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Sutro, Fog Catcher

January 6, 2014
tags: , ,

The drought, it is coming. Rainfall totals for various Northern California cities in 2013 via the Mercury News.


And drought GIFs, naturally:


The dog days of reservoirs.


This is especially bad since we in California get the most of our water from the Sierra snowpack. Uh oh.

2014 Jan snowpack

Hetch Hetchy is a geo-engineering marvel, but you have to start wondering what happens when the Sierras start looking like Baja California.

hetch hetchy system

@mizmay reminds us that we actually have decent groundwater in SF.

These would be Islais, Precita and Dolores Creeks:

“the fresh spring waters indefatigably flowing on the eastern slopes of Twin Peaks are a wondrous geologic feature, of unknown origin and potentially great benefit to the city. This water comes in quantities and seasons unlikely to be associated with local rains. Further study is needed to determine its ultimate source.”

precita, islais, dolores creeks zoom

Of course, it’s always nice to have backups. This is why I demand that Ed Lee immediate tap the aquatic reservoir that is… @KARLTHEFOG.

There is a precedent to this in South America. Residents of Lima are building “Atrapa nieblas“, or fog traps. On a good foggy day they can capture 150 gallons of water.


We of San Francisco, being awesome, can do better than that. First some math. Fog contains anywhere between 0.05 and 0.5 grams of water per cubic meter. Karl, being Karl, is obviously 0.5 grams. Assuming half the city is covered in fog at a depth of 1000 feet (i.e. the top of Twin Peaks):

49 square miles / 2

= 63,454,700 square meters * 300 meters

= 19,036,410,000 m* 0.5 grams

= 9,518,205,000 grams = 9,518,205 kilograms = 9,518,205 liters = 2,514,440 gallons.

That’s a sphere of water 43 feet wide, or a cube 70 feet on a side.

Problem solved! OK, not really, as I do not have a realistic method to collect fog over half of San Francisco. However, a short term solution would be to retrofit Sutro into an atrapa nieblas:

sutro atrapanieblas

Simulation of it in action:

sutro fog catcher

(original photo via DailyKos)

A quick calculation shows that with a surface area of 300 by 300 meters, and a 22 mph wind (10 m/s), our modified Sutro could catch 100 gallons per sec.

Not too shabby, Sutro, not too shabby. If @karthefog is around for 12 hours, that’s over 4 million gallons!

UPDATE: Sarah Zhang wrote a great followup article over on Gizmodo about other fog catcheries:

7 Comments leave one →
  1. TrixieSF permalink
    January 7, 2014 7:59 am

    My building is on the stream that runs through Sanchez and “Temple” on your map. Normally by this time of year there’s a big permanent wet patch on the sidewalk from it but this year, nothing.

    Related question: do these streams empty into the storm sewer system now? The storm drains on that corner back up during heavy rains but I’m not sure if it’s that or just cause it’s a low spot.

  2. January 8, 2014 4:02 pm

    Just like the 80s! Except now I want to ski even more. Gosh darn it!

    Time to fill kegs at El Polin spring for the end times until you get Sutro up and running… Can we create reservoirs we can swim in on Twin Peaks? Windmills at the top of the tower to heat them?

  3. January 9, 2014 6:42 pm

    Or we just all wear stillsuits.

  4. July 7, 2014 12:03 pm

    Hi Burrito Justice,
    I loved your post! I am currently working on a project with McCall Design Group in SF re-imagining the potential of the urban backyard if all fences and dividers were removed. Do you think that fog catchers would accumulate enough water in the Inner Richmond district to support public gardens? I’d appreciate your feedback and comments.
    You can follow my project here:


  1. Could Fog Catchers Help Solve America's Drought Problem? | Gizmodo Australia
  2. California Goes Dry, But The East Bay Has Plenty Of Water | Greg Fielding
  3. Could Fog Catchers Help Solve America's Drought Problem? | Hihid News

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