{"id":8709153,"date":"2023-01-08T05:55:30","date_gmt":"2023-01-08T13:55:30","guid":{"rendered":"https:\/\/www.eastbaytimes.com\/?p=8709153&preview=true&preview_id=8709153"},"modified":"2023-01-09T05:07:31","modified_gmt":"2023-01-09T13:07:31","slug":"how-early-warning-systems-help-us-predict-flooding","status":"publish","type":"post","link":"https:\/\/www.eastbaytimes.com\/2023\/01\/08\/how-early-warning-systems-help-us-predict-flooding\/","title":{"rendered":"How early warning systems help us predict flooding"},"content":{"rendered":"

A stream gauge is a humble thing.<\/p>\n

But the Bay Area\u2019s 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.<\/p>\n

\u201cWe can tell first responders, with some certainty, that our gauges are saying it\u2019s going to be a flood-prone area in one hour and 45 minutes,\u201d said Kevin Murray of the Palo Alto-based San Francisquito Creek Joint Powers Authority. \u201cThat gives them some time to get ahead of the disaster.\u201d<\/p>\n

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. After last Saturday\u2019s fierce storm, they ask: Is the equipment still working? Have flow conditions changed due to downed trees, clogged bridges, eroded banks or blocked storm drains?<\/p>\n

\"Katie
Katie Leonard, of Pleasant Hill, left, assists Scott Mathers, of Pleasant Hill, as they rescue Mathers\u2019 mother Patsy Costello, 88, of Pleasant Hill, after being trapped in her vehicle for over an hour on Astrid Drive in Pleasant Hill, Calif., on Saturday, Dec. 31, 2022. Costello drove her car on the flooded street thinking she could make it when it stalled in the two feet of water. After two hours the water had receded about a foot making it easier to rescue her. Police were called but stood by and watched after calling in a tow truck to help pull the car out of the water. Nurse Katie Leonard, of Pleasant Hill, lives down the block used her kayak to bring Costello hot tea, blankets, food and a phone to call a friend. (Jose Carlos Fajardo\/Bay Area News Group) <\/figcaption><\/figure>\n

\u201cWe\u2019ve been out with replacement equipment, assessing problems, assembling the pieces and doing repairs so that everything is operational,\u201d said geologist Scott Brown with Berkeley-based Balance Hydrologics, a consulting firm that helps Bay Area agencies manage flood warning systems.<\/p>\n

\u201cWith additional storms coming, we need to mobilize fast in order to get everything back up and running again,\u201d he said.<\/p>\n

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 warnings, is growing.<\/p>\n

The gauges can provide days or hours of advance notice, giving residents time to sandbag, move cars, help the homeless, lift electronics and precious antiques off the floor \u2014 or seek higher ground.<\/p>\n

On New Year\u2019s Eve, a gauge on the Stanford campus alerted authorities at 8:43 a.m. that San Francisquito Creek, between Santa Clara and San Mateo counties, had reached \u201cflood monitoring stage\u201d and was continuing to rise. At 9:06 a.m., officials issued a public flood advisory. At 9:30 a.m., residents were alerted that within a half-hour, flooding was likely at Palo Alto\u2019s narrow Pope-Chaucer Bridge. Water rose to about 21 feet, frighteningly close to overflowing the creek banks.<\/p>\n

\"A
A 2016 file photo of the Windy Hill Preserve rain gauge in the Santa Cruz Mountains near Los Altos Hills. The rain gauge is part of a network of gauges, sensors and computers that are helping save lives and property in vulnerable to flooding in Bay Area communities. (Patrick Tehan\/Bay Area News Group) <\/figcaption><\/figure>\n

Other watersheds may allow more time, and earlier warning, said Jack Xu, senior engineer at Santa Clara Valley Water District. For instance, flooding along San Jose\u2019s Guadalupe River can be forecast two to three hours in advance. Coyote Creek flooding may take a day. But in urban concrete channels, water may need only 30 minutes to flow from the mountains to downtowns.<\/p>\n

Surveillance starts two to three weeks in advance of a storm, said Xu.<\/p>\n

Weather is notoriously tough to predict in the Bay Area, a mountainous landscape perched on the edge of the cold ocean. Low and fast-moving jets of moist air scatter into a patchwork quilt pattern of precipitation, affecting locales differently.<\/p>\n

Looking ahead at long-range weather forecasts, Xu said, \u201cWe see: \u2018Is it a wet pattern? Is it a dry pattern?\u2019 When you see back-to-back storms, you know you have to plan resources and think, operationally, about how you\u2019re going to move water, if you need to.\u201d<\/p>\n

Plans get more targeted as time draws near, because forecasts improve within 10 days of a storm. \u201cBut if the forecast is inaccurate, everything downstream is wrong,\u201d said Xu.<\/p>\n

Using computer models, they calculate how much of the predicted rainfall will become runoff, based on past history, soil saturation and local geology.<\/p>\n

The big decisions start five days before a storm, Xu said. There are regional conference calls with PG&E, other utilities and various cities, where they ponder: Should they release water from reservoirs to make room for additional runoff? Do they need to boost staffing? \u201cWe weigh the consequences with the risk,\u201d Xu said.<\/p>\n

Crews on the ground assess a creek\u2019s condition, looking for debris and other risks. This effort is intensified\u00a0if winds are forecast.<\/p>\n

Once the storm lands, the role of rain gauges becomes critical. Perched in distant mountains, these gauges \u2014 pipes with a funnel, bucket and tipping mechanism at the top \u2014 measure precipitation. They tell officials what to expect.<\/p>\n

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.<\/p>\n

Contra Costa County Flood Control & Water Conservation District manages 32 rain gauges and 16 stream gauges. The Santa Clara Valley Water District has a network of 70 stream and rain gauges. Alameda County has about 90 rain and stream gauges.<\/p>\n

These gauges, powered by solar panels, send electronic signals to data loggers via radio, landlines, cell phone signals or satellites. With ever-increasing computer power, software processes the many signals into a computer database, which monitors the information as it is received. It triggers a warning when certain thresholds \u2014 say, water filling 80 percent of a creek\u2019s capacity \u2014 are reached.<\/p>\n

A new Contra Costa County-based radar system will enhance the detail and accuracy of weather forecasts, helping local flood protection efforts. Installed on Dec. 7, 2022, a humming \u201cX-band\u201d radar unit on Rocky Ridge in San Ramon is designed to detect discrete patches of incoming moisture. It is part of a five-radar project funded through Proposition 84. (Photo courtesy of Mark Boucher, Contra Costa County Flood Control and Water Conservation District) <\/figcaption><\/figure>\n

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.<\/p>\n

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\u2019s easier to transmit real-time information, Xu said. Supercomputing allows more advanced calculations, under many different scenarios.<\/p>\n

New \u201cX-Band Radar\u201d 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 \u2014 including Marin, Sonoma, San Francisco and Santa Cruz \u2014 that will provide local data about atmospheric rivers.<\/p>\n