Do I need a floodplain use permit to build near a wash in Maricopa County?

You need a Floodplain Use Permit (FUP) if any part of your project falls inside a delineated floodplain, and building near a wash often puts you there. The Flood Control District of Maricopa County is direct in its Floodplain Regulations: "Where the watercourse is a delineated floodplain, no development shall take place in the floodplain without written authorization from the Board." That written authorization "is established herein as the Floodplain Use Permit signed by the Floodplain Administrator." A wash is a desert watercourse that carries runoff during storms. Many lots in North Scottsdale, Rio Verde, Cave Creek, and the unincorporated county sit next to one. If the wash and its floodplain are mapped, and your house, grading, or fill reaches into that mapped area, you need the permit before you build. The first step is a floodplain determination to find out whether your lot is affected at all. If it is, the FUP comes before construction, not after.

This page covers when the permit is required, how a wash triggers it, what the application takes, and the extra rules if your lot touches a floodway. It pairs with the drainage and flood-insurance pages for the full picture of building near water in Arizona.

When a floodplain use permit is required

A Floodplain Use Permit is required for development inside a delineated floodplain in unincorporated Maricopa County. The trigger is the floodplain, not the city limits. Section 401 of the county's Floodplain Regulations sets the scope plainly. "All development of land, construction of residential, commercial or industrial structures, or future development within delineated floodplain areas is subject to the terms of this regulation." It then states the core ban and its cure. "No development shall take place in the floodplain without written authorization from the Board," and that authorization is the FUP.

The word development is broad here. It is not just the house. It covers grading, fill, building, and other work that can change how water moves. So clearing a pad, importing fill, or placing a structure in the mapped floodplain all fall under the rule. The permit is how the Floodplain Administrator confirms your work will not block or divert flow in a way that threatens people or property.

There is a wrinkle for unmapped washes. If the watercourse near your lot has not been formally delineated yet, that does not let you skip the process. The regulation says if "the watercourse is not delineated, delineation may be required," and "once delineated, a Floodplain Use Permit shall be required prior to development." So an undelineated wash can still pull you into a delineation study first, then a permit.

How building near a wash triggers it

Building near a wash matters because the wash usually carries a mapped floodplain that can reach onto your lot. The closer your structure sits to the wash, the more likely it lands in that Special Flood Hazard Area (SFHA), the area shown on FEMA and county flood maps as having a 1-percent annual chance of flooding. The county notes that how close you can build to a wash "is dependent on the size of the wash, the amount of flow the wash carries, and if any bank stabilization is required." A small, low-flow wash may keep its floodplain narrow. A large wash can spread a wide floodplain well onto neighboring lots.

That is why you do not guess. You get a floodplain determination first. For property in the unincorporated areas of Maricopa County, you can call the Flood Control District's Floodplain Division at 602-506-2419 and ask whether your parcel is in a mapped floodplain. The answer tells you whether the FUP is in play before you spend money on design.

A few things commonly push a near-wash lot into permit territory:

• The floodplain edge crosses your building pad. If the SFHA reaches your house footprint, grading, or fill, the FUP applies.
• You need bank protection. Stabilizing the wash bank to protect the home is itself development in or near the floodplain.
• The wash is not yet delineated. An engineering delineation may be required before the county will issue the permit.

For how drainage review and floodplain review run alongside grading on a county lot, see what a drainage clearance is and the Maricopa County grading matrix.

What the floodplain use permit application takes

The application centers on showing where your structure sits, how high its floor will be, and that your work will not raise flood levels. On a residential build, the FUP is processed alongside the building permit through the county. The county lists the core pieces an application needs, including "an accurate plot/site plan and description of the property involved, description of proposed use, and finished floor elevations."

In practice, your engineer assembles a package built around a few items:

• Site plan and location map. A scaled plot plan showing the structure, the wash, and the floodplain, plus a location map tying the site to the nearest cross streets.
• Finished floor elevations. The elevation of the lowest floor, which has to meet the county's Regulatory Flood Elevation (RFE), the height the regulations require the floor to sit at or above. This is how a home near a wash stays dry in the design storm.
• Engineer's report. An engineering analysis of how the development affects flow, especially if any fill or structure is placed in the mapped area.
• Owner authorization. If a contractor or consultant signs for you, the county requires a notarized Property Owner Authorization Form.

The permit ties the design to the flood risk. The whole point is that the finished floor is high enough, and the work is shaped so it does not push floodwater onto someone else. Build the elevation and drainage in early, because raising a floor or reworking grading after design is set is expensive.

The extra rules if your lot touches a floodway

If your lot includes a floodway, the rules tighten, because the floodway is the high-velocity core of the watercourse. The floodway is the channel and the part of the floodplain that has to stay clear to carry the base flood without raising water levels. Maricopa County requires a special review there. Under the regulations, "any development in a floodway must be reviewed to determine if the development will increase flood heights," and "an engineering analysis must be conducted before a permit may be issued."

The standard that analysis has to meet is strict. The regulations allow development only where "no increase in the Base Flood Elevation would result and that no increase in flood levels within any designated floodway during the base flood discharge would result." That is the no-rise rule. Your engineer has to certify that your house, fill, or bank work does not raise the flood at all anywhere in the floodway. This is the hardest part of building close to a wash. It sometimes means pulling the structure back out of the floodway entirely.

A floodplain that is not a floodway is more forgiving but still regulated. The county allows a limited rise in the base flood, generally up to one foot, under controlled encroachment rules. Either way, the elevation and no-rise requirements are why an early floodplain determination saves money. For why a lender will likely require flood coverage on top of all this, see whether you need flood insurance on a construction loan in Arizona.

County floodplain maps, fees, and elevation standards change as washes are restudied and the regulations are updated. So confirm your parcel's current floodplain status, the active FUP requirements, and current fees (as of 2026) with the Flood Control District of Maricopa County before you design. A builder who works near desert washes, like Jematell Homes, runs the floodplain determination early. We set the finished floor and the drainage to the county standard, then pull the Floodplain Use Permit before the grader arrives, so a wash next door does not stall the build or flood the home.

The Jematell Homes approach

We handle jurisdiction, submittals, and inspections as part of every build. We would rather answer your questions before you build than after, so get in touch any time.

Sources

• Flood Control District of Maricopa County: Floodplain Regulations (Section 401, Floodplain Use Permit Required; floodway encroachment certification)
• Maricopa County: Floodplain Use Permits (application requirements; floodplain determination)
• Maricopa County Planning & Development: Drainage and floodplain FAQs (proximity to a wash; floodplain determination 602-506-2419)