Floodplain Management

Public Works Employee managing a flood zone

The San Francisquito Creek Joint Powers Authority (SFCJPA) and the City of Palo Alto invite residents of Palo Alto, East Palo Alto, and Menlo Park to a community meeting regarding the latest changes to the National Flood Insurance Program (NFIP) and flood insurance rates.  A new law approved in 2012 and recently modified makes significant changes to flood insurance rates and policies that affect residents and businesses in the FEMA-designated floodplain.

ATTENTION: The Federal Emergency Management Agency has issued a letter revalidating Letters of Map Amendment (LOMAs)(PDF, 805KB) in conjunction with the issuance of the new Flood Insurance Rate Map, effective May 18, 2009.  If your lender or insurance agent questions the validity of your LOMA because of the issuance of the new flood map, you should send a copy of this letter to document that the LOMA has been re-validated.  If you have questions or need further information, please visit the City’s Development Center at 285 Hamilton Avenue or contact Public Works engineering at (650) 329-2151.

In order to make flood insurance available to residents and businesses throughout the United States, Congress created the National Flood Insurance Program (NFIP) in 1968, with the government acting as the insurance underwriter.  Flood insurance is made available on a community basis once a community has joined the NFIP and agreed to enforce a set of federally-based standard floodplain management regulations through adoption of a local ordinance.  The floodplain management ordinance regulates land development within the designated floodplain in order to minimize the risk of flood damages.  The NFIP was placed under the jurisdiction of the Federal Emergency Management Agency (FEMA) and its Flood Insurance Administration (FIA).

Palo Alto joined the NFIP in the late 1970s, and FEMA/FIA issued the first Flood Insurance Rate Map (FIRM) for the City of Palo Alto in 1980.  The FIRM designates the flood zone for properties throughout the City and identifies those properties that are within the Special Flood Hazard Area (SFHA).  Properties in the SFHA are projected to be subject to flooding in the event of the 1% (100-year) flood event and are subject to the City’s Flood Hazard Regulations (Palo Alto Municipal Code Chapter 16.52).

Letters of Map Amendment (LOMA) / Letters of Map Revision (LOMR)

The Federal Emergency Management Agency (FEMA) issues Flood Insurance Rate Maps (FIRM) that designate the flood risk for properties throughout a community.  The FIRM designates the flood zone for properties and identifies those properties that are within the Special Flood Hazard Area (SFHA).  Properties in the SFHA are projected to be subject to flooding in the event of the 1% (100-year) flood event and are subject to the City’s Flood Hazard Regulations (Palo Alto Municipal Code Chapter 16.52).  The FIRM is developed at a macroscopic level and cannot distinguish local fluctuations in ground elevations that may change the flood risk to an individual land parcel.  Therefore, FEMA has a map change procedure that allows individual property owners to request a change to the flood zone designation of their parcel based on site-specific topographic information.  The tools of this program are known as Letters of Map Amendment (LOMAs) and Letters of Map Revision (LOMRs).  LOMAs and LOMRs have the effect of removing either a structure, a portion of a property, or an entire property from a Special Flood Hazard Area (SFHA), based on the elevation of the ground.  In effect, the applicant must prove to FEMA's satisfaction that their structure is located on ground high enough that the structure will be on its own little "island" during the 1% flood event (also known as the Base Flood).  The basic difference between a LOMA and a LOMR is that a LOMR is based on a ground elevation created by the addition of fill to the property since the date of the community’s first FIRM (February 15, 1980, for Palo Alto), whereas a LOMA is based on original grades.

Please note that floor elevation is not a factor in removing a structure from the SFHA -- only the appropriate ground elevation is relevant.

FEMA designates the following categories of LOMAs and LOMRs:

Letter of Map Amendment (LOMA):  FEMA verifies that applicant's land, or at least the land immediately adjacent to the structure, is high enough to be above the Base Flood Elevation (BFE).

