Marin City, California
Torrential rains. High tides. The water cannot get out.
Marin City sits in a bowl: roughly 344 acres of hillside and flat drain to the low ground around Drake Avenue and Donahue Street. The water has only one way to leave: a (a concrete box) under the Highway 101 embankment, with a on it (the county's photograph of the gate). Water can leave that way only when Richardson Bay is lower than the floor of that box. Right now:
Asking NOAA what the bay is doing…
3D model
Marin City in 3D
The bowl, the culvert and the bay from the air. Turn it, zoom in, or raise the water to see where it would reach.
Slide, type a depth or pick one to raise the water by hand and see what it looks like.
Drag to turn · Ctrl + scroll to zoom · shift-drag to slide · arrows and W A S DDrag sideways to turn · two fingers to slide or pinch to zoom
About this drawing
The ground is the lidar's and the streets are OpenStreetMap's, drawn at the widths the lidar measures between their curbs. On the town side of the freeway the buildings are stand-ins, not survey, at the sizes and heights Marin City's run to, and nothing there depicts a specific property, with three exceptions. The Marin Gateway's buildings, parking lot, walks and trees come from OpenStreetMap and the lidar; its big store is labeled Target at residents' request. Golden Gate Village's buildings are their real footprints from OpenStreetMap, at the roof heights the lidar measures. And the floating homes across the bay: every dock and home is where OpenStreetMap's survey puts it, at the size it gives it, and they rise and fall with the bay — only their heights and colors are made up. On the bay side of the freeway the buildings are the map's real ones, as they are past the tile.
Highway 101 crosses on its embankment, not a bridge: the pond's water goes under it through a box culvert, drawn in coral straight through the bank at its true size — six feet by 38 inches, a thread from this distance. The cross-section above looks along the dashed line, the streets on your left and the bay on your right.
The lidar tile the model runs on is about half a mile by two-thirds. For about a mile and a half beyond it the ground is the same lidar averaged to 15 m near the town and 40 m farther out — coarser, drawn a touch paler, and faded at the far edge so the map does not end at a cliff. Those rings put the ridge above Golden Gate Village and the hills toward Sausalito and Tam Junction in the picture; the flood model never reads them.
The parks, playing fields, playgrounds and golf, the trails and fire roads, and the scrub, woods and beaches on the hills are painted on the ground where OpenStreetMap maps them. The play structures on the playgrounds are generic, and a field gets only a boundary and a halfway line, since the data the model reads does not say what sport it is for.
The roads on those rings are OpenStreetMap's for about the first third of a mile and the federal road layer's beyond, and they go where they really go, including Highway 101 curving north onto the first spans of the Richardson Bay Bridge. Past the tile the freeway is cut into the hillside at its own grade, since a 15 m average of a steep slope is the slope, not the road. The traffic is a picture, not a count; its signals and signs are placed by the kind of road that meets there, not copied from the real intersections. Beyond the tile the flood simulation's water shows only once it is higher than Highway 101 at its low point, when the bowl and the bay are drawn as one water.
Water on your street?
Stay safe
- Stay out of it if you can. Moving water is dangerous well before it reaches your knees.
- Do not drive through it. Even a shallow sheet of water can make a car hydroplane: water gets between the tires and the road, they stop gripping, and the car slides with no real steering or braking.
- Deeper water is worse. About a foot of moving water can carry a car off, and you cannot see the road under it.
Then, from dry ground
- Take a photo with something of known height in it: a curb, a car tire, a door.
- Note when you took it. Then:
Reading the forecast…
Where to go
Everything on this site is behind one of these five doors
Why it happens
The bowl, the one culvert, and the gate that shuts when the tide is high. Plus the three things that would change it.
What is being done
Who is doing what about it, with what money and on what dates. And what residents have asked for.
What you can do
Measure a flood photo, post what is happening on your street, and find out who is responsible for what.
Check the work
Where every number came from, what the documents actually say, and the studies themselves.
Becoming a town
What Marin City could decide for itself as a town, and what it would take to become one.