Fixed, for now

San Mateo County officials say they inspected Ox Mountain in the wake of flooding on Highway 92 and that erosion from the landfill did not cause the problems experienced last week. Clay Lambert / Review

Last week’s atmospheric river brought a brief but torrential downtown to Half Moon Bay and unincorporated parts of the Coastside, flooding roadways and leaving officials thinking about how to improve local drainage systems for the next round of storms, which have already rolled into town.

On Highway 92, flooding from a swollen Pilarcitos Creek washed across the roadway and swamped La Nebbia Winery on Dec. 13. The winery, which announced last week it would remain closed through the end of the year and possibly into 2022, said it needed time to repair its damaged outdoor patio space.

At nearby Ox Mountain Sanitary Landfill, which is run by Half Moon Bay’s waste management contractor Republic Services, officials said that the flooding on Highway 92 was the result of debris from Corinda Los Trancos Creek, a 1.5-mile tributary to Pilarcitos Creek. The debris reportedly clogged a culvert operated by Caltrans. Caltrans, which had a crew on the scene Monday morning, did not immediately respond to requests for comment.

Staff from San Mateo County Environmental Health Service’s Solid Waste Inspection Program, which regulates the landfill operations, visited the Ox Mountain Landfill several times last week to assess the erosion and possible contamination caused by the rain, according to Heather Forshey, program director. The county reports minor erosion from the rain, but not to the extent that it contaminated Pilarcitos Creek.

Reports of localized flooding in and around Half Moon Bay during the storm earlier this month go well beyond flooding on Highway 92. Half Moon Bay Public Works Director John Doughty said staff is examining its drainage system capacity where flooding occurred last week, including at Railroad and Miramontes avenues, and on Golden Gate Avenue in between Highland and Silver avenues. Doughty acknowledged that these areas have repeatedly had drainage issues during major storms and that the city’s stormwater system was overwhelmed by last week’s weather.

“This was a large and unusual storm, even in the world that we’re looking at with the potential for these types of storms more often,” he said.

Doughty noted that last week’s torrential downpour was shorter but more intense than October’s atmospheric river that set record rainfall levels around the Bay Area. The National Weather Service reported on Dec. 14 that Half Moon Bay received 4.87 inches of rain over the previous 72 hours. The city’s average rainfall for December is 5.17 inches, according to Golden Gate Weather Services.

“Clearly, our drainage and stormwater system was overwhelmed,” Doughty said. “It was not ever designed, nor would we probably ever design for that type of storm, because you just can’t afford to do that.”

The city’s blueprint for managing stormwater comes in the form of the 2016 Storm Drain Master Plan Update, which determines how stormwater capital improvement projects should be created and funded. Doughty said over the last several years the city has been slowly transitioning from the plan’s first phase that identifies issues and infrastructure to the second phase that delves into costs and implementation.

Half Moon Bay’s Capital Improvement Program that was adopted in June forecasts the city will spend $11.3 million on stormwater projects in the next five years, including in the Kehoe neighborhood and with Seymour and Roosevelt ditch improvements. It states that there is a $9.5 million shortfall between funding and necessary expenditures, with the Kehoe neighborhood project accounting for the bulk of that gap. The estimated cost of that project alone is $7.8 million over time.

“It’s hard because some of these projects will take many years to get to the point of permitting, and then we have to figure out funding,” Doughty said.

Doughty noted that the city is dealing with infrastructure installed over the last five decades, and there are regulatory challenges from agencies that want to transition away from “gray” infrastructure, like pipes or tunnels, to “green” infrastructure that utilize plant or soil systems to manage stormwater. Doughty said if there was enough support, one option could be for neighborhoods to form a Benefit Assessment District. It’s a mechanism for residents to pay back loans or bonds along with their property taxes to fund public improvements and services.

Doughty said that ultimately, major upgrades will require a cost-benefit analysis from city officials and residents. If these types of stronger weather events become more common, the city government and local communities will likely have to weigh how much to spend on dependable drainage.

“If the predictions continue to play out with more frequent higher intensity and shorter duration events, obviously we’ll have to look at those in light of the changing environment,” he said.

August Howell is a staff writer for the Review covering city government and public safety. Previously, he was the Review’s community, arts and sports reporter. He studied journalism at the University of Oregon.

(3) comments


It may not have been reported in this paper, but the SAM plant had flooding which hampered some operations, but the plant made it through by shutting off flows from the north, using the Intertie Pipeline System and Wet Weather Storage (incl. 200kgal just added this past year), while HMB alone used the plant, right up to its limit. Two points stand out: A) this points to the Lie that is HMB's lawsuit vs. SAM, clearly it received benefit, once again, from this longstanding design, and B) HMB STILL has no wet weather storage of its own and is leeching off the investments perceptively made by its upstream partners in MWSD and GCSD.

It's hard to make a definitive statement without thorough study, but it sure looks like HMB would rather have a library it can't pay for than working infrastructure it will sue to not pay for...


"Wasn't me, it was THAT guy!"

Said no innocent person ever.

August West

So you have proof it was the landfill? Please do share.

Welcome to the discussion.

Keep it Clean. Please avoid obscene, vulgar, lewd, racist or sexually-oriented language.
Don't Threaten. Threats of harming another person will not be tolerated.
Be Truthful. Don't knowingly lie about anyone or anything.
Be Nice. No racism, sexism or any sort of -ism that is degrading to another person.
Be Proactive. Use the 'Report' link on each comment to let us know of abusive posts.
Share with Us. We'd love to hear eyewitness accounts, the history behind an article.

More Stories