  • Conditional Letter of Map Amendment (CLOMA):  Same as LOMA, but issued in advance of construction.  When construction is complete, appropriate as-built date must be supplied to FEMA for a permanent LOMA to be issued.
  • Letter of Map Revision Based on Fill (LOMR-F):  Similar to a LOMA, but based on fill added since the first FIRM date.  LOMRs require that the elevation of the lowest floor, including a basement, be above the Base Flood Elevation.
  • Conditional Letter of Map Revision Based on Fill (CLOMR-F):  An advance LOMR, prior to placement of fill; as-built information must be supplied at completion of construction for issuance of a permanent LOMR.
  • Letter of Map Revision (LOMR) and Conditional Letter of Map Revision (CLOMR): Used for larger projects involving fill where more general flood plain boundary changes might be involved. These are not usually applicable to individual small property owners.
  • FEMA will require a number of documents to be submitted as part of the application for a LOMA or LOMR.  Among these documents may be the following:
    • Recorded plat map or property deed (available from the Santa Clara County Recorder's Office).
    • Photocopy of the Flood Insurance Rate Map panel (available at the Development Center).
    • FEMA Property Information form (to be completed by the property owner).
    • FEMA Elevation Information form (to be completed by Licensed Surveyor or Registered Professional Engineer).
    • FEMA Summary of Elevations form (used when more than one lot is involved; to be completed by Licensed Surveyor or Registered Professional Engineer).
    • FEMA Certification of Fill Compaction (for LOMR applications; to be completed by Registered Professional Engineer).
    • FEMA Community Acknowledgement of Requests Involving Fill (for LOMR applications; completed by City of Palo Alto Public Works Engineering).

It will be necessary to hire a Licensed Surveyor or Registered Professional Engineer to provide some of the documents required for a LOMA/LOMR application.  There are up-front FEMA charges for certain types of applications, although there is currently no fee for a single-lot LOMA.  The LOMA/LOMR forms are available from FEMA online.

Once a LOMA or LOMR has been obtained, the applicant is relieved of the federal requirement that loans using the structure as collateral be protected by flood insurance, and a refund can be gotten for some current flood insurance premiums paid.  It must be remembered, though, that a LOMA/LOMR only "removes" a structure or property from the 1% flood area -- there is still some remaining risk of flood.  For instance, the structure may still be flooded in an event larger than the 1% event, and a lender may still consider it prudent to require flood insurance.  If the lender still requires flood insurance, however, the premiums will be much lower than before issuance of the LOMA/LOMR.

Once a LOMA or LOMR has been obtained for a property, that property is no longer subject to the special building regulations contained in Palo Alto Municipal Code Chapter 16.52.  Although LOMAs/LOMRs are issued by FEMA directly to the property owner and they are not official City documents, the City also receives a copy of these documents.  The City keeps an active file of all LOMAs/LOMRs received from FEMA.  For copies of LOMAs/LOMRs, please visit the City’s Development Center at 285 Hamilton Avenue or contact Public Works Engineering at 650-329-2151.

LOMAs and LOMRs that remove an existing structure from the SFHA are invalidated once the footprint of the structure is enlarged.  In all cases, LOMAs and LOMRs are only valid until the next revision of the FIRM is published, unless they are revalidated by FEMA.  If an existing LOMA/LOMR is invalidated, it will then be necessary for the property owner to ask for a replacement of the LOMA/LOMR based on a new application.  If the revised FIRM or expanded structure footprint does not create a change in the flood conditions for the property, a new LOMA/LOMR will normally be issued. Typically FEMA issues a blanket letter revalidating a list of LOMAs and LOMRs that are considered to be valid in conjunction with the issuance of a revised FIRM.  If you have a LOMA or LOMR and are uncertain as to its validity after a map update, please visit the City’s Development Center at 285 Hamilton Avenue or contact Public Works Engineering at 650-329-2151.

View the May 18, 2009 LOMA Recertification Letter.(PDF, 805KB)

San Francisquito Creek Joint Powers Authority

The City works with neighboring jurisdictions through the San Francisquito Creek Joint Powers Authority (SFCJPA) to address community concerns regarding flooding and environmental preservation on San Francisquito Creek.

The San Francisquito Creek SFCJPA is an agency empowered to protect and maintain the 14-mile San Francisquito Creek and its 45 square-mile watershed. The SFCJPA was created through the adoption of a joint powers agreement by the member agencies on May 18, 1999.

