Water and Wastewater System Disruptions

The following information comes from the multi-jurisdictional Local Hazard Mitigation Plan for the San Francisco Bay Area, Infrastructure Chapter, ABAG 2010.

The regional water and wastewater systems in the Bay Area are managed by a network of public special districts, city and county departments, and private companies. There are over 100 water retailers and wholesalers in the Bay Area. While most wastewater collection and treatment is handled by cities and counties, some special districts treat wastewater. ABAG estimates that there are 32,000 miles each of water and sewer distribution pipes in the Bay Area.

Some communities within the Bay region derive their urban, suburban and rural water supplies from groundwater and surface waters within the nine-county region (Napa River, Russian River, Guadalupe River, numerous creeks and springs). Others rely on groundwater and surface waters that are imported from watersheds and basins outside the region (including the Tuolumne, Mokelumne, Sacramento, San Joaquin and Eel River watersheds). The State of California Water Project and the U.S. Bureau of Reclamation Central Valley Project are large suppliers of water to the Bay region.

The Bay Area contains over 400 watersheds, including a portion of the Sacramento/San Joaquin watershed system. Water is distributed from these watersheds via a series of open and closed conveyances within the region, and inter-regionally. A significant amount of annual supply is impounded in 260 major reservoirs and behind numerous small check dams scattered throughout the region. 75% of the water supplies for the Bay Area are from water agencies that obtain all or part of their water either from aqueducts or canals passing through the Sacramento-San Joaquin Delta or by extracting water from the Delta.

Earthquake Hazards and the Bay Area Water and Wastewater Systems

Examining the locations of dams, water and wastewater treatment facilities, and pipeline networks that make up the water supply and wastewater collection system, shows earthquakes to be the greatest hazard. Because these systems have to be located in urban areas to serve those communities, their general hazard exposure is similar to that of the areas they serve.

The following table shows the percentage of water and wastewater system facilities and distribution pipelines exposed to earthquake-related hazards.

View exposure of pipelines by city or county.

Fault Rupture and the Bay Area Water and Wastewater Systems

When faults rupture and generate earthquakes, that rupture can extend to the surface, rupturing aqueducts and pipelines. Existing state law prohibits the construction of structures intended for human occupancy across the trace of an active fault. However, water aqueducts and pipelines cross these faults. For example, if the Hayward fault ruptures from San Pablo Bay to its southern end near the Santa Clara County border, fault surface rupture could severely damage the Hetch-Hetchy aqueducts, the EBMUD aqueducts, the South Bay aqueduct, and numerous local pipelines. Some dams are also on or near faults. In some cases, local roads have been intentionally placed astride faults as a land-use decision to avoid the placement of buildings astride the fault. When this occurs, the water and sewer pipelines are placed in this same alignment.

What Will Happen in a Future Earthquake?

In the 1989 Loma Prieta earthquake, the Bay Area experienced 507 water pipeline breaks or major leaks. An ABAG analysis indicated that pipelines subject to liquefaction and violent ground shaking were most likely to have broken or leaked.

ABAG has estimated that there could be 6,000 – 10,000 water pipeline breaks or major leaks in a future earthquake on the Hayward fault. (LHMP, ABAG 2010)

Bay Area residents have funded major improvements to the San Francisco PUC, East Bay Municipal Utility District (EBMUD), and Contra Costa Water District (CCWD) systems. EBMUD, CCWD, and Santa Clara Valley Water District (SCVWD) have installed, and SFPUC and Alameda County Water District are in the process of installing, shut-off valves on pipelines that cross faults and enable above ground portable water bypass lines to be rapidly installed.

Weather-Related Hazards and the Bay Area Water and Wastewater System

The Bay Area has historically had a mild Mediterranean climate characterized by mild rainy winters and dry summers. Flooding and landsliding occurred during the wet season, while wildfires and drought occurred in the dry season.

Climate change has been shown to exacerbate all of these hazards. Thus, the region can expect more flooding and landsliding due to a more abrupt runoff in the spring, as well as increased potential for wildfires any time of year and multi-year drought conditions. Some wastewater treatment facilities may be subject to the threat of sea level rise.

View exposure of these facilities by city or county.

Lifeline Interdependencies and Disaster Recovery

One of the main reasons for the interdependencies of infrastructure systems is that they tend to be geographically located in the same areas. For example, water, sewer, and natural gas pipelines tend to be under local roads. Communications and electrical cables are either located under those roads or adjacent to them. All have similar exposures to hazards that are related to serving the developed portions of the region.

In addition to geographic interdependencies, lifeline systems also have system interdependencies. Examples include the use of the transportation system to deliver water treatment chemicals to a water treatment facility and the short-term use of the electric power system to run pumps at that water treatment facility. Such interdependent analyses therefore need to address the length of time required to restore various services or interdependences to a level adequate for recovery. The length of time of a disruption increases the impacts. However, typically, doubling the time of disruption more than doubles the impacts. In addition, the disruption of one infrastructure system delays the recovery of other systems because the infrastructure systems are not available. Speeding the recovery of infrastructure systems is particularly critical.

Mitigation Resources

Be Sewer Smart! – helping the public cope with sewer disruptions

Multi-jurisdictional Local Hazard Mitigation Plan (LHMP) for the Bay Area, ABAG 2010

Water/wastewater agency annexes to LHMP

EBMUD seismic mitigation planning (ppt)

Water/wastewater Agencies Response Network (WARN) – water sector mutual aid

Last updated: 11.05.2014