The Greenwood Arch

The Greenwood Arch
The Greenwood Arch

Fifty or so Valleyites showed up last Wednesday evening to look at the to-be-replaced Philo-Greenwood Road bridge. The first-hand walk-through at the bridge was followed by a presentation by three engineers from Quincy Engineering (Sacramento) at the nearby Bates Apple Farm, easily the most attractive site possible for a public meeting.

The entire neighborhood of the Apple Farm, Hendy Woods, the Navarro River, and the stately old one-lane bridge traversing the river is one of Anderson Valley's most precious vistas, hence the public's determination that the replacement bridge be as practically and as aesthetically consistent with the area as the old bridge has been all these years.

Howard Deshield of Mendocino County's Road Department was also on hand since the bridge project and the County road at both ends of it are County responsibility, although Caltrans and the feds have the final say because they control the pursestrings.

The good news is that the old bridge may not have to be replaced at all, just beefed up and widened. The bad news, if it is bad news, is that the bridge will have to be widened, and both the feds and Caltrans will have to sign off on it.

In August of last year the same engineering team made a preliminary presentation at the Boonville Firehouse about the need to do something about the old bridge before it collapses. They also pointed out that the existing bridge is “functionally obsolete” because it’s narrower than the roads it serves at either end.

At the earlier meeting, the engineers convinced some bridge replacement opponents — some locals were clearly in favor of replacing the old bridge — that something needed to be done and whatever it was, if it was going to be federally funded, it was going to have to be wider and, as all federal projects, especially those requiring a Caltrans sign-off, disproportionately large and a huge, soul-destroying affront to the human spirit.

Lots of people told the engineers  that whatever they did, the Valley wanted to keep the graceful arch structure which holds up the larger half of the bridge over the Navarro. At the firehouse meeting, the engineers didn’t think the old bridge could be saved. The other half of the bridge — the “approach structure” near the Apple Farm — is made of aging timbers and there’s no debate that it should be replaced before it collapses.

At the outset of last Wednesday’s meeting, the engineers — Project Manager James Foster, road and traffic engineer Jason Jurrens and structural engineer Max Katt — proudly announced that they had come up with a way to keep the existing arch by simply duplicating it (with new design standards and materials ) and attaching it to the old one. This would not only provide the necessary lateral-seismic stability — the existing arch is fine with vertical loads — but would bring the bridge up to modern standards which the feds will probably fund.

Their design is simply boffo!

After reviewing the existing concrete and steel arch structure and its footings, most of it built in 1951, the engineers concluded that the old bridge “has good bones,” and “it’s in good shape for as old as it is.” They also decided that whoever picked that particular place on the river for the bridge (a decision that was made in the last quarter of the 19th century),  had picked the perfect spot on the Navarro with solid bedrock on both sides which is also large enough to anchor the duplicate structure on the downstream side.

According to roadway engineer Jason Jurrens, the County's traffic study concluded that there are about 420 vehicles crossing the bridge every day, much of that probably back and forth to Hendy Woods State Park on the west side of the bridge. Traffic at that volume means no exemption from federal width standards.

To retain the arch and widen the bridge, four phases of construction over two years will be required so that one-lane traffic can continue to use half the bridge while the other half is built or upgraded.

The engineers also looked at building a conventional bridge a couple hundred yards downstream which would be a standard neo-Stalinist Caltrans-style overpass concrete job with one central pillar. While meeting the federal specs, this alternative is not only unattractive, but it would require acquisition of new right of way and much more in the way of environmental mitigation. It's so totally not viable as to be insane — so we can't rule it out yet.

The design team estimated that either option would cost in the neighborhood of $5-$6 million to build. The Caltrans style overpass would undoubtedly be more costly than the double-arch existing bridge upgrade when right of way and environmental costs are added to basic construction costs.

Several members of the audience were still opposed to widening the bridge — total width would go from 17 feet to about 37 feet including shoulders and a five-foot wide sidewalk. The Philo-Greenwood Road is upwards of 24 feet wide and a narrow two lanes at present.

In response to the bridge widening opponents, County Transportation Director Howard Deshield said that his data shows that most traffic accidents occur because of impaired or distracted drivers, and that a wider road surface would improve traffic safety because it would give drivers room to maneuver or recover if they suddenly needed to.

Philo resident Jean Duvigneaud somewhat jokingly suggested, “Why don’t you go ahead and build the wider bridge, then just block off one lane?”

Engineer Foster laughingly replied, “Now that is thinking outside the box!”

But Deshield disagreed: “As someone who has tended many gates around this county, I can assure you that within 24 hours whatever blockage you put up would be gone.”

Deshield and Foster both pointed out that not doing anything and leaving the bridge as is would put a major and increasing maintenance burden on the County because the timber approach structure, especially, is in very bad shape and getting worse.

In the end, most people seemed happy with the engineers’ method of saving the arch. The engineers seemed to have listened to what most locals wanted, although a few are still clearly unhappy about the prospect of a wider bridge which they think will encourage unsafe speeding.

In the next few months the engineers plan to do more detailed engineering and analyze the environmental impacts of the two alternatives. Then they will present those alternatives to Caltrans and the feds — with their recommendation that the double-arch version is preferable and meets all specs and standards — and is probably cheaper.

If things go as planned, construction is expected to begin in 2016, although as both Foster and Deshield admitted, “consultants are always optimistic.” ¥¥

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