At its March 17, 2021 meeting, the City Commission approved a referral to the Land Use and Sustainability Committee (LUSC) to discuss litter getting into the City's stormwater drains and potential action if deemed necessary.

The referral originated from a Biscayne Bay Health seminar that took place on February 19, 2021.  During this seminar, discussions identifying the need for Miami-Dade County and the Cities of Aventura, Miami, and Miami Beach to take on a new set of goals were had, including the benefit of coordinating stormwater drains. 

One of the main concerns raised at the seminar was the health of the Bay, and how it is believed to contain excessive nutrients, and how stormwater is a large conveyor of nutrients from natural debris that is composting in the stormwater systems. When it rains, the nutrients from the decomposed leaves and grass clippings flushes out to the Bay. Currently, the City of Aventura and Miami are implementing storm inlet grates with expanded street sweeping, said to be effective in keeping debris out of the stormwater system, thus reducing maintenance costs and improving water quality.

At the September 14, 2021 meeting of the LUSC, Commissioner Samuelian introduced the item, stating the community wanted to ensure the City was doing its best to protect the Bay.   Public Works staff proceeded with discussing a recent pilot project to test different types of grates that proved to be unsuccessful. There had been many service requests due to litter accumulation at the grates despite being serviced daily. The grates were also found to cause flooding.

The City’s existing stormwater treatment systems and pump stations include various stages of treatment that capture litter and debris.  Additionally, the new generation stormwater treatment systems being implemented in projects such as West Avenue and First Street, also include wells to sequester contaminants.

Since previous experience using grates had resulted in additional flooding without significant benefits beyond what is already provided, the Administration recommended against using stormwater inlet grates. At the end of the discussion the LUSC agreed with the stated by Public Works conclusions and made a motion to conclude the item.

At its January 20, 2022 meeting, the City Commission approved a referral to the LUSC, to discuss storm drain grates once again. Staff presented at the February, 2022 LUSC meeting. Staff noted they will continue evaluating alternatives for further improving debris removal from the stormwater system. Staff is presenting an update to this evaluation herein.

The City of Miami Beach has tested stormwater grates in the past.  During a pilot program, the City installed inlet grates along Ocean Drive, from 5th Street to 12th Street.  However, the program was unsuccessful.  

During rain events, the flowing debris would get caught in grates, causing the drains to clog.  These clogs would then create flooding within the streets and sidewalk cafes.  The flooding was predominantly present at the locations where the grates were installed.  The City received numerous phone calls, service requests, and other complaints regarding the ineffectiveness of the grates during the time they were installed.  Attempts were made to have the grates’ performance from the pilot program optimized by the vendor, however, the clogging and flooding persisted.   

Since litter and debris would be caught within the stormwater system, prior to discharge by the existing water quality treatment devices (inlet sumps, bar screens, vortex units etc.), City staff determined it was best to have the grates removed in order to reduce flooding.

Staff discussed their experience with City of Miami’s staff who noted they also did a pilot to install 20 storm inlet grates. Their experience was similar, in that the grates got clogged with street debris, leaves, etc, so frequent street sweeping was crucial to their functionality.

Furthermore, City staff has continued to research and evaluate options for large debris capture in the City’s stormwater system. Exhibit 1 presents the comparison of three alternatives, which included the following:

1.    Stormwater grates at every inlet,

2.    Consolidated debris capture at bar racks,

3.    Consolidated debris capture at outfall filtration nets (new strategy recently implemented by Australian municipality).

After carefully assessing the pros and cons of these options, the continued use and further implementation of bar racks for consolidated debris capture is still recommended. This is the City’s current approach, which provides the same level of filtration as the inlet grates, however, with a consolidated location, reduces the maintenance requirements and costs. Furthermore, City operations staff is already set up and familiar with maintaining these bar racks system. These systems have been in use at the City of Miami Beach for decades; they have low visual impact and are designed to not impact the stormwater flow, therefore do not exacerbate flooding. Staff recommends the continued implementation of bar racks for large debris removal from the City’s stormwater system.

It is important to note that the City’s existing pump stations include various stages of treatment that capture litter and debris.  Additionally, the new generation stormwater treatment systems being implemented in projects such as West Avenue and First Street, also include wells to sequester contaminants. The City continues to evaluate further improvements to it stormwater management system. The recommended system for large debris removal continues to be the bar racks.