Wednesday, April 23, 2014

Coastal inundation: it's the surge, not just the tide.

What’s clear to emergency managers and may not be clear to the public is this: when worrying about sea level change, it’s not the highest tide but the storm tides that should concern you.

In low-lying parts of Honolulu, as at Mapunapuna, high tides already flood streets. Annoying but not catastrophic.

Put a storm surge on top of that, and you start having real problems. Put a storm surge on top of the anticipated sea level rise in the next few decades, and low-lying areas can become uninhabitable. And finally, put a storm surge on top of sea level rise, PLUS regional sea level oscillations, and you have something even worse.

A recent study of New York’s experience shows that flooding threat has increased significantly. 

The American Geophysical Union reports that “Maximum water levels in New York harbor during major storms have risen by nearly two and a half feet since the mid-1800s, making the chances of water overtopping the Manhattan seawall now at least 20 times greater than they were 170 years ago.”

The study on which that statement is based is here

The abstract says: “Three of the nine highest recorded water levels in the New York Harbor (NYH) region have occurred since 2010 (Mar. 2010, Aug. 2011, and Oct. 2012), and eight of the largest twenty have occurred since 1990.”

There, they’re talking about a combination of a regional sea level oscillation, plus climate change-related sea level rise, plus storm surge—the terrible trio for coastal zones.

The result is that in any given year, the chance of water overtopping Manhattan’s seawall is up from 1 percent to between 20 and 25 percent.

Those kinds of conditions can occur in the Hawaiian Islands as well, threatening coastal roads, coastal homes, coastal businesses, coastal utilities and potentially turning coastal lowlands into saltwater swamps.

© Jan TenBruggencate 2014

Tuesday, April 15, 2014

Old is new again: wood as an industrial material.

Old is new again.

It seems positively archaic to use wood in mechanical applications, but it’s the newest thing.

And in many applications, wood turns out to be not only good, but in certain applications the right wood can be significantly better than the metal or plastic alternatives.

A preferred industrial timber is lignum vitae, the exceedingly hard wood that started being used as propeller shaft bearings in steamships in the middle 1800s.

(Image: The blue flowers of lignum vitae at Ala Moana Beach Park. Image courtesy of Forest and Kim Starr.)

More than 150 years later, machinists are turning back to it, for good reasons. One of them: besides being harder than some metals, it is resistant to rot, and it thrives in underwater applications.

That last feature means it can be used, for example, in ship steam engines and in underwater hydroelectric facilities, where lignum vitae bearings can be water-lubricated—reducing the risk that petroleum lubricants will damage the aquatic environment.

The online magazine describes a 100-year-old hydroelectric plant that went from lignum vitae to composite bearings, and then opted to go back to the wooden bearings for their long life.

Lignum vitae is an American tree that seldom grows to more than a foot thick, although there are records of larger ones. Trees are harvested when they are a few hundred years old. It is used for the heads of carving mallets and butcherblocks, since it’s so heavy and less likely to mar or dent metal. British cops carried lignum vitae truncheons, and heavy croquet balls have been turned from the wood.

Its fibers are dense and interlocked, making it far less likely to split than other woods.

Several similar woods are sometimes sold as lignum vitae, the real thing being Guiacum officinale or Guaiacum sanctum. There are other lignum vitae—it means wood of life—sold in landscaping, which are close relatives but not the same species.

In Honolulu, Foster Botanic Garden has an example of Guaiacum sanctum. Ala Moana Beach Park has Guaiacum offinale. And they are grown in landscaping for their pale leaves, pretty blue flowers and slow-growth habit.

A couple of species of South American trees in the Bulnesia genus, called Verawood or Argentine lignum vitae, sometimes replace the real thing in commerce. Species of eucalyptus and acacia sometimes get the title as well.

Persimmon, a member of the ebony family, is also a very hard wood that performs well in underwater applications.

Few metal bearing materials can match the history of lignum vitae. There are hydroelectric plants across the world that have been turning on lignum vitae bearings for a century and longer. They operate in fresh as well as salt water.

A company called Lignum Vitae Bearings sings the praises of the wooden material as “the only environmentally responsible renewable industrial bearing known to man.” 

© Jan TenBruggencate 2014