safety element

The Safety Element is intended to prevent loss of life, to reduce injuries and property damage, and to minimize economic and social dislocation that may result from earthquakes, other geologic hazards, fires and flooding.  It seeks “to increase public awareness of geologic, fire and flooding hazards, and of available ways to avoid or mitigate the effects of these hazards.”  

The Safety Element surveys a variety of potential hazards, such as faulting, soil shaking, liquefaction, flooding, soil expansion and fire, and then generally assesses their respective degrees of risk in various areas of town.  By doing so, it strives to provide a sound basis for designating land uses that are appropriate to the geologic, fire and flooding risks of a proposed development site, and thereby “minimize the risk to human life from structures located in hazardous areas.”

The current version of the Safety Element was written and adopted in 2010 before we experienced the catastrophic wildfires that have plagued California since 2015, the increasingly deleterious effects of climate change, or the devastating coronavirus pandemic of 2020.  It is in urgent need of revision and updating in light of lessons learned from each of these calamities.

In particular, the Safety Element does not incorporate many of the lessons learned since 2010 from California’s recent experience with catastrophic wildfires.  It does not assess the topographic, climatic, seasonal and weather conditions that can accelerate and exacerbate the rapid spread of wildfire throughout a community, nor does it assess the way in which unsound land use policy and/or development can threaten the lives and property of neighboring property owners.  And finally, it does not consider how seismic events can cause and contribute to the rapid, uncontrolled proliferation and spread of fire.

Objectives.  The Safety Element clearly sets out its most important objectives:

• “To define the relative degree of risk in various parts of the planning area so that this information can be used as a guide for minimizing or avoiding risk for new construction and for risk abatement for existing development.

• “To minimize the risk to human life from structures located in hazardous areas.

• “To provide a basis for designating land uses that are appropriate to the geologic, fire and flooding risks in the planning area.

• “To ensure that facilities whose continued functioning is essential to society, and facilities needed in the event of emergency, are so located and designed that they will continue to function in the event of fire or natural disaster.

• “To facilitate post-disaster relief and recovery operations.

• “To increase public awareness of geologic, fire and flooding hazards, and of available ways to avoid or mitigate the effects of these hazards.”

Principles.  To achieve these objectives, the Safety Element also spells out a number of important principles, including:

• Land uses should be controlled to avoid exposure to risk in excess of the level generally acceptable to the community (“Acceptable Risk”).

• Development should be located, to the maximum extent feasible, to avoid areas which present high risk exposure.

• Development in hazardous areas should be limited to structures and improvements that would not threaten human life or cause substantial financial loss if damaged, or the development or site should be engineered to mitigate the hazard if possible without unduly disturbing the natural environment.

• High hazard areas should not be subdivided unless and until adequate mitigating measures are assured.

• Critical facilities, such as major transportation links, communications and utility lines and emergency shelters, should be located, designed and operated in a manner that maximizes their ability to remain functional after a disaster.

• New structures should be designed and constructed to withstand, within levels of acceptable risk, the hazards known to exist at their locations.

• The public should be made aware of hazards and measures that can be taken to protect their lives and property.  

The Safety Element focuses its greatest attention on the variety of different seismic risks confronting the town.

Faulting.  “Portola Valley is bisected by the San Andreas Fault Zone which is made of a number of individual fault traces along which movement has occurred at some time in the past.  Some of the traces of the San Andreas Fault Zone are considered to be active; some are of undefined activity; some are deemed to be inactive; and others are poorly defined or as yet are unrecognized and their activity is questionable.”

“The hazard associated with active fault traces is clear.  Any structure built across such a trace and subsequently offset by faulting would be in danger of collapse and constitute a threat to life.  Studies of the San Andreas Fault in California and other similar faults elsewhere in the world show that dislocations associated with faulting tend to be concentrated along relatively narrow traces.  In Portola Valley, however, a pattern of en echelon ground breakage has occurred along some of the San Andreas trace.  In these locations ground breakage consists of short ruptures on the order of 40 feet oriented obliquely to the general fault trend.  Also, a belt of disturbed ground several hundred feet wide or more, characterized by secondary fractures and cracks, ground lurching and warping may develop along traces of dislocation.”

