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2022-07-19 Miami City Commission handout, Tuesday, July 19, 2022
Re: Narrow Living Shorelines
By: Elvis Cruz 631 NE 57 Street Miami, Florida 33137 (305) 754-1420 ElvisCruz@mac.com
Several falsehoods are being promoted by mangrove enthusiasts with little regard for the
negative impact to the public's enjoyment of the public waterfront in public parks. The worst
example is the falsehood that a row of mangroves along a shoreline can stop hurricane storm
surge. Mangroves cannot defy the laws of physics, they cannot hold back a wall of water being
pushed by 100-plus mile an hour hurricane force winds. Here is the truth:
Storm surge: An April 13, 2022 Miami Herald article quoted three scientists on the
ineffectiveness a narrow shoreline planting of mangroves for decreasing storm surge.
https://www.miamiheraId.com/news/local/environment/article259496044.html
1. Peter Sheng, a University of Florida researcher who's studied the protective value of
mangroves in Florida, said they're an incredible tool when used correctly. In places like Cutler
Bay, huge swaths of mangroves provide a barrier between the 10-foot-plus waves from
hurricanes and populated areas. "If you have a narrow urban mangrove planter, it doesn't cut
it," he said. "Three meters of mangrove does nothing. It's a token for the look. If you want to
dissipate waves, you need at least 100 meters."
2. Rik Gijsman, a coastal engineer and researcher at the University of Twente in the
Netherlands... Gijsman said studies consistently show that to cut huge waves down to size takes
a lot of mangroves, an Everglades -sized amount of mangroves.
"Mangroves will never provide full safety for real storm surges," he said. "To really attenuate
the waves you need kilometers of them."
3. Yuepeng Li, a Florida International University researcher who's published multiple papers
attempting to quantify exactly how much protection mangroves offer...
...it takes about half a mile worth of mangroves to lop off even one foot of storm surge.
"Even one mile of mangroves, I don't think it will significantly decrease the surge," Li said.
Pictures from the State of Florida clearly show shoreline mangroves get destroyed by
hurricanes. See slide number 10: https://nmsfloridakeys.blob.core.windows.net/floridakeys-
prod/media/docs/20181016-fwcmangrove.pdf
The often quoted Nature Conservancy study on mangrove flood risk reduction benefits:
https://www.nature.org/content/dam/tnc/nature/en/documents/Mangrove Report digital FI
NAL.pdf On page 7: In hurricanes Charley and Wilma, mangroves reduced flood height only
4.2 to 9.4 centimeters per kilometer of mangrove forest width. That's an insignificant
reduction. On page 11: In Miami Dade there were only $1,400 in benefits per hectare of
mangroves. A hectare is 107,639 square feet, so that's $566 per acre. But what is the dollar
value of the public waterfront we would give up?
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Fish nursery: The larger the area mangroves cover over water, the more fish can be produced.
But living shoreline plans in Miami parks have shown the mangroves on land, so they can't
function as fish habitat. It is unlikely that DERM would give permission to plant mangroves in
the water, especially if it's too deep.
Rip rap placed in front of a seawall diminishes wave action and creates a living shoreline,
with many nooks and crannies. Also, concrete moldings can be applied to seawalls to incubate
oysters and other marine life. We need not block our parks' waterfront to help the
environment.
Oysters: Oysters are a viable solution, real science. Oysters clean the water. If you want to
filter water, you have to put the water filters in the water, not on the shoreline.
Fish kill misconception: Miami's fish kill of August 2020 was reported to have been caused by
five factors: 1. high water temperature, 2. leaking sewer mains under the bay, 3. Fertilizer, 4.
septic tanks, 5. storm sewers. The main source of pollution was from the Little River.
Note that nothing planted on the shoreline would change any of those factors.
The fish kill proved we already have a large fish population. 27,640 dead fish were
counted, representing 56 different species.
Alternative locations for planting mangroves: There are 2.88 miles of shoreline along the Julia
Tuttle causeway, 1 mile along the 79 St causeway, and several islands in the bay.
Carbon sequestration: The amount of carbon that would be sequestered by mangroves along
the shoreline in a City park is extremely insignificant, less than one car's production.
One acre of mangrove forest can store about 1,450 pounds of carbon per year.
