Surface Water Data Portal
Demo snapshot · July 28, 2026 at 4:53 PM PT · not current conditions
About
Every number on this site is one of four things. Knowing which one you are looking at is most of what it takes to read a creek.
How high the water surface sits, measured against a fixed reference at that specific gauge. Stage is local. Six feet at one bridge and six feet at the next bridge are not the same amount of water and were never meant to be compared. This is why every threshold on this site belongs to one gauge and travels nowhere.
How much water is moving past the gauge. A cubic foot is about seven and a half gallons, so Coyote Creek at 8,550 cubic feet per second was moving roughly 64,000 gallons past Gilroy every second. Discharge is comparable between places in a way stage is not.
How much a reservoir is holding. An acre-foot covers an acre a foot deep, about 326,000 gallons. Storage matters downstream because what a reservoir cannot hold, it passes on.
Accumulated depth at a rain gauge over one hour, six, twenty-four, or since the water year began in October. Rain is the leading indicator: it lands on the ridge before it shows up in the creek.
A threshold is a stage that Valley Water has decided means something at that exact location, numbered from the first sign of trouble upward. They are not statistical, they are not a forecast, and they are not the same from creek to creek. They are an operational judgment about a specific channel, written down by the people who maintain it.
What makes them unusually useful here is that Valley Water publishes prose with them. For 33 of its gauges the district says, in its own words, what goes under water at each numbered level, naming streets, schools, parks and neighborhoods. That prose is the most specific flood information a resident of this county can get, and until now it has been buried a click deep behind a map pin.
The place index is built from nothing but those descriptions
Three separate systems watch water in this county, and they do not agree about which stations exist.
| Network | In this build | What it is for |
|---|---|---|
| Valley Water sensors | 119 stream, 48 rain, 10 reservoir | The district's own operational network, telemetered continuously. 44 stream gauges are in the flood watch set and 22 carry a forecast model. |
| USGS stream gauges | 10 cross referenced | Federal gauges with a long instantaneous record. Valley Water publishes the USGS number for the ones it also carries, which is what lets the storm replays link back to a live gauge page. |
| NOAA forecast points | 145 in the county | National Weather Service gauges with flood categories and a written impact library. Not all of them cross reference to a USGS station, and some of the most important ones do not. |
34 of the district's sensors are flagged as SB 88 diversion monitoring rather than flood warning, and they are labelled that way on their own pages. A gauge that is not reporting is shown as not reporting. It is never drawn at zero, because an instrument that is down and a creek that is dry look identical on a chart and are completely different facts.
Readings arrive automatically and are published before anyone has reviewed them. Sensors drift, intakes silt up, debris piles against a stilling well, and a rating curve that converts stage to discharge is a model that gets revised. The federal archive marks records provisional until they are checked, and this site keeps that marking rather than quietly presenting everything as final.
In practice: trust the shape more than the last digit, and trust a rise more than an absolute number. If a reading looks impossible, it might be.
Call 911. This site reports what sensors measured; it does not know where you are, it cannot see your street, and it does not issue evacuation orders. Those come from your city and the county.
Valley Water is at 5750 Almaden Expressway in San Jose, and the district's general line is (408) 265-2600.
Readings on this working copy were captured July 28, 2026 at 4:53 PM PT.