How do you construct a 3D model of something that lives underground and only exists in a handful of pictures taken from the interior? This was my task for the Cisterns of San Francisco last week.
The backstory: have you ever seen those brick circles in intersections and wondered what the heck they mean? I sure have.
It turns out that underneath each circle is an underground cistern. There are 170 or so* of them spread throughout the city. They’re part of the AWSS (Auxiliary Water Supply System) of San Francisco, a water system that exists entirely for emergency use.
The cisterns are just one aspect of my research for Water Works, which will map out the San Francisco water infrastructure and data-visualize the physical pipes and structures that keep the H2O moving in our city.
The original cisterns, about 35 or so, were built in the 1850s, after a series of great fires ravaged the city, located in the Telegraph Hill to Rincon Hill area. In the next several decades they were largely unused, but the fire department filled them up with water for a “just in case” scenario.
Meanwhile, in the late 19th century as San Francisco rapidly developed into a large city, it began building a pressurized hydrant-based fire system, which was seen as many as a more effective way to deliver water in case of a fire. Many thought of the cisterns as antiquated and unnecessary.
However, when the 1906 earthquake hit, the SFFD was soon overwhelmed by a fire that tore through the city. The water mains collapsed. The old cisterns were one of the few sources of reliable water.
After the earthquake, the city passed bonds to begin construction of the AWSS — the separate water system just for fire emergencies. In addition to special pipes and hydrants fed from reservoirs for hydrants, the city constructed about 140 more underground cisterns.
Cisterns are disconnected nodes from the network, with no pipes and are maintained by the fire department, which presumably fill them every year. I’ve heard that some are incredibly leaky and others are watertight.
What do they look like inside? This is the *only* picture I can find anywhere and is of a cistern in the midst of seismic upgrade work. This one was built in 1910 and holds 75,000 gallons of water, the standard size for the cisterns. They are HUGE. As you can surmise from this picture, the water is not for drinking.(Photographer: Robin Scheswohl; Title: Auxiliary Water supply system upgrade, San Francisco, USA)
Since we can’t see the outside of an underground cistern, I can only imagine what it might look like. My first sketch looked something like this.
I approached Taylor Stein, Fusion 360 product evangelist at Autodesk, who helped me make my crude drawing come to life. I printed it out on one of the Autodesk 3D printers and lo and behold it looks like this: a double hamburger with a nipple on top. Arggh! Back to the virtual drawing board.I scoured the interwebs and found this reference photograph of an underground German cistern. It’s clearly smaller than the ones in San Francisco, but it looks like it would hold water. The form is unique and didn’t seem to connote something other than a vessel-that-holds-water.Once again, Taylor helped me bang this one out — within 45 minutes, we had a workable model in Fusion 360. We made ours with slightly wider dimensions on the top cone. The lid looks like a manhole.
Within a couple hours, I had some 3D prints ready. I printed out several sizes, scaling the height to for various aesthetic tests.
This was my favorite one. It vaguely looks like cooking pot or a tortilla canister, but not *very* much. Those three rectangular ridges, parked at 120-degree angles, give it an unusual form
Now, it’s time to begin the more arduous project of mapping the cisterns themselves. And the tough part is still finishing the software that maps the cisterns into 3D space and exports them as an STL with some sort of binding support structure.
* I’ve only been able to locate 169 cisterns. Some reports state that there are 170 and others that there are 173 and 177.