(https://ocean.si.edu/ocean-life/plants-algae/mangroves )
Doing the math: Since there are 5.5 pounds of carbon in a gallon of gasoline, 1,450
pounds of carbon = 263 gallons of gasoline sequestered per acre per year. By comparison, the
average car uses 330 gallons of gasoline per year. (10,000 miles per year at 30 mpg. Many cars
are driven more miles and get less mileage.)
But the US burns 360 million gallons of gasoline per day. That's aside from jet fuel,
diesel, coal, natural gas and propane.
The proposed mangrove planters in Jose Marti Park would cover 0.071 acres. 0.071 acres x
1,450 pounds of carbon sequestered per acre each year = 102.95 pounds of carbon, which
equals only 19 gallons of gasoline sequestered per year.
Mangrove enthusiasts place little value on protecting the public's enjoyment, access and views
of the waterfront. Proposed living shorelines in Miami parks are ornamental environmentalism,
providing little benefit but a large detriment to the public's enjoyment. Good alternatives exist.
If anyone has any doubt about anything I've said or written, please challenge me. I would be
happy to meet and go over the scientific facts and impacts / benefits to the public.
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Coronavirus News Sports Business Personal Finance Public Notices
ENVIRONMEN T
Mangroves vs. seawalls? Mix may be `best of
both worlds' to take on South Florida sea rise
NY Al FX HARRI$
APRIL 13, 2022 6:00 AM
View of a mangrove restoration along the shoreline at Baywood Park in northeast
Miami, part of the county's former living shoreline projects on Biscayne Bay.
Living shoreline projects utilize a variety of materials such as wetland plants,
oyster shell, coir fiber logs, sand, wood and native rock. PEDRO PORTAL
Along most of the historic South Florida coast, mangroves were nature's
way of protecting the coast from waves and hurricanes. As development
Page 1 of 8
inched closer to the water, seawalls became the method of choice to
separate land and sea.
With two feet of sea level rise on the horizon by 2060, which is the right
choice for extending the life span of cities like Miami?
The science -- at least for pure flood control — suggests the man-made
answer wins out over nature's solution, with some caveats.
Peter Sheng, a University of Florida researcher who's studied the
protective value of mangroves in Florida, said they're an incredible tool
when used correctly. In places like Cutler Bay, huge swaths of mangroves
provide a barrier between the 10-footplus waves from hurricanes and
populated areas.
"If you have a narrow urban mangrove planter, it doesn't cut it," he said.
"Three meters of mangrove does nothing. It's a token for the look. If you
want to dissipate waves, you need at least 100 meters."
This math was evident in the federal government's decision that the best
method to protect Miami-Dade's coast from the punishing hurricanes of
the future was a 20foot wall stretching for miles along the coast, and not
the dense mangroves and short seawall combination many residents
brought up in public meetings.
Ultimately, the county and its residents rejected the wall, sending the U.S.
Army Corps of Engineers back to the drawing board for a new solution that
Miami -Dade residents will actually like, and one that is intended to protect
them for decades to come.
Page 2 of 8
An aerial view of the current conditions at Brittany Bay Park, where Miami Beach
plans to spend $1.8 million renovating the park and fleshing out a living shoreline
with mangroves. City of Miami Beach
HOW DO MANGROVES STACK UP?
It's not that seawalls are better than mangroves 100% of the time, said Rik
Gijsman, a coastal engineer and researcher at the University of'Iwente in
the Netherlands. In a 2021 paper, he and other authors analyzed a decade's
worth of research on how well mangroves work at reducing flooding
compared to a seawall.
"It's not an 'or' question. It's different systems and they can both be useful
depending on the conditions locally," he said. "I think we need both and it
depends on the local conditions, how to integrate the two."
READ MORE: Sea rise prompts Miami -Dade to consider raising heights of
roads, seawalls and canals
Rod Braun, climate strategy director for The Nature Conservancy, said
mangroves have a long list of benefits, including erosion control, providing
a habitat for the fish and other organisms that inhabit the bay, improving
water quality and storing carbon dioxide, a greenhouse gas that causes
global warming. And unlike a concrete wall, they actually form a stronger
and higher barrier over time.
Page 3 of 8
"I think it makes it just a nicer place to live," he said.
