Miami needs $5 billion to fight flooding

Miami’s new stormwater master plan prioritizes $600 million in near-term infrastructure improvements and anticipates over $5 billion will be needed to shore up the city against flooding and achieve long-term resiliency goals.

After extensive research evaluating areas subject to extreme flooding, the City of Miami recently updated its stormwater master plan. The new, comprehensive strategy considered changing climate patterns and anticipated sea level rise to identify improvements to drainage systems and $600 million in projects needed in the coming years to address flooding.

The city’s previous stormwater plan, written in 1986 and last revised in 2012, was outdated due to changes in land use, regulatory requirements and projected impacts from sea level rise and rainfall models. As such, the city awarded a contract to CDM Smith in April 2018 to develop an updated master plan that was released in April 2022.

On March 14, Miami commissioners unanimously approved the new plan that provides the city with a detailed, dynamic stormwater model to stimulate predicted rainfall and flooding and measure the effects of sea level rise and storm surge on the existing and proposed stormwater management system. The model can be modified as new projects come online or conditions change.

The report recommended infrastructure improvements that are separated into 49 sub-basins and prioritized into four groups. The plan’s total cost is $5.39 billion to achieve the 10-year level of service goals and $3.82 billion to reach the 5-year goals.

After the plan was released, city staff conducted a series of community engagements to establish priorities for using immediate funding available through Miami Forever Bonds and other sources.

The meetings culminated with 24 neighborhood projects, at an estimated cost of $600 million, classified as immediate priorities based on historic flooding complaints, damage claims and significant flooding that poses a risk to residents.

The prioritized flood-prone areas include the Melrose neighborhood in commission District One, the Brickell Business District, Morningside and Edgewater neighborhoods in District Two, the Latin Quarter, South Shenandoah and Riverside/Jose Marti Park neighborhoods in District Three, Coral Gate and La Pastorita neighborhoods in District Four and the South Shorecrest neighborhood and Northeast 84th Street in District Five.

Infrastructure improvements in those areas include upsized stormwater inlets and pipes, seawall replacement, living shorelines, exfiltration trenches, gravity drainage wells and pump stations with outfall to Biscayne Bay and the Miami River.

The analysis of current flooding conditions showed that the drainage system issues are caused by a mixture of environmental and infrastructure variables. Miami’s high groundwater table and high number of impervious areas combined relatively flat terrain limit storage area.

The report states the most cost-effective stormwater management components for the Miami area are exfiltration systems due to the high flow capacity of the Biscayne Aquifer. These systems collect, store, infiltrate, treat and convey stormwater in the city’s available rights-of ways and easements for the lowest cost. Benefits of exfiltration systems include flood mitigation, water quality treatment credits and aquifer recharge for reduction of saltwater intrusion and protection of groundwater supplies.

The plan also highlights green infrastructure as a key component to resiliency. The report states that the synergist effect of the installation of many green infrastructure systems spread throughout the city can become helpful for chronic flooding areas and allow each resident to participate in the flood solutions on their own sites.

Near-term resiliency planning actions on the 20- to 50-year horizon include structural and nonstructural components like updating building code strategies, evaluating minimum elevations to consider future sea level rise, securing dedicated financing sources, public-public partnerships with Miami-Dade County, the Florida Department of Transportation and the South Florida Water Management District, launching a public awareness campaign, preserving and creating natural coastal wetlands to block surge flow and raising of critical infrastructure to an appropriate resiliency height.

Long-term resiliency planning includes future adaptation considerations like raising the lowest-lying elevations in the city, as well as in Miami-Dade and Broward counties, in a phased reconstruction. The lowest-lying areas would eventually be excavated to create large, dedicated storage areas for stormwater and potentially providing fill for some of the remaining areas.

Another long-term proposal is co-existing with water and modifying the basic design of the city to adapt to future sea level rise and flooding. These considerations include building code changes and exploring elevated pile roadway networks, elevated houses, floating neighborhoods and platform communities in low-lying areas over the created water catchments, sealing underground utilities and converting low-lying streets to an interconnected canal system for transportation and flood control.