The SFCJPA strives to accomplish the following goals:

  • To facilitate and perform bank stabilization, channel clearing, and   other Creek maintenance.
  • To plan flood control measures for the San Francisquito Creek watershed.
  • To take actions necessary to preserve and enhance environmental values and instream uses of San Francisquito Creek.
  • To coordinate emergency mitigation and response activities relating to San Francisquito Creek.
  • To make recommendations to Member Entities for funding and alternatives for long-term flood control for Member Entity consideration.

Flood Insurance Rate Maps (FIRM) and Panels

The FIRM for the City of Palo Alto is broken down into multiple map panels.  The City of Palo Alto has been assigned the Community Number 060348, which is a unique identifier.  When identifying the FIRM map panel for a particular property, the complete map designation includes the Community Number, the Panel Number, and a letter indicating the map revision level.  Thus, a given parcel of land might be on FIRM 060348-0010H.  At this time all Palo Alto FIRM panels are at revision level H, indicating a revision date of May 18, 2009.

Each of the issued panels displays a portion of the city at a scale of 1" = 500', showing the boundaries of the various flood zones.  As might be expected, the scale is quite small and it is frequently difficult to determine the exact location of a flood zone boundary with respect to a given parcel of land, particularly if that parcel happens to lie on or near the boundary.  Public Works Engineering staff at the City’s Development Center, located at 285 Hamilton Avenue, can assist with the identification of the correct flood zone designation for a specific parcel.

Effective May 18, 2009, FEMA issued a new digital FIRM for the City of Palo Alto and the rest of Santa Clara County.  As of this date, the older version of the FIRM can no longer be used to identify the flood zone designation of properties in the City of Palo Alto.  The new FIRM is primarily a conversion of the existing paper-based FIRM to a digitally-based product.  As a result of the conversion, no additional properties were added to or removed from the Special Flood Hazard Area.  The conversion of the FIRM to digital format also included the conversion of the vertical datum of the mapping and the Base Flood Elevations from the National Geodetic Vertical Datum of 1929 (NGVD29) to the North American Vertical Datum of 1988 (NAVD88).

Flood Zone Look Up

The entire city of Palo Alto is in a flood zone of one kind or another. But most of the city is in an "X" zone, which the Federal Emergency Management Agency (FEMA) describes as an area either lying outside the so called 100 year flood limit and inside the 500 year flood limit, or as lying within the 100 year flood limit but shallow enough to not represent a special hazard. The remainder of the city lies within Special Flood Hazard Areas (SFHA), which, roughly speaking, means the area of special hazard from a so-called "100 year flood". Find out which flood zone your residence is in by using the parcel report request.

Request a Parcel Report

Flood Zone Descriptions

Flood Zone Descriptions: Zone A

Zone A is a designation for properties that are flood-prone in the event of a 100-year flood, but for which there is insufficient data available to establish a base flood elevation or a flooding depth. Several properties near San Francisquito Creek were mapped on the Flood Insurance Rate Maps as Zone A following the 1998 flood. These properties were subjected to flooding during the 1998 flood even though FEMA's hydrologic models did not predict such flooding.

Flood Zone Descriptions: Zone AE 10.5

There's only one such zone in Palo Alto. Flooding in the AE Zone is due to potential overtopping of the Bayfront levees in the event of an extremely high tide, particularly one that might be associated with a storm front.

This large zone is roughly bounded on the north by Embarcadero Road and on the south by the Mountain View city limits and includes everything easterly from roughly Middlefield, Ross and Louis Roads to San Francisco Bay. Originally, most of this area was tidal marsh and wetlands, but many years ago levees were built in the Baylands to drain the wetlands and allow the development of eastern Palo Alto. Because the levees lack required freeboard (additional height above the estimated high water level) and were not constructed in accordance with current engineering standards, FEMA does not consider these levees to be adequate protection from a high tide event that has a one percent (100-year) probability of occurring. The Flood Insurance Rate Maps were prepared under the assumption that the levees will overtop or fail and that the area in the AE 10.5 Zone will be flooded by tidal water to an elevation of ten and one-half feet above sea level (which is not the same as a depth of ten and one-half feet). Much of the residential area immediately west of the Bayshore Freeway is at only about six feet above sea level, meaning that the 100-year flood would reach a height of up to five feet above the ground.