The Safety Element states that the most detailed information regarding the description and location of the most recognizable active fault traces in Portola Valley is contained in the unpublished W.R. Dickinson, “Commentary and Reconnaissance Photogeologic Map of the San Andreas Rift Belt, Portola Valley, California.”   Unfortunately, the Safety Element does not publish the map and it is not available on the Town’s website or the Internet.

The San Andreas Fault Zone.  With respect to the San Andreas Fault Zone, the Safety Element states that traces “judged to be active and with significant potential for future displacement are shown with distinctive heavy lines on the Geologic Map of the Town.  The Town’s Geologic Map shows the following fault traces intersecting the Meadow Preserve adjacent to the location of the Neely agricultural building:

The Agricultural Building is located between two traces of the San Andreas Fault, on superficial alluvium soils susceptible to severe ground shaking and liquefaction during an earthquake.  

The Safety Element also points to California State mapping of the seismic hazards along the San Andreas Fault System.  The California Geological Service’s Seismic Hazard Zones maps the overlapping fault and liquefaction zone beneath and surrounding the Neely Agricultural building in the Meadow Preserve.

Dibblee’s map also provides a series of subsurface cross-sections passing immediately northwest (cross-section A) and southeast (cross-section B) of the Meadow Preserve.  These cross-sections depict the subsurface composition of soils surrounding the faults through the Meadow Preserve as well as the depths and angles of the faults.

The Jasper Ridge – Felt Lake Fault.  In addition to the San Andreas Fault Zone, the U.S. Geological Survey’s map of the town and its surrounding area for the National Geologic Map Database identifies other active faults traversing the town, including a fault between Jasper Ridge and Felt Lake crossing Westridge Drive and the Stanford Wedge.  The portion of Dibblee’s map of the Jasper Ridge – Felt Lake fault is shown below traversing Westridge Drive and the western edge of the proposed site for Stanford’s housing project.

Dibblee’s map also provides a series of cross sections passing immediately north of the Wedge (cross-section B) and south of Felt Lake (cross-section C) depicting the subsurface composition of soils surrounding the fault between Jasper Ridge and Felt Lake as well as the depth and angle of the fault.

Ground Shaking.  “The ground effects from seismic shaking in Portola Valley would vary with different underlying rock formations, soil conditions, and the amount of underground water present.  Those areas underlain by relatively thick, unconsolidated, water-soaked surficial sediments (such as some recent alluvial deposits) have a greater potential for damaging effects due to ground shaking than do areas of firm bedrock….  Surficial Materials are considered likely to respond more actively to an earthquake than Near-Bedrock Materials, which in turn, would respond more actively than Bedrock Materials.”

As the Town’s Geology Map shows, Stanford’s proposed housing site is comprised of surficial, alluvium deposits subject to the highest risk of ground shaking.

Ground Settlement.  “Ground settlement is the sinking of the surface of the land and is most commonly due to the compaction of unconsolidated granular sediments and soils.  The process of compaction can be accelerated by loading imperfectly compacted soils with buildings, excessive withdrawal of groundwater, or by ground shaking resulting from earthquakes.  “Seismically induced ground settlement or “shakedown” may occur very rapidly” and, particularly when aggravated by human or seismic processes, “may be unequally distributed over a small area with damaging effects to foundations or structures resting directly on the settled ground.” 

Soil Liquefaction.  Soil liquefaction occurs when certain water-saturated soils, subjected to intense shaking, temporarily lose their tensile strength and instead behave like a fluid.  “Soils most susceptible to liquefaction are saturated, well-sorted, poorly compacted fine sands and silts.”  The risk of liquefaction in localized areas along valley floors underlain by unconsolidated alluvium and a seasonally high-water table is considered relatively high.  The California Geological Service has mapped the areas of potential liquefaction, such as Stanford’s proposed housing site, which require further geologic investigation prior to any development. 

The green shaded area depicts areas “where historical occurrence of liquefaction, or local geological, geotechnical and ground water condition indicate a potential for permanent ground displacements such that mitigation as defined in Public Resources Code Section 2693 (c) would be required.”

Erosion and Sedimentation.  “Erosion occurs chiefly on steeper slopes in the upper reaches of drainage basins where runoff velocities are high.  Sedimentation, on the other hand, takes place mainly in the lower reaches of drainages where stream gradients and velocities are reduced.”  Although the Town has performed no detailed study, the Safety Element states that “surficial deposits of alluvium and slope wash as well as landslide deposits can be expected to be most susceptible to erosion.”

