Flood Hazard

What to Do During a Flood Event

When flooding is occurring, residents should immediately monitor official local alerts and weather updates and follow evacuation instructions as soon as they are issued. In Humboldt County, emergency notifications are provided through Humboldt ALERT and weather updates and flood warnings are issued by the National Weather Service in Eureka. You can also monitor the Office of Emergency Services Current Emergencies page for more information.

Travel during flooding is extremely dangerous, and people should never drive or walk through floodwater. Even shallow water can sweep away vehicles or hide washed-out roads, debris, or open culverts. The National Weather Service’s “Turn Around, Don’t Drown” guidance applies in all flood situations and is especially relevant on rural and low-lying roads common throughout our County. Before traveling, residents should check current road conditions and closures through Caltrans QuickMap for state highways and the County Public Works Road Conditions page for county roads.

Flooding often brings secondary hazards that can be just as dangerous as the water itself. Downed power lines, damaged gas lines, unstable structures, and contaminated floodwater pose serious risks. People should stay away from standing water near electrical equipment and never enter buildings surrounded by water unless authorities say it is safe. Floodwater may contain sewage, fuel, agricultural runoff, or sharp debris, and contact should be avoided whenever possible.

During recovery, protecting health is a priority. Flooded buildings should be dried out as quickly as possible to reduce mold growth, and water-damaged porous materials that cannot be thoroughly cleaned should be removed. Food and drinking water should not be used if there is any chance they were exposed to floodwater, and residents should follow public health guidance regarding water safety. Documenting damage with photos or videos before cleanup, if it can be done safely, can help with insurance claims and disaster assistance. For more information about safety during flood events see the ready.gov Floods webpage and the National Weather Service Flood Safety Tips and Resources.

Development in the Flood Zone

Here's how these regulations work:

1. Flood Maps: FEMA develops Flood Insurance Rate Maps (FIRMs) that show flood hazard areas, known as Special Flood Hazard Areas (SFHAs). These maps outline different flood risk zones within a community, indicating the likelihood of flooding, from high-risk areas to moderate- and low-risk areas. The different SFHA zones are shown below.
   • Zone A: Areas with a 1% annual chance of flooding and a 26% chance of flooding over the life of a 30‐year mortgage. Because detailed analyses are not performed for such areas; no depths or base flood elevations are shown within these zones.
   • A1-A30: These are known as numbered A Zones (e.g., A7 or A14). This is the base floodplain where the FIRM shows a BFE (old format).
   • Zone AE: The base floodplain where base flood elevations are provided. AE Zones are now used on new format FIRMs instead of A1‐A30 Zones.
   • Zone AH: Areas with a 1% annual chance of shallow flooding, usually in the form of a pond, with an average depth ranging from 1 to 3 feet. These areas have a 26% chance of flooding over the life of a 30‐year mortgage. Base flood elevations derived from detailed analyses are shown at selected intervals within these zones.
   • Zone AO: River or stream flood hazard areas, and areas with a 1% or greater chance of shallow flooding each year, usually in the form of sheet flow, with an average depth ranging from 1 to 3 feet. These areas have a 26% chance of flooding over the life of a 30‐year mortgage. Average flood depths derived from detailed analyses are shown within these zones.
   • Zone AR: Areas with a temporarily increased flood risk due to the building or restoration of a flood control system (such as a levee or a dam). Mandatory flood insurance purchase requirements will apply, but rates will not exceed the rates for unnumbered A zones if the structure is built or restored in compliance with Zone AR floodplain management regulations.
   • Zone B and X (Shaded): Area of moderate flood hazard, usually the area between the limits of the 100‐ year and 500‐year floods. B Zones are also used to designate base floodplains of lesser hazards, such as areas protected by levees from 100‐year flood, or shallow flooding areas with average depths of less than one foot or drainage areas less than 1 square mile.
   • Zone C or X (Unshaded): Area of minimal flood hazard, usually depicted on FIRMs as above the 500‐year flood level. Zone C may have ponding and local drainage problems that don't warrant a detailed study or designation as base floodplain. Zone X is the area determined to be outside the 500‐year flood and protected by levee from 100‐ year flood.
   • Zone D: Areas with possible but undetermined flood hazards. No flood hazard analysis has been conducted. Flood insurance rates are commensurate with the uncertainty of the flood risk.
   • Zone V: Coastal areas with a 1% or greater chance of flooding and an additional hazard associated with storm waves. These areas have a 26% chance of flooding over the life of a 30‐year mortgage. No base flood elevations are shown within these zones.
   • Zone VE and V1-V30: Coastal areas with a 1% or greater chance of flooding and an additional hazard associated with storm waves. These areas have a 26% chance of flooding over the life of a 30‐year mortgage. Base flood elevations derived from detailed analyses are shown at selected intervals within these zones.
2. Building Standards: Buildings located in SFHAs must meet certain construction standards to minimize their vulnerability to flood damage (see Humboldt County Code 335-1). For example, new buildings must be elevated above the base flood elevation - the level that has a 1% chance of being equaled or exceeded in any given year. Additional requirements include using construction materials and methods to prevent flood damage, ensuring structures are anchored against movement by floodwaters, and ensuring utilities are flood proofed. These standards are further outlined by the FEMA technical bulletins.
3. Community Participation: Communities that participate in the NFIP are required to adopt and enforce floodplain management ordinances that meet or exceed FEMA requirements. In return, the NFIP makes federally backed flood insurance available to homeowners, renters, and business owners in these communities.
4. Insurance: For properties within high-risk areas (known as Special Flood Hazard Areas), there's a federal requirement for flood insurance if the property has a mortgage backed by a federal agency (like FHA, VA, USDA, etc.). While not federally required for properties in moderate- to low-risk areas, flood insurance is recommended and available for these properties as well.

To ensure compliance with these regulations and ensure Humboldt County residents continue to have access to flood insurance, the Building Division requires new development in SFHAs to be elevated 1ft above base-flood elevation or be flood-proofed. Both methods require a Flood Elevation Certificate or a Floodproofing Certificate (see Construction Documents) to establish a base-flood elevation.

Note that special requirements apply to grading in an SFHA (see Fill in Flood Zone handout), greenhouse pole structures in an SFHA (see Ag-Exempt Construction Documents handout), and additions/remodels to existing structures in an SFHA (see Substantial Improvements in the Flood Zone handout).