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Comment by Gimpei | Hacker News Reader

How is this issue affected by rising sea levels? I'd think that those beaches are doomed anyway and not even sea walls are going to save those houses.

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The beach erosion is accelerated by the presence of walls [1].

In general the regulation of seaside buildings is extremely lax in the US, and this takes a toll on the beaches. As a counter-example, in Greece seaside houses must be built at least 30m inlands from the end of the beach. It is also illegal to cut-off public access to the beach.

[1] http://www.beachapedia.org/Seawalls

The only cause-effect given in your linked article I saw was:

“Active Erosion - Refers to the interrelationship between wall and beach whereby due to wave reflection, wave scouring, ‘end effects’ and other coastal processes the wall may actually increase the rate of loss of beach. This is site-specific and dependent on sand input, wave climate and other local factors.”

I didn’t see any explanation in the article (however I couldn’t scroll past the map part way through the article because I was using a touch device - grrrrrr).

You've also missed passive erosion. Obviously, specific numbers can't be given because the effect varies with the specifics of each beach. But it's not really rocket science, at least if you have ever lived close to a beach.

To preserve a beach, you need the waves to leave behind as much solid material as possible. In an open beach, you can observe much of the wave being "absorbed" by the beach rather than "pulling back" in the sea. When the wave is "absorbed", any solids carried by the wave settle on the beach.

If you place a wall on the beach: (a) you prevent the waves from reaching further inlands where they have been attenuated so they can be "absorbed" and leave the solids they carry behind, (b) you force them to "pull back" while they still carry a lot of energy, which will also carry away some of the existing solid material on the beach.

Or, if you prefer a mathematical explanation, the waves shape the beach so that its vertical gradient is a continuous function. If you force a discontinuity (wall) in the gradient, the waves will shape the beach so that there is no discontinuity. I.e. either the wall will be destroyed, or the beach will erode and the waters will become deeper.

The houses are doomed. Anything built right next to the ocean is temporary, and if you were dumb enough to put millions into a fancy house there, that should be taken as an expensive lesson.

In the absence of seawalls, the beach will advance as the ocean rises, but the loss they're describing is far in excess of anything caused by sea level rise.

>The houses are doomed. Anything built right next to the ocean is temporary, and if you were dumb enough to put millions into a fancy house there, that should be taken as an expensive lesson

Everything is doomed in the long run. Most of those houses look like they could withstand the <=1 meter sea level rise expected by 2100. That is generations of owners enjoying them and making profits. I imagine at some point the home value will start to decrease, but that could be gradual and a long way off.

The "expensive lesson" for the next several "dumb" owners could be that they owned a beautiful house and sold it for millions more than they bought it.

I think the problem is that even if the houses are far back enough that they are 1m about sea level, they are now at extreme risk of destruction if there is a major weather event where they might have previously avoided it.

I don't think it is fair to say that they are now at an extreme risk of destruction.

Risks always exist. The risk of flooding is probably some small percent higher than it was 10 years ago, and 10 years before that. The risk will increase over the next 100+ years until the homes are destroyed.

It seems like a problem that will work itself out. Either insurance will go up, the house value will go down, or both.

In the mainland US, houses right on the shore that are likely subject to storm surge are covered by some kind of government program since private insurance won't touch them. I have forgotten the details, unfortunately.

> that should be taken as an expensive lesson.

haha, laughs in global financial crisis

Haven't been paying attention? Rich people never have to learn lessons. Never.

In the long term, you are probably quite correct. In the short term though, the sea-walls give an impression of safety and protection, allowing the owners to sell their properties at great profit before the values collapse.

Here in New Zealand, waterfront property owners have been making legal attempts to block authorities from placing warning notices in the Land Information Memorandum (LIM) documents. These LIM documents are examined by lawyers when a property is being purchased, so to have a warning about your property in the LIM can seriously affect the value of your property.

Lawsuits to prevent people from hearing about reality.

Here in Washington we have a lot of houses built far too close to bluffs, and the trees on those bluffs cut down because they block the amazing view. The views are amazing for a couple of decades. Then the bluff erodes far enough that the house is condemned.

Seattle has a special example called Perkins Lane. It is a beautiful, almost idyllic little street looking out over the water. It is also used in civil engineering classes as an example because it has every possible kind of landslide, and half the lots on it have ceased to exist over the past century. They're just water. You still see new houses being built there.

> not even sea walls are going to save those houses

I would like to believe that's true, but here in California new seawalls are a foot-thick web of epoxy-coated reinforcing bar, encased in two feet of concrete, on a foundation sunk some ten or so feet down into the sand. I have yet to hear of one of these falling down.

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