How Safe Are Our Reservoirs?
by Nancy Wuerfel
Last month, readers were provided with a litany of proposals, promises, concerns and
questions about the Auxiliary Water Supply System (AWSS) extensions into the western
and southern neighborhoods to fight fires after a major earthquake.
The SF Board of Supervisors at the March 15, 2017 Government Oversight Committee
meeting requested that an independent consultant be engaged to report on the water
system, to assess the alternatives and to prepare a study of the comparative costs.
This report will be finished by the end of December, so the public discussion of
methods and projects will continue with a new analysis.
However, a critical part of this debate is missing: Where will the water
come from if a key reservoir fails as a result of an earthquake? Current plans
do contain multiple redundant water supply systems dedicated to firefighting
from separate sources through various delivery methods, but are these enough?
There is no separate analysis that identifies backup sources specific to replacing a large
quantity of firefighting water that floods out of any of the three very important
reservoirs as a result of damage from an earthquake – the Sunset, Sutro and University
This potential water loss is especially problematic if damage is done to the high capacity
Sunset Reservoir’s north or south basins, which store potable water intended to be
pumped into the AWSS through a plan that uses the reservoir for both drinking
water and firefighting.
What dedicated sources are there to replace the volume of water lost from
a damaged Sunset Reservoir basin? Will water from Lake Merced be enough? Should we
plan to install the necessary infrastructure near the ocean to facilitate the use of fire
boats to pump seawater into the AWSS to save the Sunset and Richmond districts
The city’s 2014 Hazard Mitigation Plan states, “The probability of a failure involving
dams or reservoirs located in or owned by San Francisco is unknown.” Also, the plan
concludes, “the exact extent of potential flood inundation due to reservoir failure in
San Francisco is unknown.”
The 2014 plan relies on maps drawn in the ’70s to calculate potential flood inundation.
These maps need to be updated to reflect current neighborhood changes and the many
improvements made to the city’s reservoirs.
On a brighter note, the Sunset, Sutro, and University Mound reservoirs are designated as
dams and are under the jurisdiction of the Division of Safety of Dams (DSOD). As such,
they are inspected annually by state inspectors to ensure the structural integrity
of the reservoirs remains within state and federal performance standards.
In addition, the SF Public Utilities Commission’s staff performs weekly visual monitoring
of the reservoirs’ structural integrity to ensure they continue to meet required state
standards. Regarding the Sunset Reservoir, SFPUC staff states: “Based on these
inspections, the reservoir has proved to be in good shape and meets
all required state and federal standards.”
But, will this be the status after an earthquake too?
The issue of fighting fires is a matter of having sufficient water available
and a delivery system in place to meet the demand. The reservoirs need to be
intact or fully backed up, otherwise what good are the pipes without water?
Nancy Wuerfel is a government fiscal analyst and served as a member of the Park,
Recreation Open Space Advisory Committee (PROSAC) for nine years.