Best Available Maps - Frequently Asked Questions


Question:       What is the purpose of the Best Available Floodplain Maps (BAM) being released by the Department of Water Resources (DWR)?

Response:     The Planning and Zoning Law requires a city or county general plan to include specified mandatory elements including the land use element identifying and reviewing areas covered by the general plan that are subject to flooding as identified by floodplain mapping prepared by the Federal Emergency Management Agency or the Department of Water Resources.  These maps provide currently available information.  They are subject to change as new or revised floodplain data is completed.

Question:       If the maps have no regulatory status, why is the State releasing them?

Response:     The provided information is a legislative requirement under Senate Bill 5 and is intended to ensure cities and counties have the best available flood risk data to support future flood planning needs.

Question:       How does the BAM differ from the Federal Emergency Management Agency (FEMA) regulatory floodplain maps?

Response:     The BAM are provided for informational purposes only and are intended to reflect current 100-, 200-, and 500-year event risks using the best available data.  FEMA regulatory maps have been prepared to support the National Flood Insurance Program (NFIP) and reflect only the 100-year event risk. 

Question:       What is the difference between the 100-year floodplain limits on these maps and the 100-year flood boundaries on the FEMA maps?

Response:     The 100-year floodplain limits on these maps are a composite of multiple 100-year floodplain mapping sources.  It is intended to show all currently identified areas at risk for a 100-year flood event including the FEMA’s 100-year floodplains. 

Question:       What criteria did the State use to develop the BAM, and are they different from those used by FEMA or the Corps?

Response:     The BAM are comprised of different engineering studies performed by FEMA, Corps, and DWR for assessment of potential 100-, 200-, and 500-year floodplain areas.  These studies are used for different planning and/or regulatory applications.  There are for the same frequency, however, they may use varied analytical and quality control criteria depending on the study type requirements.

Question:       If the BAM indicate a flood risk different from that indicated by the FEMA maps, will FEMA use these BAM in making future decisions regarding FEMA NFIP maps?

Response:     FEMA is currently implementing a nationwide program to modernize the NFIP.  FEMA would not directly adopt the BAM; however, the FEMA mapping process will likely consider and evaluate any additional data that the State has used to develop the BAM.

Question:       Will the BAM become replacements for current FEMA maps?

Response:     No.  The BAM are not regulatory maps.  They will simply incorporate the best available floodplain information from FEMA and other sources as it becomes available.

Question:       How can local agencies identify data sources from the BAM, especially where these new maps differ from existing FEMA floodplain maps?

Response:     Any floodplain areas shown beyond FEMA floodplain maps are based on documented studies.  The identification of these sources can be obtained from Floodplain Risk Management Branch web site (

Question:       Why does the BAM depict my city or county within a 100-year floodplain boundary when it has weathered multiple past events without damage?

Response:     This floodplain has been identified base on potential risk for a 100-year flood event.  The magnitude of this event may not have occurred or, because of adequate flood fighting at the time of past flood events, this area may have protected from flooding.

Question:       Do the BAM have any impact on future State flood risk liability?

Response:     Levee maintenance and the level of protection will be improved by adequate land use planning.  Awareness will reduce exposure to flooding for new structures and will promote increased protection for existing development.  It will also support identification of the need and requirement for flood insurance.  Yes, the BAM will impact future State liability.

Question:       Will my property values decrease as a result of the BAM placing me in a 100-year, 200-year, or 500-year floodplain?

Response:     It is not expected.  Identification of regulatory mapping and the requirements for flood insurance could possibly impact property value but that is a FEMA program, not a DWR program.

Question:       Why weren’t local agencies/organizations advised about this much earlier in the process?

Response:     This is not new information.  These are floodplains developed by past studies that were available to the public. 

Question:       What process is in place to refine the BAM maps based on input from local communities?

Response:     These will continually be updated.  As new information becomes available it will be incorporated on at least a quarterly basis.

Question:       What assistance will the State provide to local agencies in terms of holding public forums and explaining the BAM maps/impacts to residents?

Response:     Community conference calls have already been held to answer any questions concerning these maps.  DWR’s Floodplain Risk Management Branch web site provides a staff list of contacts for any additional questions/issues for the BAM maps and other mapping programs within DWR. (