| | | | | | | | | | Item 10.
COMMITTEE MEMORANDUM | | | |
| | | | | | | | | TO: | Sustainability Resiliency Committee Meeting |
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| FROM:
| Jimmy L. Morales, City Manager
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| | DATE: | June 26, 2019
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| | SUBJECT: | A DISCUSSION REGARDING A BIOSWALE PILOT PROJECT FOR 59TH STREET WEST OF ALTON ROAD. |
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| | | | | | | | RESPONSIBLE DEPARTMENT:
Public Works |
| | | | | | | | LEGISLATIVE TRACKING:
ITEM C4 J - JUNE 5, 2019 Commission Meeting |
| | | | | | | | SPONSORED:
Commissioner John Elizabeth Aleman |
| | | | | | | | BACKGROUND:
The City of Miami Beach is investigating the use of stormwater infrastructure best management practices to address water quality issues for Biscayne Bay, which is designated an Outstanding Florida Water by the Florida Department of Environmental Protection. In addition, the City is looking for ways to integrate the City’s green areas with the current stormwater program. One possible option to address both water quality and the stormwater integration green space is the use of bioswales. As an initial investigation into bioswales, the City is seeking to implement a pilot project as means to test the efficacy and value of this technology to provide water quality improvements and attenuation of the runoff from developed areas of the City.
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| | | | | | | | Analysis
PROJECT DESCRIPTION
The La Gorce neighborhood, West 59th Street, was targeted for this pilot project due historical flooding of low-lying homes along the street. The bioswale pilot project is located within the West 59th Street right-of-way, between Alton Road and Biscayne Bay. The runoff from the existing roads and sidewalks will be managed by a series of proposed bioswales.
For the purposes of this study, the design target is to manage the first 1.5-inches of the storm events within a typical year. Runoff from the impervious road and sidewalks will be directed to multiple depressed storage areas (bioswales), where the design volume runoff will be captured and not discharged to the stormwater collection system of underground pipes, unless the storm event is larger than the 1.5-inch design volume.
BIOSWALE OBJECTIVES
Bioswales can improve stormwater runoff water quality by allowing solids and other pollutants to settle out of the water naturally in the bioswale depressions and the engineered soils beneath the surface of the basin, rather than passing into storm sewers and eventually the waterways and ecosystems.
The objective of this evaluation will focus on quantifying the benefits of using this approach and identifying feasible design alternatives to provide the water quality and volume attenuation benefits for the target demonstration site. A bioswale stormwater best management practice was selected by the City to be demonstrated at this site, since it will provide on-site retention of the runoff from lawns, driveways and roads within a residential neighborhood that is ripe for other infrastructure improvements.
BENEFITS
• Effective removal of suspended solids, nutrients (nitrogen and phosphorus) and other pollutants from stormwater before it enters the bay;
• Allows stormwater to infiltrate into the ground and replenishes the fresh water lens beneath Miami Beach – this supports robust green spaces;
• Captures the first flush (1.5-inches) of runoff from every rain event to remove contaminants; and
• Beautifies the area with attractive landscape and utilizes a variety of native plants to minimize maintenance requirements.
LIMITATIONS
• Bioswales are not intended to solve flooding in low lying areas;
• Periodic maintenance is required, for example the mulch will need to be replenished or replaced to maintain its functionality;
• Only the first 1.5 inches of large rain events will be captured – excess water will bypass the bioswale due to limited capacity; however, this adequately treats contaminated runoff per county and state regulations.
• Potential loss of parking when bioswales are located in swale areas currently used by property owners for parking.
• Costs of bioswales can be expensive. For this pilot project, the overall estimate cost is approximately $850,000.
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| | | | | | | | UPDATE:
Wade Trim is being considered for a pilot program on 59th Street, West of Alton Road. They have provided the City a rendering, and a planning-level cost estimate in the amount of $850,000. This amount would include the design and construction of three different types of bioswales to be installed within close proximity to each other to allow the Administration to monitor and measure their relative efficacy, while allowing residents to observe bioswales in a neighborhood-built residential context.
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| | | | | | | | CONCLUSION:
The following is presented to the members of the SRC for discussion and further direction. | | |
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