And seawalls have issues. When waves crash against the hard concrete, it
carves away at the sand below, making it a less friendly place for sea
creatures or plants.
On Jan. 26, 2022, scientists with the Department of Environmental Resources
Management (DERM) navigate by Crescent Island B, part of the county's former
living shoreline projects on Biscayne Bay. Living shoreline projects utilize a
variety of materials such as wetland plants, oyster shell, coir fiber logs, sand,
wood, and native rock. Pedro Portal
Combining the two, known as a hybrid approach, solves a lot of those
issues. It's what the city of Miami suggested for the new coastline of
Morningside Park, a 6-foot seawall in combination with mangroves and
other landscaping. Then some residents complained that mangroves would
ruin their view and they were removed from the project.
But in the case of the Army Corps plan, which was designed to protect the
county from the punishingly high waves associated with hurricanes and
not just occasional flooding, the data show that even a hybrid approach
might not be enough.
Gijsman said studies consistently show that to cut huge waves down to size
takes a lot of mangroves, an Everglades -sized amount of mangroves.
Page 4 of 8
"Mangroves will never provide full safety for real storm surges," he said.
"To really attenuate the waves you need kilometers of them."
THE SCIENCE IS STILL OUT
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Yuepeng Li, a Florida International University researcher who's published a
multiple papers attempting to quantify exactly how much protection v
mangroves offer, said there are a lot of factors when it comes to figuring o 7.
that out. It matters what species of mangrove you're talking about, and v) 0 0
even the ratio of roots to branches makes a difference.
Accounting for those variables, he said, it takes about half a mile worth of
mangroves to lop off even one foot of storm surge.
"Even one mile of mangroves, I don't think it will significantly decrease the
surge," Li said.
The city of Miami plans to redevelop Jose Marti Park in Little Havana to better
withstand sea level rise, including a living shoreline of mangroves with a floating
boardwalk around them to maintain the view. This is an outdated rendering of the
project, which no longer includes the viewing tower by the river. The city of Miami
declined to make newer renderings available to the Miami Herald. Curtis +
Rogers Design Studio
Page 5 of 8
One of the reasons builders stick with seawalls over mangroves, Gijsman
said, is that you can build a concrete structure exactly the same way every
time and all but guarantee the same performance.
"We've realized for a long time already that natural area contributes to
flood protection, but it's not that simple to work with because nature is
unpredictable, and as an engineer, you want to be on the safe side," he
said.
For instance, engineers can calculate what it would take to make a seawall
crack and fail. When it comes to mangroves, they aren't as sure. That
makes it difficult to provide the "return on investment" numbers agencies
like the Corps rely on to make decisions.
And as the world gets hotter, wetter and saltier, mangroves could perform
worse.
`Living' shorelines featuring mangroves instead of plain sea walls are popular with
climate activists, but permitting and public resistance in Miami -Dade makes them
tough to build. BY PEDRO PORTAL #
Page 6 of 8
BEST OF BOTH WORLDS
When armoring the coasts, seawalls and mangroves aren't mutually
exclusive solutions. Increasingly, planners are looking to combine both
strategies.
Landolf Rhode-Barbarigos, an assistant professor with the University of
Miami's college of engineering, said he's "all about the hybrid" of the two
— using a seawall to protect against flooding and plants like mangroves to
bring in the environmental benefits.
A rendering depicting what the Army Corps of Engineers' proposed 10-foot high
walls designed to protect downtown Miami from storm surge flooding might look
like on the Miami River alongside some nature -based solutions like a living
shoreline. Curtis + Rogers Design Studio and the Miami DDA
But calculating those eco-friendly additions is much harder than simply
seeing how much less flood damage a city faces with or without a seawall.
Not everyone agrees on the value of having a few dozen fish around or a
few pounds of carbon dioxide sucked out of the atmosphere.
Rhode-Barbarigos said if planners change the question they ask at the
beginning from 'what offers the best flood protection?' to 'what does the
most good for this space' then a hybrid solution is the clear winner.
Page 7 of 8
"What you're getting with the hybrid, T want to believe, is the best of both
worlds and not the opposite," he said.
ALEX HARRI S
IF are 6, 305-376-5005
Alex Harris covers climate change for the Miami Herald, including how South Florida communities are adapting to the
warming world. She attended the University of Florida.
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