Where Birmingham floods — vs. where FEMA says it floods.
Toggle the layers on the map below to compare our calibrated 100-year flood model against FEMA's regulatory flood map. Most of the flooding sits outside what the FEMA map shows.
Layers
Depth opacity
85%
Floodway (no-build)
100-yr SFHA
500-yr (0.2%)
Depth scale
anklekneewaistchestover head
0.5–1 ft (ankle/knee) impassable to cars · 2 ft (waist) damages first-floor structures · 6+ ft (over head) life-safety
Where it floods
How much area floods in a 100-year storm under our model, compared to the FEMA flood map. Numbers in square miles.
| Watershed | Our model (mi²) | FEMA map (mi²) | Difference (mi²) | % off FEMA's map |
|---|---|---|---|---|
| Valley Creek | 28.1 | 5.1 | 23.0 | 86% |
| Village Creek | 40.7 | 6.4 | 34.3 | 90% |
| Fivemile Creek | 46.0 | 3.0 | 43.0 | 94% |
| All three watersheds | 114.8 | 14.5 | 100.3 | 87% |
Buildings affected
How many buildings sit in flood water during a 100-year storm, and how many of those are on FEMA's flood map.
| Watershed | Buildings flooded | On FEMA's map | Off FEMA's map | % off the map |
|---|---|---|---|---|
| Valley Creek | 7,876 | 643 | 7,233 | 92% |
| Village Creek | 5,745 | 464 | 5,281 | 92% |
| Fivemile Creek | 2,354 | 103 | 2,251 | 96% |
| All three watersheds | 15,977 | 1,210 | 14,767 | 92% |
How the model was built
Short version of the engineering, for staff who want to know it's defensible.
- Coverage. 186 sq mi covering the three watersheds that drain through Birmingham — Valley, Village, and Fivemile Creek.
- Method. A 2D rain-on-mesh hydraulic model (HEC-RAS 7.0). Rain falls on every cell, then water flows downhill across the surface. Captures the street-and-yard flooding that FEMA's older 1D channel-only models miss.
- Calibrated. Tuned against ten USGS streamgages inside the model area.
- Demo only — not a final deliverable. This is a working demonstration. The model does not capture the City's underground storm-sewer network; representing it accurately requires field survey of pipe inverts, sizes, and conditions across the system. That work is part of the master-plan scope.
Contact
Jacob Beatty, P.E. · jbeatty@dccm.com