10/10/2024
WT Staff
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October 10, 2024 243 pm EDT updated October 11, 2024 1007 am
How fast can you set up an effective emergency flood wall?
Part One: INERO hard-shell barrier: built to handle moving water with debris
Interview with Peter Nero, Key Accounts Manager, INERO
recorded Tuesday, October 8, 2024
Editor's note: News from Tampa General Hospital, the storm surge was not as high as forecast and the emergency flood barrier did its job. The Trauma Center remained operational through the worst of the storm, the full services of the hospital reopen today.
WaterToday: Good evening Peter, thanks for being here. We are looking at a video here of preparations being made to secure the Tampa General Hospital, located on a peninsula in Tampa Bay, Florida where Category 5 Hurricane Milton is forecast to make landfall with storm surge up to 15 ft tomorrow night. The barrier used here is 9 ft high, how is this going to work against a 15 ft surge?
Peter Nero: Yes, thank you. That won't work. The problem is, when the water overtops the barrier, you are containing the surge inside the barrier. This could actually be worse than having no barrier at all. An inadequate sized barrier won't protect anything, the flood will just ignore the barrier, basically. Any debris comes on top of the floodwater, including boats. You can see in various flood images, there is a risk of floating debris going over the barriers with the storm surge, if the barrier is not high enough for the job.
WT: I understand some of these flood barrier products have been designed and certified for still water, not dynamic water with debris. Can you help us understand the difference?
Nero: The tensile strength, the strength between the different components, such as the face plates, the support legs or cables, might not be strong enough since the power of floating debris and flowing water is so much greater than still water.
WT: Speaking of debris, there has been a tendency in Canada to use inflatable dams as flood barriers. I have spoken to the manufacturer of one such product, the inflatable dam designed for construction dewatering with clear instructions floating debris must be removed from the water. By definition then, the inflatable dam is not suitable for river flood or even urban flash flood. Looking at the devastation from Hurricane Helene and the debris field left behind, can you explain how INERO is designed for fast-moving flood water with heavy debris?
Nero: We have done a lot of tests. All the parts of INERO barrier are designed and built much stronger than they need to be for the water alone, by a margin, a multiplier of 2.4. The solid metal pieces, 4mm aluminum face plate, the foot and support leg link securely together where the weight and pressure of the flood water is greatest. The weight of the water holds the parts together actually. In most structures, the connections between parts are going to be the weakest points. With INERO, the linkage between the face plates, what we call the lock mechanism, is designed to give more strength to the barrier. Each leg can hold up 1.5 tonnes on its own.
See the INERO Barrier, here.
WT: Can you explain the different profiles we see in the various barrier products? INERO is angled back and away from the floodwater with the smooth part facing the flood impact. I see other barriers set up perpendicular to the ground with the supports being on the wet side. Can you explain the practical or functional difference of these two options?
Nero: Yes, the weight of the water is part of what holds the INERO barrier together and holds it down in place. With the 90 degree barrier, the weight of the floodwater is acting against the supports, to force the barrier out and away from its support cable. When there are heavy winds, as there usually is with floods, the forces are working to break the barrier apart. With the angled face plate toward the flood and debris field, you won't get a direct hit to the barrier structure, the angle slows the impact of the water and floating debris, and of course the INERO barrier cannot be punctured.
You need to be ready for the weight of whatever comes, logs, cars, boats, everything. This could be a problem for the upright profile barrier, I have not seen it in action but it does not look good. You have to be sure the barrier is sized for the situation, if the water depth gets too close to the maximum height, the wind could overwhelm the barrier and cause it to fail.
WT: WaterToday reports flood flow volume and depth from the network of streamflow monitors of the United States Geological Survey (USGS). By those sensors, you can see how deep these rivers can get during flood events, and how fast they get there. Emergency responders can use this information to plan for assembly of barriers, as you can see how long it takes from one location flooding to the next downstream location. If the municipality plans to contain these rivers inside the natural channel, how does INERO work in this case?
Nero: In setting up to follow the river channel, the teeth of the foot piece grip into the ground. The flexible lock mechanism between the face plates allows the barrier to bend and follow the curvature of the riverbank. When you deploy in emergency situations, you can start setting up from many places at once and secure the joins by overlapping the plates. The time to set up also depends on the transportation of the barriers to the location, the logistics, that's another layer that must be considered. It is best to store the barrier as close as possible to where it will be used. The steel crates are designed to stack three to four high, so they can be stored efficiently in a warehouse. It could be stored outside, it does not rust, it just gets a bit ugly.
WT: The crates weigh how much?
Nero: 1.3 tonnes for the 1m high barrier.