Fire Hazards.  In 2008 the Town engaged the Moritz Arboricultural Consulting firm to prepare a Fire Hazards Map depicting the relative risk of fire created by vegetation throughout the town.  The firm examined the types and extent of vegetation throughout the town and categorized the relative risk of fire in various areas of the town according to four classifications of risk:  highest fire risk (h+), high fire risk (h), moderate fire risk (m) and low fire risk (l). 

As classified by Moritz, the Stanford Wedge property is classified as (h+), among the highest fire risks in town.  As the Safety Element states, “[s]everal steep wooded canyons and steep slopes … are classified as the ‘highest’ risk.  These canyons are generally the steep back portions of lots where homes, often with wood roofs, are located higher on the properties.  Fires in these somewhat remote areas pose a major threat and warrant coordinated actions by property owners bordering the canyons.”

Notably, the Moritz map did not consider or address important additional risk factors that only compound the threat of fire created by development in the Stanford Wedge, including water supply, accessibility, land slope and flammability of surrounding structures.

Safety Policies 

In general, the Safety Element calls for prudent consideration and investigation of each of the various categories of hazard identified in the plan whenever development is proposed.   In known or suspected hazardous areas, further investigation of geological or other site specific risks should be undertaken.   All mapped fault lines should be considered as active faults unless and until evidence to the contrary is developed in the field.  Appropriate geological investigations of fault traces other than the San Andreas Fault should be made and reviewed in connection with any application for construction of buildings for human occupancy, site development, or subdivisions.  So too with ground shaking hazards, landslide, ground settlement, liquefaction, erosion and sedimentation.

With respect to fire hazards, the Safety Element states that buildings for human occupancy should not be constructed in areas, such as the Stanford Wedge, having the highest fire risk unless it is demonstrated that mitigation measures will be taken to reduce the fire risk to an acceptable level.  In high fire risk areas, proposed subdivision projects should provide the Planning Commission a study that addresses at least a description of the risk and factors contributing to the risk, actions that should be taken to reduce the risk to an acceptable degree, the costs and means of providing fire protection to the subdivision, and an indication of who will pay the costs involved and who will benefit or be harmed by such measures.  

The Safety element pointedly notes that just because a risk can be mitigated does not necessarily mean that it should be mitigated.

“Many of the measures that might be taken to mitigate hazards cited in this element could produce results in conflict with other elements of the general plan.  Just because natural hazards can be mitigated does not mean that in all cases they should be, especially if such mitigation would produce results that are in conflict with the conservation element, the land use element, the open space element, or other sections of the general plan.” 

The Safety Element also calls on the Town to establish a public information program utilizing the Moritz report to inform residents of the town’s fire hazards and how they can be reduced.  Unfortunately, 10 years after the Safety Element was written, and 12 years after the Moritz map was prepared, the Town has still initiated no program to use the map or other information sources to inform or educate the Town’s residents regarding the extreme risks of wildfire in Portola Valley.  Indeed, the Town has not even published the Mortiz map on its website. 

The Safety Element also calls on the Town to prepare and implement an Emergency plan to protect persons and property in the town in the event of an emergency, and to provide for the coordination of emergency services of the town with other public agencies, such as the Woodside Protection District and CalFire.  The Safety Element specifically calls for:

• “The establishment and maintenance of an emergency operations center is a high priority of the town.”

• “Routine emergency exercises should be conducted periodically to continually test the Emergency Plan and make improvements in the system.”

• “Major town-wide emergency exercises should be conducted based on carefully prepared scenarios of the major events likely to face the town, most notably wildland fires and earthquakes.”

Ten years later, many of these important policies have not been fully implemented.  The Town has established an emergency operations center and developed procedures to staff and operate the center in emergencies. Few residents are aware of or familiar with the functions or capabilities of the center, or how to access and use them. Information regarding the center can be accessed by searching the Town’s website for “emergency operations center” or by clicking this link: EOC.

While the Woodside Fire and Protection District has prepared and provided a proposed Emergency Evacuation Plan for the town, the plan has not been implemented, widely publicized or practiced on a Town-wide basis.

