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Valley Water sensor recalibration leads to erroneous flood alert

Aug 08, 2023


Valley Water sensor leads to erroneous automated flood alert for Los Gatos Creek. A similar notice was issued in the North Bay.

LOS GATOS, Calif. - The weather conditions and a technology-driven, automatic alert didn’t add up. Under sunny skies in the Bay Area, Wednesday, an automated system posted a notice from the National Weather Service saying a portion of the 24-mile-long Los Gatos Creek had reached thousands of feet high.

"So why would they do that? I guess that’s the question…why would they put something out that…I mean, if they’re gonna put an announcement out like that, maybe they should have some justification or reinforcement of the information on that," said Robert Lira, who was walking along the creek-side trail during his lunch break.

But there wasn't actually a human behind the alert.The overnight notice went to the NWS website and automatically showed water levels on Los Gatos Creek going from 1 foot to 1,800 feet, equivalent to ocean level depth.

A similar alert was also issued for Santa Rosa Creek, where levels reached, supposedly, 7,700 feet. In both cases, the information was wrong.The NWS later told KTVU it was aware that Valley Water was calibrating its equipment at the time and therefore discounted the reading from a sensor managed by the agency.

According to a NWS spokesman, the system in question, "…transmits data from sensors at the Valley Water site to a satellite, and then it’s transferred into a government server in Maryland."

"A carryover glitch occurred, causing a multiplier effect," which caused the numbers to be exaggerated.

Staffers didn’t notice the problem until a pop-up alert on their computers signaled water levels were registering above flood stage.

"The National Weather Service saw it. They’re used to this. They say it’s not uncommon for faulty sensors or things like that, all across California. So they gave us a call just to let us know obviously…some missing data points. They looked at the data, and it was clearly inaccurate," said Matt Keller, a spokesman for Valley Water.

He said the problem occurred as his agency was recalibrating flood sensors along Los Gatos Creek, near Lark Avenue, in Los Gatos. Water level reporting times are typically adjusted when it’s not raining, to better predict trouble during the rainy season, when residents are in danger of flood conditions.

"I guess that it is a good thing that they’re doing that. So that it works better," said Lisa Lane, who was walking along the Los Gatos Creek Trail Wednesday.

Added Keller, "During the last winter, how important it was that we were updating all the information. We worked with all the cities here in Santa Clara County to make sure they had updated information on what the rivers and creeks were doing."

In this case, sensors in the South and North Bays signaled an alarming increase in water height.

"The National Weather Service deals with these during the summer. They say this is the best time to do it. It’s not during the wet season," said Keller.

He said the alert was only posted to the NWS website and did not go out as a "flood warning" to individual neighborhoods or area first responders. A "warning" is a serious alarm to the surrounding community about dangers to life and property.

This notice was not that.

Officials with the NWS said their goal is to get information out as quickly as possible in times of an actual crisis, and they monitor erroneous reading like this one.

CORRECTION: This story previously referred to the erroneous flood alert as a "warning," which is a call to action regarding public safety from the NSW. It has since been corrected.

Jesse Gary is a reporter based in the station's South Bay bureau. Follow him on Twitter, @JesseKTVU and on Instagram, @jessegontv

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By PublishedUpdatedLOS GATOS, Calif.CORRECTION: This story previously referred to the erroneous flood alert as a "warning," which is a call to action regarding public safety from the NSW. It has since been corrected.