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News and Features

November 2022

Architecture, Engineering
and Construction (AEC)

Florida Hurricane

Figure 1:  Convection image of hurricane (tropical cyclone) nicknamed “Ian”, 28 Sept 2022, making landfall in SW Florida. Yellow, orange and red indicate updrafts in order of intensity (yellow strongest). Notice yellow area in Atlantic Ocean which (due to storm rotation) caused heavy rain in NE Florida. [NOAA]

On 28 September 2022, a Category 4 tropical cyclone, officially nicknamed “Hurricane Ian”, made landfall around Fort Myers on the SW Florida coast. More than a month later, flooding from the storm’s heavy rains is still receding in Northern Florida, due to river constricting infrastructure downstream.

Most of the terrestrial storm damage was preventable, had there been adequate design and construction of buildings and roads.

The storm had less wind velocity and lower storm surge than the 1935 Florida Keys Hurricane, but was wider, which is typical of storms that are not maximum strength. These types of tropical cyclones, that do not reach full intensity, can be wider and dump more rain.


Home Construction

The biggest mistake associated with this hurricane was the existence of single story buildings without a full story of storm surge passage underneath each building. Those buildings were washed away, while houses on stilts survived as expected.

Figure 2:  Aerial view of a Fort Myers Beach neighborhood, the day after the hurricane. Houses on stilts designed for storm surge survived, while other buildings were washed off their properties. [AMO]

Figure 3:  Lower mid portion of the preceding photograph. The following two figures are portions of this figure.

Figure 4:  Houses A and B (upper right) are resting where the storm surge pushed them. House A is from Property A, and House B is from Property B. House A was single story (should have been on stilts). House B was two story, but the lower floor was sealed with brick facade (did not allow storm surge through). Notice the undamaged dark blue building with white roof (upper left): the downstairs is parking spaces for automobiles, with slats to allow storm surge to flow through.

Figure 5:  The single-story building that is under the crane boom (left) was pushed there by the storm surge from the concrete pad in lower right. Notice automobile floating sideways (right). While buildings with sturdy construction on stilts can survive a storm surge, automobiles cannot survive a storm surge and need to be evacuated. Electric vehicles are not recommended because they will cause the electric grid to fail if everyone tries to charge the vehicles at once when evacuating, and because salt water flooding causes permanent damage to the electric vehicle batteries.

Even though the Gulf of Mexico is not shallow compared to rivers, the Gulf of Mexico on Florida’s west coast is much shallower than the Atlantic Ocean on Florida’s east coast. That makes Florida’s Gulf coast more prone to hurricane storm surges, due to the frying pan effect: strong winds cause water to bunch up.

For example, if you pour a couple of centimeters of water in a frying pan, and position a fan to blow hard on the water, that will cause water to bunch up on the downwind side of the frying pan.

If you were to position the fan over a deep kettle of water, the water would bunch up less, because water below the surface would be able to flow back, to fill in where wind is blowing water away.


Transportation

Another mistake is the use of dike roads. This problem has already been known dating back to the 1935 hurricane.

“Some local inhabitants suspected that the bridge piers and embankments reduced the tidal flow, leading to catastrophic consequences when the 1935 Hurricane hit.”
— 
Nicholas K. Coch, “Anthropogenic Amplification of Storm Surge Damage in the 1935 ‘Labor Day’ Hurricane”

Dike roads in the Fort Myers area were washed out by the hurricane. The dikes were built of sand from the bay bottom next to the dike, leaving underwater trenches where the sand was removed from. Those dikes need to be replaced with bridges; the sand should be pushed back into the trenches it came from.

Figure 6:  Washed out dike road (center) that had connected two bridges (left and right) which were not damaged by the storm. No bridges were damaged by the hurricane. Only the dike roads failed. All the dikes should be replaced with bridges. The state government calls this dike a “sand bar”, even though it is artificial (real sand bars are parallel to water flow; this is perpendicular to water flow). This dike should be replaced with a new bridge that connects these two bridges. [AMO]

Replacing dike roads with bridges in an estuary improves water flow even when there is no storm. And bridges require much less storm repairs than dike roads, freeing up resources to work on other needs.


Flood Drainage

As of early November, flood waters from this hurricane are still receding in Northeast Florida, due to capillary restriction of the St. Johns River, which is Florida’s longest river.

The river flows south to north, and has less hydraulic head (vertical drop) than other rivers in the United States, making it a capillary flow river. Infrastucture development of the past century has restricted the capillary flow near the mouth of the river, increasing flooding upstream.

Capillary flow rivers flow better if the water surface is wider downstream. Historically, the St. Johns River had gradually sloping banks that would allow flood waters to submerge the banks to widen the river surface.

That would also cause some erosion, allowing the river to get even wider next storm. After a series of storms (over centuries), this erosion would allow upstream flooding to drain faster, reaching an equilibrium of reduced flooding that causes less erosion.