If your property is near Greer Park, it may also be subject to flooding from San Francisquito Creek (see ZONE AH).

Flood Zone Descriptions: Zone A0

The A0 Zone involves shallow "sheet-flow" of between one and three feet depth from an overflowing creek.  There are a few small areas of localized A0 flooding in the City of Palo Alto adjacent to Matadero Creek near Hillview Avenue.

Flood Zone Descriptions: Zone AH

AH Zones are areas of fairly shallow flooding of less than three feet depth. The flooding source of the AH Zones in Palo Alto is overflow from local creeks. The Base Flood Elevation in these areas is expressed as an elevation above sea level.

The largest AH Zone results from overflow from San Francisquito Creek. FEMA's hydraulic models predict creek overtopping in the vicinity of Middlefield Road and Chaucer Street in the event of a one percent (100-year) flood. The overflow water flows downhill (one of the characteristics of Palo Alto's creeks is that their banks are actually higher than the adjacent land so that creek overflow water flows away from its source) and the Base Flood Elevation levels are shown by surface contour lines on the flood maps; the Base Flood Elevation for individual properties must be determined by interpolation. The creek overflow water is expected to flow towards the Embarcadero Road/Oregon Expressway/Bayshore Freeway interchange, and then over the Oregon Expressway and through the Greer Park area.

Because the Greer Park area is also subject to more severe flooding from the Bay, this area is designated as "Zone AE (El. 10.5)" on the flood maps.

The AH Zone was remapped following the February 1998 flood event. During that event, San Francisquito Creek overtopped its banks at multiple locations between Middlefield Road and the Bay, leading to widespread flooding. The San Francisquito Creek Joint Powers Authority (JPA) and its member agencies (Palo Alto, Menlo Park, East Palo Alto, the Santa Clara Valley Water District, and the San Mateo County Flood Control District) are in the process of developing a plan to address the risk of flooding from San Francisquito Creek.

Flood Zone Descriptions: Zone ACr

Palo Alto is traversed by several creeks. Obviously, these creeks carry rainfall runoff and so, by definition, are flooded after virtually any significant rainfall. The channels, then, are definitely Special Flood Hazard Areas. Where a 100-year flow in the channel would not overflow the banks, FEMA notes this on the flood maps as "ZONE A CONTAINED IN CHANNEL". Even if your land actually extends into the creek channel, you are not affected by the construction and insurance requirements unless your structure actually lies at least partly within the creek channel. Still, if your property does extend into a creek, it can sometimes be a bit difficult to convince a lender that you don't have to have flood insurance. And, if you're that close to a creek, it might not be a bad idea to carry flood insurance in any case.

Flood Zone Descriptions: Flood Zone X

All of Palo Alto that is not in a Special Flood Hazard Area is in "ZONE X", which is described as an area of moderate risk of flooding (roughly speaking, outside the 100-year flood but inside the 500-year flood limits), or, for A0 zones, where the 100-year flood will be less than a foot deep. Thus, all of Palo Alto has been determined to be subject to some risk of flooding, and it is inaccurate to say that a given property is "not in a flood zone" simply because it is not in a Special Flood Hazard Area.

The special floodplain construction rules are not applicable to structures in an "X" Zone, and federal regulations do not require that flood insurance be purchased to protect an equity loan on structures in an "X" Zone. But flood insurance is available for structures in "X" zones, and at rather attractive prices. FEMA states that some one-third of its claims payments for flood damage are for structures that are not within a Special Flood Hazard Area.

A structure can be removed from a Special Flood Hazard Area and changed to an "X" Zone designation by means of a FEMA-issued Letter of Map Amendment or Letter of Map Revision (LOMA or LOMR). For addresses where this has been done, the flood zone is designated as "X" (with the notation "LOMA" or "LOMR" in the comment field) in the look-up lists on this website.