A stream gauge is a humble thing. But the Bay Area’s vast network of gauges, strategically placed and linked to powerful telecommunication lines and computers, offer early warning of rising waters, helping protect lives and property from flood damage.
“We can tell first responders, with some certainty, that our gauges are saying it’s going to be a flood-prone area in one hour and 45 minutes,” said Kevin Murray of the Palo Alto-based San Francisquito Creek Joint Powers Authority. “That gives them some time to get ahead of the disaster.”
This week, with a series of storms just past and more on their way, experts patrolled rivers and creeks to inspect and recalibrate their precious tools to ensure the accuracy of water data.
“We’ve been out with replacement equipment, assessing problems, assembling the pieces and doing repairs so that everything is operational,” said geologist Scott Brown with Berkeley-based Balance Hydrologics, a consulting firm that helps Bay Area agencies manage flood warning systems. “With additional storms coming, we need to mobilize fast in order to get everything back up and running again.”
Even as climate change increases the risk of floods, protection strategies are shifting away from structural measures, such as walls, gates and levees. The role of prediction — and technology — is growing.
The gauges can provide days or hours of advance notice, giving residents time to position sandbags, move cars, help the homeless, lift electronics and precious antiques off the floor — or seek higher ground.
Using computer models, they calculate how much of the predicted rainfall will become runoff, based on past history, soil saturation and local geology.
Once the storm lands, the role of rain gauges becomes critical. Perched in distant mountains, these gauges — pipes with a funnel, bucket and tipping mechanism at the top — measure precipitation. They tell officials what to expect. Stream gauges have a membrane that precisely measures the depth of water and converts it into a flow rate.
They transmit every hour and send a packet of four 15-minute time stamps. When a certain threshold is reached, the sensors can send data every five minutes. These gauges, powered by solar panels, send electronic signals to data loggers via radio, landlines, cellphone signals or satellites. With ever-increasing computer power, software processes the many signals into a database, which monitors the information as it is received. It triggers a warning when certain thresholds — say, water filling 80 percent of a creek’s capacity — are reached.
When waters run high, officials must decide whether to issue an electronic flood alert to local residents downstream. Because different locations have different flood risks, the warnings can be localized.
A revolution in technology is allowing for better forecasting. Over the past decade, the National Weather Service has developed weather models that are better suited to the West Coast, and widespread availability of cell services means it’s easier to transmit real-time information, said Jack Xu, senior engineer for the Santa Clara Valley Water District. Supercomputing allows more advanced calculations, under many different scenarios.
New “X-Band Radar” is helping estimate rainfall in specific communities. In Contra Costa County, radar was installed last month on Rocky Ridge near Las Trampas Regional Preserve, according to hydrologist Mark Boucher. Radar for the Santa Clara Valley Water District sits atop the Penitencia Water Treatment Plant facility. They are part of a future regional network of radars — including Marin, Sonoma, San Francisco and Santa Cruz — that will provide local data about atmospheric rivers.
Such tools are increasingly important because human-caused climate change will lead to more powerful storms unleashing substantially more water in the Bay Area, according to a joint research collaboration between the city of San Francisco and Berkeley Lab.
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