The problem with the St. Johns River is that it has been restricted with dikes from Jacksonville to the ocean, reverting the upstream flooding to pre-erosion levels, but without allowing the pre-erosion flooding to cause erosion to reach equilibrium that reduces future upstream flooding, essentially locking in more flooding upstream.

In other words, “reclaiming” land that is supposed to flood. Or to put it another way: eliminating a river delta that would have allowed upstream flooding to drain faster.

To understand how this works, two concepts are needed:

In order to push water through pipes, there needs to be either a vertical dropoff (called “head”), or there needs to be compressed air pushing the water from behind. Water itself does not compress. It takes air to use compression to get water to move.

For example, to distribute water via pipes, a water tower can be used. Water is pumped up to a tank on a tower. From that tank, water is gravity fed into the pipe when a faucet is turned on.

The water tank could be positioned on a hill instead of on a tower, also using gravity feed.

A more common way to deliver water in pipes is to have an enclosed water tank that has an air pocket within the top of the tank. When water is pumped into the tank occasionally, the air pocket compresses, creating pressure that pushes water out of the tank when someone turns on a faucet.

Figure 7:  Underground cistern water supply: Pump (1), in well (2), pumps water into tank (3). The tank has air within the top of the tank. As water is pumped into the tank, the water level goes up, compressing the trapped air. The compressed air provides “water pressure” to push water, from lower in the tank, up through pipes when a faucet is turned on. The pump only needs to turn on once in a while, just enough to keep the tank water level high enough to keep the air compressed. It is the air that is being compressed, not the water. The compressed air pushes the incompressible water out of the tank when a faucet is turned on. [SamuelBailey]

The air pocket is necessary, because water does not compress.

Water also has surface tension, caused by each water molecule sticking together (having stickiness) with its neighboring water molecules.

This tendency of the same type of molecules to try to stick together is called cohesion. It causes water to form drops, and causes a glass of water to not overflow even if you pour it a little too high.

The surface tension of the water (that is poured a little too high) causes it to be able to have a surface height slightly above the height of the side of the glass:

Figure 8:  The top edge of a glass of water, showing water level slightly higher than the top of the glass. [StevenLek]

Molecules also try to have stickiness with other types of molecules, not just the same type of molecules.

While cohesion is the term used to describe stickiness of the same type of molecules to each other, adhesion refers to molecules having stickiness with other types of molecules, for example stickiness due to friction of dissimilar materials.

In this example, the water molecules are having more adhesion to the glass molecules than to the air molecules.

The more surface area contact that molecules have with an adhesive material, the more adhesiveness occurs. Or, to put it another way, the less contact with an adhesive material, the less adhesiveness occurs. This is called capillary action.

Figure 9:  Capillary action of colored water defying gravity in glass tubes. The water molecules have more tendency to adhere to glass than air, causing higher water level in smaller diameter tubes because there is more glass contact of water molecules in the smaller diameter tubes. [USGS]

The United States Geological Survey has a good video about the capillary action of water:

USGS Capillary Action video

For a body of water (lake or river) that has slow flow, the flow will be faster if it is wide and shallow, than if it is deep and narrow, because the wide flow will have more air contact that provides less friction.

Figure 10:  Water molecules on the surface have less contact with other water molecules than water molecules that are not on the surface.

With the wider flow, there is less resistance to flow because more water molecules are in contact with air, instead of in contact with other water molecules.

The resistance of water to shear is called viscosity. Slow moving water could experience considerable resistance from viscosity if it is deep (limiting water flow to only some of the depths).

Historically, the banks of the St. Johns River had gradually sloping banks, that allowed rising water to naturally widen the river, speeding up drainage of upstream flooding. Infrastructure from the past century, however, is blocking that, causing bottlenecks with deep narrow water, not suitable for capillary river flow.

Figure 11:  St. Johns River shoreline, Jacksonville, 1918.

Figure 12:  St. Johns River shoreline, Jacksonville, November 2008. [JasonDuhon]

Figure 13:  Nautical chart of the wide mouth of the St. Johns River in 1853. [NOAA]

Figure 14:  The artificially narrowed mouth of the St. Johns River, with jetties (dikes) extending into the Atlantic Ocean.

The sides of the river are completely diked-in all the way from the ocean to Jacksonville, with only intermittent openings that allow too little water to flow into the former river delta.

In geologic time, the St. Johns River may have been flowing southward (opposite direction of current flow), and emptied into the Atlantic Ocean 200 km south of its current mouth, according to geomorphological research of the area. The low hydraulic head of the river would have made it susceptible to reversal of flow direction, by possible regional geologic uplifting (would not have taken much uplifting).

The recent artificial narrowing of the current mouth of the St. Johns in just the past century has prevented the river from using erosion to finish building its current delta, and even reverts the river to an earlier stage of delta development that increases upstream flooding.

Major urban and industrial infrastructure that needs to be built near a coast should be built away from river deltas, especially the river deltas of capillary rivers. Allowing slow moving river deltas to widen provides more water flow through the delta, which through cohesion pulls more water from a capillary river.