ALL THE DAMS AND MAGIC WETLANDS CAN DO 
Big, fat, cleared floodplains are the best way to handle a very large storm, explains wetlands scientist John Jacob — because nothing else is going to: “An average rainfall of 35 inches over all of Harris County (Harvey) is just over 1 trillion gallons. At most, there are about 50 billion gallons of stormwater detention capacity in Harris County wetlands (no one has measured this — I had to make some very broad assumptions). So that means that the wetlands at best could handle about 5% of the total volume of Harvey rainfall. In the large scheme of things, it’s not much. And the scheme of things in Harvey is indeed very large.
So much for the magic wetlands. But what about our engineered drainage system? I calculate a somewhat larger detention capacity — between our large US Army Corps of Engineers Katy Prairie reservoirs (~400,000 acre-ft) and Harris County Flood Control District detention (about 34,000 acre-feet), we have about 130 billion gallons of detention volume. More than what we have for wetlands, but still only about 14% of Harvey. As we painfully saw, also overwhelmed.
And what of green stormwater infrastructure — rain gardens, bioswales, green roofs, etc.? We don’t have any good numbers here, but you can be sure that even if these practices were widespread, the volume would be very small relative to wetlands and detention basins. These practices are designed to capture at best a 2 inch storm.” [Watershed Texas] Photo of Willow Waterhole Greenspace: Luz (license)
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The buffalo bayou disposes of large volumes of water into the gulf of Mexico. What is the equivalent detention volume of this system?
Please read the entire article. This snippet is a bit misleading. The conclusion of the article is that the only way to deal with rain events like Harvey, Tax Day and Memorial Day floods is to reclaim the flood plains through buyouts. The snippet lends some credence to the “f— it. We will flood no matter what” crowd. The rest of the article emphasizes the importance of the prairies and green infrastructure (bioswales, green roofs, etc.) to water quality and Galveston Bay. So, the conclusion is really that massive buyouts in flood plains are really the only answer to flood control but prairies and green infrastructure are important for water quality.
Sorry, I was unable to locate the longer article – how does one do that? I was only saying that if you want to calculate required detention capacity given rainfall figure, you need to take into account the portion of the rinfall that is transported to the sea by the bayous.
Oldschool
you have it exactly right. We need all of this green infrastructure, and lots of it. But the only green infrastructure capable of handling a Harvey are the floodplains.
Thanks!