Yavapai County Flood Control District

What is the difference between Floodway and Flood Fringe?

There are two delineations within the boundary of the 100 year floodplain/Base Flood known as Floodway and Flood Fringe.

Floodways are designated and mapped through detailed engineering studies. Mapped Floodways includes the channel of a river/watercourse and adjacent land areas which in an unobstructed condition can discharge a 100 year flood/Base Flood without any increase in water surface elevations.

The area between the floodway boundary and limit of the 100 year floodplain is termed Flood Fringe. The Flood Fringe encompasses the portion of this floodplain that could be completely obstructed without increasing the water surface elevation of a 100 year flood event more than 1 foot at any point.

Am I in a floodplain?

Email your parcel information to the Flood Control District for a Flood Status Report or call our Flood Status line at (928) 771-3196 and a report can be mailed.

What is a 100 year flood?

The term 100 year flood is misleading, most think it is a flood event which occurs only once in a 100 year time span.  Rather, it is a flood elevation that has a 1% chance of being equaled or exceeded each year. Thus, the 100 year flood could occur more than once in a relatively short period of time

The 100 year flood, which is the standard used by most Federal and State agencies, is used by the National Flood Insurance Program NFIP as the standard for floodplain management and to determine the need for flood insurance.

A structure located in a 100 year floodplain has a 26% chance of suffering flood damage during the term of a 30 year mortgage, and a greater chance of being damaged by a flood than by fire.


What is the 80 acre Drainage Policy?

On April 9, 1990, the Board of Directors for the Yavapai County Flood Control District adopted the following policy regarding watercourses with a tributary drainage area less than 80 acres:
“Violations or possible violation in a watercourse with a tributary drainage base area of less than 80 acres at the point of the violation or possible violation shall be considered as minor in nature since they do not pose a significant potential for loss of life and property and as such are not subject to enforcement actions by the District. The normal method of determining tributary drainage basins shall be delineation on a USGS 1″ = 2000′ scale topographic map. Not withstanding the above, the District Ordinance shall be strictly enforced within the District delineated areas of special flood hazard and within subdivisions and other developments where areas of special flood hazard were or will be delineated under District requirements as a condition of approval.”

In general terms, the policy means that the District will not require conformance with the District Ordinance when the tributary drainage area at the point of the potential violation is less than 80 acres. This policy does not relieve property owners from potential liability resulting from watercourse alterations.  The 80 acre drainage policy does not apply to the review and approval of new subdivisions, use permits, zone changes and related items.  For more specific information regarding this policy, contact the District office.

What is the regulatory elevation?

The Federal Emergency Management Agency requirement for building structures in flood hazard areas is that the floor of the lowest habitable enclosure must be elevated to or above the base flood elevation (BFE).  The BFE is based on the floodplain delineation for the-year peak runoff event.

In order to minimize potential damage to residential structures in flood hazard areas the State and Flood Control District requires an additional foot of free board of above the BFE, which is referred as the Regulatory Flood Elevation.

Do I need a registered engineer to prepare my building permit plans?

An Arizona registered engineer is needed for residential structures Building Permit Checklist Requiring Civil Engineering  ) constructed in floodways, in flood fringe areas with depths of flow typically greater than 2 feet, approximate Zone A study area, areas impacted by watercourse with drainage areas greater than 80 acres, and for most commercial developments (Commercial Building Permit Requirement Checklist ).  For structures located in FEMA or Yavapai County flood hazard areas an Elevation of Floodplain Property Form  will need to be completed by an Arizona Registered Land Surveyor.  In most cases, the engineering requirements are site specific.  Call the Flood Control District with the parcel number and an idea of where the structure will be located on the property for a more detailed answer.

How far away from the watercourse does my house need to be?

The location of the structure in proximity to a wash is dependent on the size of the wash and soil conditions.  The Floodplain Unit will review an application to determine if a location is acceptable during the building permit review.  In general, a minimum 20 foot setback is required from the top bank.  An Arizona Registered Civil Engineer may need to determine the appropriate setback or design appropriate erosion control measures.

Why do I need openings in my foundation (for floodplain development only)?

An important objective of the National Flood Insurance Program NFIP is to protect buildings constructed in floodplains from damage caused by flood forces.  Although the finished floor of a building may be well elevated above flood levels, if constructed on an enclosed extended foundation/stem wall with crawl space, these foundation walls are subject to flood forces which include hydrostatic pressure.  If the foundation/stem wall is not specifically designed to withstand hydrostatic pressure, they can cause damage to the structure.

In order to prevent such damages the NFIP has implemented the requirement for openings in foundation/stem and other enclosure (garage, detached non habitat structures) walls.  These openings allow automatic entry and exit of floodwaters.  During a flood event flood waters will reach equal levels on BOTH sides to the wall, thus reducing the potential; for damage from hydrostatic pressure.  Having proper flood openings may also reduce your cost of flood insurance.

Note: Depending on site conditions additional foundation requirements may apply. They are outlined in the following documents: 


Terms Of UsePrivacy StatementCopyright 2023 by Yavapai County Government
Back To Top