Samantha Weigel/Daily Journal
Severe erosion occurred during the recent winter storms near where the former Seymour Bridge was located in Half Moon Bay.
As the recent, and in many places record-setting, storms thrashed Northern California, Half Moon Bay is now faced with tough decisions on how it will manage one of its most precious recreational assets as it faces extreme erosion.
An extensive study of a mile-long strip of the California Coastal Trail found that if left unmanaged, areas could drastically erode up to 3 feet each year.
The City Council met this week to review studies of the Poplar Beach park area spanning between Kelly Avenue down to the Seymour Bridge. The council must soon decide how it will approach managing the site affected by naturally occurring bluff recession, as well as significant erosion caused by man-made problems including residential drainage and countless visitors who frequent the area for recreation.
The open space area is a popular destination for pedestrians, dog walkers, joggers, bicyclists, equestrians and the occasional foreign tourist bus dropping off sightseers. The coastal trail and surrounding park is a signature recreational resource for the city that’s heavily used year-round, said Jason Drew, a city-hired consultant with the firm Nichols Consulting Engineers
“It’s almost loved to death, that’s what’s happening,” Drew said, according to a video of the meeting.
The city must soon consider how to manage the area — which could include restricting access to certain areas as well as attempting to curb runoff — and how to realign the coastal trail.
Another area needing immediate attention is the Seymour drainage channel running through a cypress tree forest at the southern tip of the park. Following the recent winter storms, gully erosion was markedly exacerbated along the ditch where the city had only months ago moved a critical pedestrian bridge inland.
“It can be a bit shocking because you can actually be out in certain storm events and watch this thing move. It’s nature in motion,” Drew said, adding the new bridge the city just installed could be threatened if nothing is done.
The study is a comprehensive analysis of how the San Mateo County coastline is eroding in Half Moon Bay and is slated to continue with experts considering what types of policies — and related costs — could be implemented to curb degradation.
Options for the ditch range from temporary solutions like lining it with sandbags to more permanent fixes such as finding ways to divert the water, Drew explained.
There are also multiple severe erosion sites along the bluffs — which are sandwiched between the beach and a neighborhood of single-family homes, and runs between California State Parks’ Kelly Beach campgrounds and the Seymour ditch.
There are three main factors threatening the area. One is sea level rise and naturally occurring bluff erosion. There’s also surface erosion caused by water pooling and users packing the ground while veering off trails. And finally, localized bluff and gully erosion is exacerbated by drainage pipes carrying stormwater from uphill, Drew explained.
The area, which is also being studied as part of the county’s sea level rise vulnerability assessment, contains a county-managed former landfill — which erosion could threaten to expose.
Drew presented a few scenarios, one of the most extreme would be if the city did nothing to manage the area — which could result in sections where the cliff erodes 3 feet a year. Using timelines consistent with sea level rise models, by 2050 the coastal trail would need to be moved inland up to 120 feet in places; and by 2100, the trail could need to be moved up to 285 feet and potentially run into private property, Drew said.
A second scenario, in which the city does all it can to manage the site — including restricting public access, restoring and re-vegetating the land, erosion control and drainage improvements — would likely lead to about a 2 foot per year bluff erosion. In that, likely more expensive case, the trail would need to be moved inland up to 45 feet if it were to withstand sea level rise predictions through 2050, and 140 feet in places based on 2100 expectations.
Councilmembers noted they’d like to consider a hybrid option, but need more information about cost estimates before making policy decisions. Consultants and staff are expected to return in the coming months with more information.
One thing to be wary of is taking action that might divert the problem elsewhere, such as rerouting the stormwater or drainage to another part of the coast, Drew warned.
Vice Mayor Deborah Penrose urged officials to consider ways of reusing the water, particularly as a recycled water treatment facility is being planned on the coastside.
“I watch water running down the gullies, down the streets, it’s a crime,” she said.
Drew noted the high-profile nature of the site and potential recycling of water could make the city very competitive for grant funding.
One drawback is the city only has control of the estimated mile-long strip of coast as State Parks is responsible to the north and further south becomes private property near the Ritz-Carlton, said Community Development Director John Doughty.
After years of drought, Half Moon Bay, like many other communities still reeling from the winter’s torrential downpour, is hoping for a break.
“We’re certainly hopeful that the bulk of the rain and the activity this year has ceased,” Doughty said, noting emergency options could include temporarily removing the recently installed Seymour Bridge that serves as a critical connector to the coastal trail. “Weather holding, we should be OK. But there’s no guarantees.”
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