Guest Essay by Kip Hansen
Miami Beach has a vice – a bad one – a dangerous one.
Miami’s vice is water, as in waterfront. Everybody seems to want a house on the waterfront, a house on a canal, with a boat tied to the dock.
So what’s not to like about that? After all, my wife and I live on our boat.
The New York Times (and the LA Times) has been running story after story about Miami flooding, Miami King Tides, Miami sea level rise threating billions of dollars of infrastructure.
These news pieces offer images such as:
This first image is hurricane storm surge impacting a millionaire’s beach house, built less than 10 feet above mean high tide.
High-stepping to avoid regular flooding from high tides…street built at mean high high water (MHHW). [Note: All of these named tidal datums are defined here.]
Typical canal scene in Miami (city, not beach). The mean high water line is clearly visible on the sea wall by the boat house on the right, with a safety margin of a foot or so, but no more than that. The sea wall on the left is not quite so high.
This image is actually Fort Lauderdale, but typical of Miami as well, with a flooded low lying street.
This corner, photographed hundreds of times, is Alton Road and 10th Street. Built below the level of mean higher high water (MHHW) in the canal a block and a half away, floods at every higher high tide, offering wonderful photo opportunities for every budding journalistic photographer wishing to illustrate how Miami is being overrun by rising seas.
Built below high tide? Yes, exactly. One would think that with the advent of modern surveying technology, adequate for the purpose as early as the 1950s, that roads in American coastal cities would be built at least above the predictable daily high tide marks. However, Miami is an exception [one of many, unfortunately].
Another famous Miami area intersection…let’s look a little closer:
Even though there is still about a foot clearance at the seawall, the intersection itself is below the level of the water in the canal……gotta love this kind of civil engineering.
Here is Miami Beach, showing the water levels at Mean Higher High Water:
MHHW [mean higher high water] is the level of the water at the higher of the two daily high tides. The mean of those “higher high water” levels is the MHHW – what we normally would consider the High Tide Mark. The bright green areas are “low lying areas”, known to be below this level. These SLR images are courtesy of NOAA at https://coast.noaa.gov/slr/ .
While we’re here, let’s look at the data for sea water levels in Miami. This one image contains almost all you need to know about this problem:
I would have liked to re-do all the numbers to be relative to Mean Sea Level [MSL], but have settled on adding in the numbers in red giving the levels above MSL and on the right, the levels above Mean Higher High Water (the “high tide line”).
To summarize, for those who read words better than images: The highest astronomical tide (a tide cause by the moon, sun, etc, not storm surge) was one foot above the normal MHHW. The highest observed water level was 1.77 feet above MHHW. These levels occurred in the 1980s and 90s. They are historical, as opposed to speculative or modeled future levels. Note that on the left, at about Mean Sea Level, is a little red bracket ( [ ) that represents the calculated (but not measured) sea level rise in Miami over the last 30 years, just under three (3) inches, which is about one tenth (1/10th) of the range of the tide, from low to high, which averages about 32 inches.
Now, let’s look at Miami, with our NOAA sea level viewer, for a sea level one foot above MHHW [ remember, the first sea level image above was for Mean Higher High Water (or for landlubbers, the high tide mark) ]:
Circled in light blue are the areas that we see over and over in the MSM – those areas that are guaranteed to flood during the highest of predictable astronomical tides. One of these areas includes Alton and 10th (second up from the bottom) and almost the entire Miami Golf Club (green means low lying areas not actually connected physically to the sea by a water way). Not that bad, really, except that the areas that appear as light blue pixels will be filled with sea water at every above-average high tide.
But that data table from NOAA shows that sea water levels have been observed – historically known to have taken place and recorded – as much as 1.77 feet above MHHW. NOAA does not offer the ability to see what 1.77 feet (just over 21 inches) of additional sea water looks like, but we can look at 2 feet (which is just 3 inches more):
Light blue pixels represent flooding from sea water.
This problem has nothing whatever to do with sea level rise. It is a civil engineering problem of almost unimaginable magnitude. This city has been built – for all intents and purposes – almost precisely at predictable, recurring sea levels. It is already inescapably flooding from normal predicted tides and it will continue to flood unless sea level drops a foot or two, which is not going to happen during this millennium.
