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After Las Lomitas Elementary School faced flood damage from the winter 2023 storms, school officials said a flood mitigation plan was necessary to protect the Atherton campus at 299 Alameda de las Pulgas from future creek flooding.
Mike Wasserman, owner at Capital Program Management, Inc. and Jason Mansfield, civil engineer with BKF Engineers presented the school board with a long-term flood mitigation plan on Wednesday, April 17.
In March, Rep Anna G. Eshoo, D-Menlo Park, announced that she was able to secure about $1.4 million in funding to address flood mitigation in Atherton. Superintendent Beth Polito plans to meet with Atherton’s mayor, Diana Hawkins-Manuelian, in May to discuss their partnership and future plans for flood mitigation.
“I’m proud to have secured funding for the Upper Atherton Channel Flood Mitigation Project which will increase the capacity of the channel and reduce flooding during major storms,” she said in the press release. “This project is critically important because storm flows overtopped the channel two years ago, causing the closure of Alameda de las Pulgas and the flooding of classrooms at Las Lomitas Elementary School.”
Over the winter, the school took preventative measures against heavy rainfall by adding grates on campus to capture rainfall, according to board member Jason Morimoto. During the heavy storm season in February, the creek luckily didn’t flood as it did in January 2023 and the campus did not see any damages. Moritomoto said that the town of Atherton made sure to clear the debris in the culverts early this year.
The upstream drainage area encompasses 1,200 acres involving the jurisdiction of Woodside, Atherton, Menlo Park, San Mateo County and Caltrans. All of this drainage flows straight toward the school campus.
“We’re looking at a lot of water coming down and it being blocked by the school,” Mansfield said.
Mansfield said possible solutions for the school could include reducing flows upstream, creating an alternative flow route and capturing and storing water on-site.
Currently, the school’s property lies on top of culverts, which channel water underneath the campus. These culverts have a limited flow capacity that has no ability to withstand more.
Debris buildup is also an issue in these culverts, which clog the drainage and send overflowing water toward the school.
“There’s already work to clean up the channel and line up the creek,” Mansfield said. “If we can reduce the amount of debris coming down the channel we can utilize the culverts coming through.” He adds that adding a trash rack at the culvert opening can allow increased flow for full capacity.
Evaluations showed that possibilities for the infiltration and storage of water underneath the campus would be too expensive and would not provide “value or relief to the school.” Any solutions will have to be compatible with the school’s uses and so infiltration systems under well used areas of the school such as the parking lot and ballfield would not work.
Final recommendations in the presentation touched on adding infiltration and detention upstream, dry wells and basins in the creek, and considering diversion options.
School board member Laura Moon asked: “Are there other entities beyond individual homes that are within the [drainage flow] that are in a similar situation or is this something uniquely ours to deal with?”
Mansfield responded saying, “it is very unique to have culverts running through your property or under buildings,” making Las Lomitas’s situation special.
“I look forward to the partnership with the town of Atherton in terms of working through ways to mitigate the creek and culvert for future rainfalls,” said Morimoto after the presentation.
Next steps for the plan will be to develop a maintenance plan, study flood mitigation measures in upper watersheds, present and develop solutions with agency jurisdictions, identify additional funding, design and implement.
Wasserman said that he is working with the town for a FEMA grant which has started to get some movement. The grant will provide funds for a creek monitoring system, overflow box culvert under the creek and on campus retention.
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