Map Layers & Data

🌊 FEMA Flood Zones: Official maps showing federal flood risk areas. Use these to understand your long-term risk and insurance requirements.

🧵 USGS Stream Network: A detailed map of rivers, creeks, and waterways from the NHD (National Hydrography Dataset). Color-coded by stream type — darker blue lines indicate perennial waterways.

📡 NEXRAD Radar: High-resolution live precipitation data from NOAA/NWS. Essential for tracking active storms and seeing where heavy rain is currently falling.

📍 USGS River Gauges: Real-time sensors measuring water depth. These provide immediate warnings when local rivers reach critical flood stages.

🦆 Wetlands: Transition zones where water covers the soil. These areas provide natural flood storage and are sourced from the USFWS (U.S. Fish & Wildlife Service).

🔗 View Open Source Licenses & Data Credits →

Technical Terms & Abbreviations

• SFHA (Special Flood Hazard Area): The land area covered by the floodwaters of the base flood. In these areas, the NFIP's floodplain management regulations must be enforced and the purchase of flood insurance is mandatory.

• BFE (Base Flood Elevation): The elevation to which floodwater is anticipated to rise during the base flood (100-year flood).

• Elevation Level (Ground): The estimated height of the ground surface at a specific point relative to sea level, sourced from the USGS 3D Elevation Program.

• Storm Surge Level: The rise in seawater level caused solely by a storm, over and above the normal predicted tide.

USGS Stream Network Colors

Blue: Perennial streams & rivers — flow year-round.

Dashed Blue: Intermittent streams — flow seasonally.

Cyan: Canals & ditches — human-made water channels.

Magenta: Pipelines — water moving through pipes or conduits.

Yellow: Aqueducts — large scale artificial water transport.

Red: Coastline — the boundary line between land and sea.

Filled Blue Area: Lakes, reservoirs, and ponds.

FEMA Zone Legend

• Zone A: High Risk. 1% annual chance of flooding. No Base Flood Elevations (BFEs) determined.

• Zone AE: High Risk. 1% annual chance of flooding. BFEs have been determined.

• Zone AH: High Risk. 1% annual chance of shallow flooding (usually ponding), with depths between 1 and 3 feet. BFEs determined.

• Zone AO: High Risk. 1% annual chance of shallow flooding (usually sheet flow on sloping terrain), with depths between 1 and 3 feet.

• Zone AR: High Risk. Temporarily increased risk due to the building or restoration of a flood control system (levee/dam).

• Zone A99: High Risk. Areas to be protected by a federal flood control system where construction has reached statutory milestones.

• Zone V / VE: Coastal High Hazard. High risk areas subject to storm-induced velocity wave action. (VE has BFEs determined).

• Zone X (Shaded): Moderate Risk. 0.2% annual chance of flooding (500-year flood).

• Zone X (Unshaded): Minimal Risk. Areas outside the 0.2% annual chance floodplain.

• Zone D: Undetermined Risk. Areas where flood hazards are undetermined, but flooding is possible.

• Regulatory Floodway: The channel of a river that must be kept clear to discharge the base flood without increasing water levels.

• Reduced Risk Due to Levee: Areas protected by levees from the 1% annual chance flood. Levees do not eliminate all risk.

USGS River Gauge Stages

🟢 Normal: Water levels are within the typical, expected range.

🟡 Action: The river is nearing its banks. Start preparing and monitor closely.

🟠 Minor: Nuisance flooding begins. Low roads, yards, and parks may be covered.

🔴 Moderate: Significant flooding. Some buildings may be impacted and local roads closed.

🟣 Major: Severe, life-threatening flooding. Extensive damage and evacuations are likely.

Data Sources

FEMA: Federal Emergency Management Agency (Flood Zones)

USGS: United States Geological Survey (Streams, Elevation, Gauges)

NOAA/NWS: National Weather Service (Precipitation Radar & Alerts)

USFWS: U.S. Fish & Wildlife Service (Wetlands Data)

ArcGIS: Map infrastructure & geocoding services.

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