Sea Level Rise–Can’t We Just Do What the Dutch Did?
Building dykes and seawalls to hold back rising sea level seems like an easy, if expensive, solution to Climate Change. But look closer, and you’ll see cracks in the logic that turn into disastrous floods.
“If the Dutch can do it, so can we.” You hear that statement a lot, about protecting coastlines from sea level rise – you just build levees and seawalls like the Dutch did around Holland.
But it’s not that simple. Take for example 6 feet of sea level rise in the lifetime of a child born today – a very plausible scenario for the East Coast. This might leave you to believe that if you simply build a 6 foot levee, you will be protected. But that reasoning doesn’t account for the possible storm surges that might top the levee. Hurricane Ian showed us how dangerous storm surges can be to communities on the coast.
“Superstorm Sandy” had a 9 foot storm surge when it hit New York City. Unfortunately, it hit at high tide, resulting in a storm tide (feet above average sea level) of 11 feet, causing $19 billion in damages. By one estimate, that’s a 1 in 260 year event. The Dutch, on the other hand, design their levees to withstand a 1 in 10,000 year storm. They use such a high safety factor because their levees are quite high, and therefore the damage if the levees are topped is also very high. And consider very simply that if a person lives to be 100, then there is roughly a 1% chance they will experience a storm breaching the levee – not a pleasant thought if your house is below sea level.
The higher the levee, the greater the potential damage if water tops it – it’s much easier for example to survive 3 feet of water than 15 feet. That’s why many planners are inherently a bit uncomfortable with large levees – they create the illusion of total safety, when in fact they dramatically increase the impact if the levee fails.
Earthen embankment. Man-made hills protect many Dutch cities, but they’re costly to build, and many will be overtopped by flooding from increasingly common monster storms.
But let’s get back to building our levee. How high a levee would we need to build to protect a low-lying city on the coast with 6 feet of sea level rise? Storm surges vary a lot based on the topography of the coast and other factors, but if we just look for example at what is needed for a 9 foot storm surge with 6 feet of sea level rise, we will need at least a 15 foot levee (referenced from high tide) to prevent water coming over the top. How much would that cost? The Dutch tell us that the cost of a simple earthen levee increases dramatically with height. So a 15-foot levee of this type is roughly 5 times the cost of the 6-foot levee we first imagined.
The Next Big One
"The higher the levee, the greater the potential damage if water tops it – it’s much easier for example to survive 3 feet of water than 15 feet.”
And what about that 1 in 10,000-year storm? There are virtually no estimates in the US for 1 in 10,000-year storms, but we can safely assume that the storm surge will not be small. Since we don’t even protect now for a 500-year storm, it is hard to imagine who is going to pay for all this. Of course, we can think of other more elaborate (and expensive) “Dutch” approaches like movable dams/gates to protect certain areas from storm surge, but it all gets back to not being that simple or cheap to just “do what the Dutch did.”
What if we just didn’t protect for storm surge? After all, we don’t always do that now. But the storm surge is what caused the $19B in damages to New York City with Sandy. And Swiss RE, a major re-insurance company, estimates that due to more intense storms and seal level rise, a similar storm in 2050 would cost $90B in damages. If you are going to protect “like the Dutch do,” then you need to consider the storm surges.
An Ongoing Expense
Let’s assume that you managed to raise the money to build the 15 foot levee, overcame the objections of all the influential people whose views you blocked, and finally built it. You’re finished, right? Not really, because those same estimates that say we could have 6 feet of sea level rise by 2100, indicate that sea level does not stop rising at that point – in fact it accelerates, possibly exceeding a foot or more per decade for hundreds of years. In other words, your levee is a never ending construction project.
Ever higher? With current predictions, we’ll have to regularly build taller to keep up with sea level rise.
If we keep on our current high emissions track, and the sea level rise projections we used above come true, at some point, we just have to admit that a levee does not make sense, and that the only effective solution is to pack up and move to where the water cannot get to you. That may seem like a radical idea now, but maybe not in 30 years after we have spent a lot of money on levees, while at the same time the sea level and cost estimates have just kept rising, with no end in sight.
How do we make sense of this? Sea level rise projections do vary, but one thing all the experts agree on is that the chance of 6 feet or more of sea level rise by 2100, and the very high rates after that, go way up if we don’t cut emissions quickly.
The most sensible way to reduce danger for our coastal cities is to cut emissions to net zero, and fast. One act of Congress is a good start. But it’s just that. A start.