The Woodside Fire Protection District has developed a neighborhood self-help program — called WPV-Ready or Citizens Emergency Response Preparedness Program (CERPP) or PV-Ready — for Portola Valley and Woodside that divides Portola Valley into 9 district neighborhoods with volunteer leaders for emergency preparation and response. Information regarding the program can be accessed on the Fire Protection District’s WPV-Ready or on the Town’s website under the “Residents” tab on the CERPP Response Team page. In addition, the Town’s website provides emergency preparedness information and links on its website under the Residents tab.

The Town and various neighborhoods within town have periodically conducted small scale drills and exercises for the emergency operations center and neighborhood communication and response. The Town has yet to conduct any town-wide exercise or drill to test procedures for town-wide emergency evacuation in case of wildfire or earthquake.

In April 2019 the Town created an ad hoc Wildfire Preparedness Committee to advise the Town Council.  The ad hoc Committee has since met several times and has recommended various vegetation removal initiatives and outreach programs as well as certain infrastructure improvements.

Much has been done by Town staff and many dedicated residents working on a volunteer basis largely at a neighborhood scale.  PVNU believes that more can and should be done on a Town-wide basis, particularly in light of the learning gained from California’s many recent catastrophic wildfires.

Going Forward. 

First, as the General Plan provides, the Town should promptly address the enormous challenges of an urgent Town-wide evacuation by organizing and conducting major Town-wide emergency evacuation drills.  The challenges entailed in organizing, communicating, executing and directing such a large scale evacuation of all Town residents and livestock on an urgent basis are daunting to say the least.  Unless and until we confront and address those challenges on a Town-wide scale in actual drills, we are simply not prepared to deal with any realistic wildfire or earthquake scenario.

Second, the General Plan’s Safety element should be implemented and updated to incorporate the lessons learned from California’s most recent experiences with catastrophic wildfires in communities like Portola Valley.  The Safety element should identify the principal causes of wildfires in Portola Valley’s ecosystems, define the topographical and fuel conditions that constitute Very High and High Fire Hazard zones within Town, revise the Town’s land use policies and ordinances to enhance the safety of development in Very High and High Fire Hazard zones within Town, and detail the Town’s emergency response procedures and resources.  The 2008 Moritz Fuel Hazard Assessment Study and Map provide excellent building blocks on which to develop the necessary policies and revisions to the Safety element.

In particular, the General Plan’s Safety element should incorporate the lessons learned since 2010 from California’s recent experience with catastrophic wildfires. 

• It should assess the local topographic, climatic, seasonal and weather conditions that can accelerate and exacerbate the rapid spread of wildfire throughout a community;

• It should assess the way in which unsound land use policy and/or development can threaten the lives and property of neighboring property owners as well as those within a proposed development;

• It should consider how seismic events can cause and contribute to the rapid, uncontrolled proliferation and spread of fire through the disruption of water supplies or electrical and gas service;

• It should assess the fire hazard that existing gas, electric or solar utilities pose within town and implement appropriate steps to reduce such hazards;

• It should structure and provide for implementation of suitable hazard and risk assessments in all land use decisions;

• It should provide for community-wide programs to restore healthy forests and reduce flammable vegetation and other fuels through ecological thinning to mitigate the risk of wildfire ignition and spread in the community; and

• It should address the potential need to evacuate the town and provide comprehensive procedures to timely inform residents of evacuation orders, safe routes of escape to implement such orders, and appropriate procedures to organize and administer post-evacuation relief and recovery activities.

The day after a wildfire sweeps through town is far too late to get started.  The Town needs to realign its priorities and act on them now.

Third, the Town should adopt a new wildfire safety ordinance that:

• Applies the lessons learned from the Moritz Report and California’s most recent catastrophic wildfires to define and establish Very High and High Fire Risk zones within Town and adopt wildfire-safe land use and building standards for those zones, much like the Town’s seismic safety policies and ordinances adopted 50 years ago;

• Amends the fire ordinance to empower the Woodside Fire Protection District to require the removal of excessive ladder fuels and dead vegetation from any property within Very High and High Fire Hazard zones in Portola Valley; and

• Establishes a Public Safety Officer in Town government to implement and enforce the wildfire prevention, safety and emergency preparedness policies and requirements of the Town’s General Plan and municipal code.