WT: I understand the only time you need heavy equipment is when dropping off the crate, is that right? Each of the barrier pieces can be managed by one person?
Nero: Yes, exactly. The crates are packed up with 100m or 50m barrier in each (80 cm or 1m height profile), two crews can work from one crate and set up in two directions at once. Even if it starts to flood, the crews can continue setting up without additional tooling, we say as deep as 60 cm of flood water is possible, as you don't need to reach beneath the water surface to set this up.
If there is not too much elevation change in the riverbank you can put it up as it is, or, the lock mechanism, you can link it higher or lower to follow the contour of the ground. You can drop in a higher section in a spot with a dip in elevation. If you have done your calculations correctly ahead of time, this can go very smoothly.
WT: I did not ask you about storm surge as a use-case for INERO barrier. Maybe its not even possible, what do you say about the use of INERO barrier for storm surge, and what is the maximum height of your barrier?
Nero: INERO maximum height is 150 cm (4.9 ft) with a 20 cm extension piece (total 5.5 ft) that can be added for extra margin. With storm surge, you need more margin (freeboard) to allow for wind and waves, to not over-top the barrier. If the barrier height is not sufficient for the surge expected, you should not be using it at all.
WT: Can you explain hydrostatic pressure, there is an exponential increase in the force, the weight on the barrier as the water gets higher? Have I got that right?
Nero: Yes, that's right. This is why we have stopped at 150 cm to ensure we have our margin of safety, to ensure the barrier will hold. When I see other barrier much higher, thinking of the enormous weight and pressure of so much water, I would not want to stand behind that.
WT: Now to discuss another important use-case, urban flooding. How is INERO best used in situations of overland flooding on paved surfaces that comes from excessive rainfall? In urban flooding, when the storm sewers get plugged or simply overflow, the water comes from all directions. How would INERO best be used in the city?
Nero: For the protection of buildings or property, you would set up with the face plate toward the flood, support legs and connectors to the dry side. For wastewater plants or other sites containing hazardous materials, you want to keep the floodwater from mixing with the contaminant and washing it everywhere. In this case, you would set up the barrier with the face plate toward the hazardous material to be contained, and set another perimeter of barrier angled toward the flood water. INERO can contain water or oil, or other contaminant, to keep it inside the barrier, this is a common use-case for urban flooding.
There will always be some leakage of water getting through the ground beneath any barrier. You need pumps on the dry side to pump any leakage back. Depending on the site, you can dig a hole for the pump. There are many different scenarios.
WT: Speaking of hurricanes, the wind is a huge factor. It is important the barrier sets up fast with a small crew. You don't want to be out there still setting up when that wind hits as any pieces not secured will become projectiles. Can you explain how fast this barrier sets up?
Nero: A trained crew of four can set up 100 m per hour. With a hurricane and high winds, we recommend concrete bolts or earth bolts to anchor the barrier. You can add whatever heavy material you want on the feet at the back to help hold it down, sandbags, gravel. If it is really bad winds, you may want to omit the membrane. You will get more leakage, but it might be better than dealing with the plastic membrane flying away in the wind.
WT: Last question, we are both in cold countries and our flooding often starts in the spring thaw. If we were setting up to control flooding in the spring break-up, would the teeth on these feet bite into frozen ground or ice?
Nero: Each situation is different of course. The barrier foot section has special teeth, the foot itself angles outward and is curved as well so when you get the pressure on it, it won't be in a straight line downward, it spreads out, securely adapts to the ground. Depending on how cold it is, it will bite into the ice or frozen ground. If you have water around to flood, it is likely not too cold.
WT: Anything else you want to add?
Nero: Emergency planners need to carefully consider where these barriers can help and where they cannot. If the water level is too high and there is debris floating over the barrier, it will not help. Debris flying in the wind, it will not help. You need to shift how you think about emergency protection overall, to use the flood maps, to pre-plan and practise the set up ahead of time. If part of the strategy involves construction of permanent barriers, you can use the temporary barriers to fill in between. This requires a shift the mindset, to consider all of the different protection methods you have available, being realistic about the materials strength, using the right tool in the right place. I should also add, the INERO barrier is one hundred percent recyclable. After thirty years of use it will still have its full value in the raw material.
WT: One last comment, it is so hard to watch. While these dreadful flood events are happening in the USA, you have 10km of INERO barrier sitting in a warehouse in eastern Canada. Can you speak to this, why do you think the barrier is still in storage when it could be in use?
Nero: It is crazy not to use it. I don't understand.
More to follow next week with How fast can you set up an effective emergency flood wall? Part 2: A flood barrier tool for every job, self-raising barrier for protection of subway entrances, parking garages
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