Where It Flows shows, in 3D, where rain water runs and gathers around real houses and streets. It is free, has no accounts, no tracking and no ads that follow you. The source code is open.
Do not use it to decide insurance, building, or evacuation. Storm drains, curbs, walls and fences are only partly known. Ask your city or county flood office for official guidance.
| Layer | Source | License |
|---|---|---|
| Terrain | USGS 3D Elevation Program lidar | Public domain |
| Buildings, streets | OpenStreetMap contributors | ODbL, attribution |
| Flood zones | FEMA National Flood Hazard Layer | Public domain |
| Rain amounts | NOAA Atlas 14 | Public domain |
| Official flood model and storm drains (this demo) | Flood Control District of Maricopa County, Upper East Fork Cave Creek study | Public data, see their terms |
Two models are shown. The official one is the county flood district's FLO-2D study, which includes storm drains and ground soak-in. The other is a simple terrain-only model: houses are solid blocks, rain arrives in one burst, 80 percent runs off. It is pessimistic and shows where water goes and gathers, not how long it stays. In the demo it flags far more deep water than the official model, so the official model is the default.
MIT license. Repository link goes here once published.
Only this demo neighborhood so far. Any address in the United States comes next; places without lidar or drain records will be labeled with lower confidence.