A reply to Felix Salmon's post, "How to protect New York from disaster"

A response to Felix Salmon's post, "How to protect New York from disaster".

Dear Felix,

Reuters' website has been very buggy lately, so I thought I'd write this down on my blog.

With a rising ocean level, it won't matter if you added a trillion square feet of green roofs and bioswales (by the way, for an example of sidewalk bioswales, see: http://goo.gl/ks7cL).

Green roofs and bioswales mitigate the need to expand sewer capacity and storm overflow, first and foremost.  Because they divert storm water into natural filtration and slow the process of rain water flow, they buffer a lot of storm-induced river flooding.

But in a hurricane or as a result of global warming, a rising ocean with salt water would end up killing most of the plants in these bioswales.  And the sheer amount of water would simply overwhelm the bioswales.  You saw what happened when the tsunami hit Japan; it's almost the same thing -- a higher, localized ocean level (whether from a storm surge or a tsunami) cannot be mitigated, even if you had a million acres of farmland.  The tsunami sea wall was their best hope, but it was too short.

If NYC is like most other cities in the US, then combined sewer overflow goes directly into a major body of water.  Bioswales and green roofs help stop storm water from entering and overloading the sewer system which in turn prevents untreated sewage from being dumped.  But what happens when the water table is so high (from either a storm surge or global warming), as to push that sewer water backwards?  You've seen it occasionally but you might expect to see it with greater frequency in the future: crap flows backwards and up into homes.

A sea wall is only just the beginning.

Sincerely,

GRRR