Floodplain
A floodplain is the land adjoining a river, stream, watercourse or lake that is likely to be covered by floodwaters. Federal flood rules map the part of it with a one percent or greater chance of flooding in any given year as the special flood hazard area.
Virginia's flood plain and FEMA's special flood hazard area describe the same ground in different terms
Virginia's flood protection statute defines a flood plain as the areas adjoining a river, stream, watercourse, ocean, bay or lake that are likely to be covered by floodwaters. The federal flood insurance rules put a number on it: the area of special flood hazard is land in the flood plain with a 1 percent or greater chance of flooding in any given year.
The state's words describe the ground. The federal words describe a probability drawn on a map, and that map is what a lender, a permit office and an insurer actually read. Most of the terms a buyer meets on a flood question come from that federal side.
- Flood plain (Va. Code 10.1-600)
- The areas adjoining a river, stream, watercourse, ocean, bay or lake likely to be covered by floodwaters.
- Hundred year flood (Va. Code 10.1-600)
- A flood level with, on the average, a one percent chance of being equaled or exceeded in any given year at designated locations.
- Special flood hazard area (44 CFR 59.1)
- The same thing as the area of special flood hazard: land in the flood plain subject to a 1 percent or greater chance of flooding in any given year.
- Base flood (44 CFR 59.1)
- The flood having a one percent chance of being equaled or exceeded in any given year.
- Regulatory floodway (44 CFR 59.1)
- The channel and the adjacent land that must be kept open to carry the base flood without raising the water surface more than a designated height.
The hundred year flood and the base flood are the same idea stated twice, once in state law and once in federal rule. The floodway is a narrower idea again: the channel and the land beside it that are held open for the base flood itself. Whether and how a house goes up on mapped ground belongs to can I build in a floodplain.
None of these terms is a landform. Low, level ground beside a stream has a name of its own, bottomland, and a bottom may or may not sit inside the mapped area. The same goes for a big river: whether a stretch of New River frontage floods is a map and history question, not something the word floodplain settles.
On a Floyd County plat and a Carroll County permit form, the word turns into a map reference
In a land sale in this part of Virginia, floodplain rarely arrives as a definition. It arrives as a shaded patch on a plat or a row of blanks on a permit form.
Floyd County's land development ordinance requires a plat to state the FEMA flood zone the property lies in and the Flood Insurance Rate Map it comes from, and to identify all land in the 100-year floodplain by cross hatch or shading. On a plat drawn to that ordinance, a buyer can see the flood ground marked. The rule is Floyd County's own and stops at the county line; Meadows of Dan, for one, is in Patrick County, where the Floyd ordinance does not reach.
Carroll County's floodplain development permit application covers development in a Special Flood Hazard Area on the effective FEMA map, and two of the federal terms above, the floodway and the base flood elevation, turn up as blanks on it among the map lines it asks for. Galax, the independent city beside Carroll and Grayson in the Twin Counties, handles floodplain permits through its own Building Official.
Both documents point back to one federal source, FEMA's Flood Map Service Center, and how to read the panel a search there returns, zone by zone, is walked through in reading a floodplain map.
Does your plat show a shaded flood zone?
Send the county and the plat or tax map number, and Lowell will read the flood zone against the ground and tell you which office confirms it. No cost, no obligation.
Got it. Thank you.
We'll be in touch shortly with an honest read.
Questions about this term
Does a hundred year flood mean the water comes up once a century?
No. Virginia's statute defines the hundred year flood as a flood level with, on the average, a one percent chance of being equaled or exceeded in any given year at designated locations. The chance applies every year, so a flood of that level in one year does not make one the next year less likely, and the name describes a probability rather than a schedule.
Is the regulatory floodway the same as the special flood hazard area?
No. The special flood hazard area is all the land in the flood plain with a one percent or greater annual chance of flooding. The regulatory floodway is defined more narrowly: the channel and adjacent land that must be reserved to carry the base flood without raising the water surface more than a designated height. Carroll County's permit application asks about each one separately.
Where this page's facts come from
Every rule, office and figure above traces to one of these. Rules change; check the office before you act on one.
- Va. Code 10.1-600: flood protection definitions Code of Virginia
- 44 CFR 59.1: NFIP definitions Code of Federal Regulations
- Flood Map Service Center FEMA
- Floodplain development permit application (PDF) Carroll County
- Land development ordinance (PDF) Floyd County
- Building Official City of Galax