With a wet winter predicted and more than $40 million in improvements said to be needed in Atherton's storm drain system, Atherton's City Council members attended a special meeting on Nov. 16 in hard hats, waterproof boots and safety vests for a first-hand look at some of the system.
The safety equipment came in handy as the council members started the tour by descending ladders into the Atherton Channel along Marsh Road near Bay Road at the town's border.
A recently updated master plan for the town's drainage system shows the Atherton Channel needs more than $4 million in work just so it won't flood handling the type of storm expected at least once every 10 years. Very little of that work will be done by this winter, partially because the state is delaying giving the town permits to do the work.
The drainage report, an update of a 2001 report, says that the channel currently can handle only a seven-year storm without the water overtopping its banks. Both reports were by San Jose engineering consultants NV5. To handle even a 10-year storm, the town would need to build detention basins to hold overflow water, which would be released gradually at a storm's end.
The report shows three possible locations for the detention basins, described as excavated areas that are filled with drain rock or have underground storage and are then covered over, often with turf. The locations are the playing fields at Las Lomitas School and Holbrook-Palmer Park and the polo fields at the Circus Club.
The town can't handle larger storms without regional cooperation, the report says, because much of the flooding danger is due to factors beyond the town's borders, including the size of the drainage channel the Atherton Channel feeds into.
Another problem, the report says, is that 49 percent of the water that drains through Atherton comes from outside Woodside, Stanford University land, Menlo Park, Redwood City and San Mateo County.
No one in the town seemed to know exactly when the Atherton Channel was built. The consultant's report says the town's drainage system was cobbled together in pieces starting when the first big estates were developed in the late 1800s.
The part of the Atherton Channel along Marsh Road has a concrete bottom with mortared stone side walls, some of them 9-feet high.
Even though the town cleaned the channel and made spot repairs along Marsh Road in recent months, some stones have fallen since then and many ornamental garden plants are growing from cracks in the mortar.
The town will repair the channel walls from Middlefield Road to Fair Oaks Avenue in Redwood City once it gets permits from the state.
Council, town staff and a couple of intrepid members of the public, including an Almanac reporter, hiked the channel from the town borders to Middlefield Road, where it becomes a large tunnel. A varied array of graffiti showed that others had been there before.
They continued in the tunnel under Middlefield Road to Watkins Avenue, where the channel returns above ground and is made of sprayed-on concrete.
The group climbed out past the railroad tracks on Watkins Avenue and continued to view some of the drainage projects completed since the 2001 version of the drainage plan, as well as to some of the system's current trouble spots.
The town has completed 26 of the 55 projects identified in the 2001 study, including improvements the council viewed in the Barry Lane and Elena Avenue area.
Other areas viewed included a spot near Las Lomitas School on Alameda de las Pulgas where in 2012 the channel was overtopped and the school flooded and the spot where the Atherton Channel begins near the western end of Walsh Road.
The drainage study prioritizes the work, with the first priority nearly $6.14 million in projects that it says are "life and safety issues." Those projects include relining the San Francisco water line and Reservoir Channel in the Walsh Road area west of Alameda de las Pulgas, upgrading the existing channel at Alameda de las Pulgas and Camino al Lago, and re-lining the Atherton Channel west of Alameda de las Pulgas.
Next are projects needed to "avoid damage to private property," estimated at $8.6 million. The third priority, public improvements not affected by the downstream drainage outside the town, would cost $3.2 million.
Public improvements that are affected by the downstream drainage are the biggest cost $23.6 million. The lowest priority are projects recommended in the 2001 study that don't seem to have current issues, estimated at $3.6 million.
Atherton has $910,000 budgeted for drainage improvement projects this fiscal year, and $3.625 million budgeted over the next five years. The town is also working with the Las Lomitas school district to possibly build a detention basin at Las Lomitas School.
To prepare for the predicted winter storms, city employees have walked the entire Atherton Channel and made sure all town storm drains and drainage ditches are not blocked. There are 2,500 sandbags and the sand to fill them in the town's corporation yard, near the railroad tracks south of the Caltrain station.
The council members visited several problem areas the town will be keeping an eye on this winter, including the Bellbrook Culvert in the Walsh Road area west of Alameda de las Pulgas, another place the town is waiting for a permit to repair. They also walked along the ditch running behind back yards on Parker and Euclid avenues, which town crews recently cleaned and the town will be monitoring.
The town also plans to monitor problem areas along Laburnum Road and Magnolia Drive in Lindenwood.