A new weather radar planned for the top of Mount Barnabe will add detail to meteorologists’ predictions for atmospheric rivers and Marin County’s ability to predict and prepare for flooding. The Bay Area’s capacity to foresee and respond to atmospheric rivers is currently handicapped by a lack of precise radar coverage in Marin and the Pacific Ocean, where the low-lying storms form.
In communities where king tides and shallow water tables compound the effects of heavy rainfall, the roughly 60-mile-radius radar could save millions in infrastructure and human lives, said Roger Leventhal, a hydrologist for the Marin County Flood Control District.
“When it rains, it doesn’t do so uniformly, but rather in cells,” Mr. Leventhal said. “Knowing the location and intensity of these cells is especially important here.”
The installation of the C-band radar is part of a regional advanced-quantitative precipitation information project that uses radars, watershed measurements and flood patterns to track atmospheric rivers. Sonoma Water is helming the project, a partnership between local, state and federal agencies and academic research centers like the Cooperative Institute for Research in the Atmosphere at Colorado State University. The project is receiving roughly $30 million in grants from the California Department of Water Resources, the California Office of Emergency Services, FEMA and other agencies. The Mount Barnabe radar will cost around $2 million.
Currently, five smaller X-band radars track local storms in Sonoma, Santa Cruz, Contra Costa, Santa Clara and San Mateo Counties. All have a range of about 25 miles, and they leave pockets uncovered. Marin is almost completely excluded from their coverage.
Another system that uses S-band radars to track precipitation was installed in the ’90s and is usually pointed too high to gather accurate data on low-lying atmospheric rivers. The only S-band radar in the Bay Area is on Mount Umunhum in Santa Clara.
Atmospheric rivers produce up to half of the annual precipitation on the West Coast. Though their frequency will likely diminish as climate change worsens and more water goes into the atmosphere, the storms will grow wider, longer and more intense.
Marin, with over $2 billion in damages over the last 40 years, has seen the fourth highest proportion of losses caused by atmospheric rivers in the country, behind Sonoma County, Los Angeles County and Lewis County, Wash. With the new radar system, Marin’s flood control managers could take data from the forecast models and cross reference it with areas sensitive to flooding.
The radar, which will be built on property owned by the county, is meant to operate only when it is raining or about to rain. It will not be used to track temperature patterns or wildfire.
Mount Barnabe was deemed an ideal location since the site is already developed with power and internet towers. Mount Tam’s East and West peaks were both considered but the land is currently leased to a private company and a federal aviation radar on West peak would interfere with reception.
Last week, the project’s leads presented the plans to valley residents in a Zoom meeting. Attendees expressed frustration with what they described as unchecked county development in an area where standards are strict for residents. They also worried about potential adverse health effects from radiation and possible damages to the private roads—Arroyo Road, Alamo Way and Portola Road—that construction crews will have to use.
When a Verizon cell tower was installed on Mount Barnabe in 2008, the increase in traffic made it difficult to identify which construction teams were responsible for damages, local Kenneth Hillan said. After the tower was installed, residents thought they were seeing the last development on the mountain.
Dale Roberts, the project manager and a principal engineer at Sonoma Water, said crews would film the road before work begins. “After the end of the project, we go through and if there’s damage, we have them repair those sections,” he said.
One of the chief concerns from residents was the character of the skyline, but because the radar is a government project on government land, it is exempt from the discretionary permitting process, including for ridgeline permits. Mr. Leventhal said the plan is to make the 20-foot-tall structure beige so it blends into the background. It will have no external lights.
Mr. Hillan and other residents expressed the need for a development roadmap. “It’s sort of like the government just has the right to do what they want with these things,” local Peggy Duggan said.
Jean Berensmeier, who founded and sits on the San Geronimo Valley Planning Group, said the group only recently found out about the project. “We deserve to be contacted on this project and make a recommendation, especially because there are environmental and health concerns,” she said. “We’ve been around since 1972 and we’ve met with the county many times over the years, but this is unacceptable and rude.”
Residents were also worried about cumulative radiation from the internet, and Marin Emergency Radio Authority towers and C-band radar. According to Chandraselaran Venkatachalam, the technical advisor to the project and professor at Colorado State University, the average power from a C-band radar is 250 watts, roughly 500 watts less than the average microwave and below the Federal Communications Commission recommended levels for the general population.
The radar is set to be installed between a Cal Fire lookout tower and the Verizon tower, positioned 10 feet above ground on top of a shipping container placed on a 24-by-16-foot concrete pad. A spherical enclosure will protect the antenna from the elements and focus the energy in one direction much like a lighthouse, scanning vertically and horizontally to create an image of the atmosphere.
The construction will involve a five-ton crane, a concrete mixer, various work trucks and other heavy equipment. The county will lease the land to Sonoma Water once they get approval from their respective boards to execute the agreement. In Marin, the Department of Public Works will present the lease to the Board of Supervisors on March 7. On April 4, the Sonoma Water board of directors will consider authorizing the execution of the lease. Sonoma Water and the Marin County Department of Public Works are preparing California Environmental Quality Act exemption documents and Sonoma Water will obtain the building permit.
The design and permitting is expected to be complete by June and construction to start soon after. The work shouldn’t take more than four to six weeks, Mr. Roberts said. The goal is to have the system operational by the end of the year to meet grant requirements.