Cole Valley Alley Solves Cistern Mystery
CVA asks the perennial question, “what’s up with the circular brick patterns in the middle of San Francisco streets?” Here’s the geometry of mystery at Frederick & Shrader:
and 13th & Folsom:
“My curiosity was piqued. What do they mean? Why are they there? Are they the remnants of an ancient civilization, a decorative flare from a bygone era of well funded city government, or simply the remains of an old cobblestone street?”
CVA quickly passed the SF history/infrastructure rite of passage and discovered they are SFFD water cisterns. But what was impressive was the route they took to get this information. They emailed the SFDPW and got a great response, including the original 1909 plans for the 75,000 gallon cistern on Frederick & Shrader:
(bonus: awesome fonts!)
The also received details on how the brick circle is to be laid in a bed of supporting concrete:
(For about 10 minutes I puzzled over this diagram, misreading inches for feet and interpreting it as a cross section of the entire structure. I couldn’t for the life of me figure out how the damn manhole was floating over the cistern. But I digress.)
The bricking rules are very specific (and oddly comforting):
Glad to see the partial circles are intentional.
These upgraded and reinforced cisterns were a big part of the redesign of the fire response system after 1906 — the cisterns were to be a source of water of last resort if the water mains were destroyed. They had been around since the 1850s — in fact you can see them in the 1853 and 1859 Coast Survey Maps:
1853, around Dupont & Washington:
And 1859, around Sansome & Pine.
Anyway, a warm welcome to Cole Valley Alley and their infrastructuriosity!