
Staying at the Cutting Edge of the Industry
To watch the entire discussion, with representatives from the City of Miami Beach, the City of Miami, and Miami-Dade County click the link below.
Next Generation Stormwater Treatment System
The City is currently implementing next generation stormwater treatment systems that combine the best attributes of wells and outfalls, while retaining all the upstream water quality elements. These systems are hybrid systems that include five stages of treatment, filtering the water and sequestering contaminants, prior to discharging the water to Biscayne Bay.
Five Stages of Treatment
- Bar Screens
- Pollution Control Structure
- Floatables Separation
- Aeration
- Shallow Drainage Well
Green Infrastructure
While the City of Miami Beach has come a long way in its drainage designs, its committed to keep pushing the limit on whats possible in terms of protecting the environment. To that end, the City is currently working to construct green infrastructure. Although these green solutions will not help with flooding, they will improve water quality. By passing the runoff through green spaces, the trees and shrubs will take up nutrients that can harm Biscayne Bay. Below are two green solutions the City is currently implementing.
Bioswales retain stormwater that ultimately helps to restore the natural hydrology. Bioswales also sequester nutrients from runoff, improving the quality of water being discharged to the bay.
Living shorelines restore the natural habitat of the bay, while protecting the City from the effect of storm surge. They also boast an aesthetic benefit that attracts residents and tourists to see a biologically diverse ecology.
For more information, please visit our websites below.