But wait, it gets worse. What was the highest ever observed sea water level? The Maximum? 35 inches above
MHHW MSL. (correction h/t Brigantine and notwhatbutwho) What does that do to Miami Beach?
The sea water level was that high in 1984. City officials were all alive to witness the above flooding event. They are well aware that this level is possible without some great change to the natural system – it doesn’t take global warming sea level rise to flood Miami Beach to this extent.
How much has sea level risen (calculated as there are no existing tide gauges in Miami that have NOAA’s required thirty-year’s of data) in the last 30 years?
Just under three inches, at a calculated rate in the 2.0-2.5mm/year range (NOAA, personal communication). That’s about the thickness of two (2) US pennies. This sea level rise consists of actual rising sea levels and the geological subsidence of the land at a rate of 0.6 mm/year – about 18 mm or 0.7 inches over the same 30 years. Let me remind you that it doesn’t matter at all if the sea is rising or the land is sinking, or both – all sea level problems are entirely local consisting only of the physical relationship between sea water levels and the local land mass.
Take Home Messages:
Miami Beach is at such grave risk of sea water flooding today that it should preemptively be declared a disaster zone – not because of global-warming-driven sea level rise but due to a seeming total lack of sensible civil engineering standards and sensible building codes.
Much of the above-ground infrastructure of Miami Beach was originally built on land in areas known to be below historical highest water levels (Maximum), and some of it built below normal highest tide levels (HAT and MHHW) – to make matters much worse, much of it is intentionally connected to the sea by canals cut for this purpose.
Almost all of the underground infrastructure is below Mean Sea Level – this means utility cables, water lines, sewer lines, basements and storm drains. All subject to sea water intrusion and the resulting corrosion. Most of these features of a modern city have to be protected by pumps – which must have electrical power to continue to operate. Sewage must be pumped up into sewage treatment plants – storm drain water must be pumped up and back into the sea — it will not move when the power is out.
Hurricanes, the biggest natural disaster threat to the area, in addition to the terrific damage caused by the forces of high winds and surf, can dump inches-to-feet of rain causing fresh-water flooding, raise sea level with storm surge causing sea water flooding and knock out power transmission lines thus stopping or destroying most of the pumps that keep Miami Beach’s infrastructure going. Auxiliary generators can only keep going for so long before running out of fuel; fuel which cannot be delivered across flooded causeways and through flooded streets.
The slow inextricable rise of the sea – the majority of which is down to the geological recovery of the Earth from the last Ice Age – will continue at a rate somewhere between 2.0 to 2.5 mm/year — equivalent to 8 to 10 inches over the next century. The entirety of southern Florida will continue to subside (move towards the center of the Earth) at a rate near 0.6 mm/year equivalent to 2/10th foot or 2 1/3 inches over the next century. (The expected sea level rise includes the expected subsidence.) Nothing mankind can do will stop these processes – they must be reckoned with.
Some areas of Miami Beach (and other seaside cities built on barrier islands, sandbars and/or built on fill in tidal zones) will suffer higher rates of subsidence as soil is slowly washed out from under the buildings and roads by the coming and going of the tides in nearby waterways – a process that can be abated only at great expense.
Sea Level Rise, regardless of cause, is a peripheral, minor issue to the problems Miami Beach has with the sea – Miami Beach is already a century behind** in implementing mitigation efforts if it wishes to survive in the long run as a viable modern city.
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** Miami Beach was once a pleasant seaside resort and agricultural community on the sandy barrier island off of Florida’s southern coast. It should have been left that way. If development was imperative it should have been subjected to long-term realistic planning that would have prevented the present-day disaster-in-waiting.
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Author’s Comment Policy:
I’ll be happy to answer your questions and give more references if anyone wants them.
My biggest fear for Miami Beach and many other similar areas along America’s eastern seaboard is a repeat of the 1900 Galveston, Texas disaster.
I have never lived in Miami Beach, but have lived in Cocoa Beach, Florida, which suffers similar problems, which had a near miss with Hurricane Matthew. We have friends there (on the Banana River side) who lost their entire riverside front yard in Matthew. Their home is 2 feet above Mean High Tide.
You may contact me by email at my first name at the domain i4 decimal net if you wish.
This essay is not about climate change (under any name) – please restrict your comments to the issues discussed. If your comment is specifically addressed to me, please indicate so by using Kip as the first word — like “Kip, please explain why you say…”
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