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An ambitious plan to reduce flood risks for Palo Alto and Menlo Park residents near the Pope-Chaucer bridge is now on the verge of faltering after the agency overseeing the project concluded that the long-awaited replacement would actually endanger downstream areas.
The analysis, which the San Francisquito Creek Joint Power Authority board of directors discussed at a special meeting Thursday, June 8, represents a stinging setback for the agency’s plans in what’s known as “Reach 2” — the area between Newell Road and Pope Chaucer bridges. The creek authority had been planning to replace the Newell Road bridge and to widen the channel before commencing work on the Pope-Chaucer.
While the first two components of this plan remain on track, the new analysis from creek authority engineer Jack Xu is forcing the agency to reconsider its plans for the Pope-Chaucer bridge. The analysis concluded that unless the three cities along the creek — Palo Alto, East Palo Alto and Menlo Park — install flood walls along much of the creek, the risk to downstream areas such as University, Woodland and Euclid avenues would become significantly greater as a result of the Pope-Chaucer replacement. That’s because in its current configuration, the flood-prone bridge functions as a dam during storms, restricting flow to downstream areas.
“If Pope-Chaucer is in place, the communities on University and downstream will never see a flow higher than a certain amount,” Xu said. “When you remove that bridge, suddenly all the water gushes down and you’d have to protect those people from all the water that would come down if you remove the Pope-Chaucer.”
The agency began to revisit its assumptions about the hydrology of the volatile creek after the New Year’s Eve storm, which caused flooding near Pope-Chaucer and in other sections around the creek. Xu said the flooding during that event did not match what the creek authority’s modeling had predicted. The existing model, which was based on a 2009 analysis by a consultant, relied on data from four prior storms, all of which were less severe than the one that occurred during New Year’s Eve.
Xu’s report notes that the prior model had underestimated the “roughness” of the creek — a measure of vegetation, debris and other blockages that interfere with the creek’s flow. The prior analysis had also overestimated the capacity of the channel by as much as 2 feet in some area, the report states.
To protect downstream communities from increasing flood risk resulting from the Pope-Chaucer bridge’s removal, the creek authority would have to build flood walls 1,000 feet in length and 1 or 2 feet in height, depending on the level of protection that the agency would be seeking to achieve.
Given the findings, the creek authority is preparing to reopen some of the other flood-control alternatives that it had evaluated in the Environmental Impact Review for the “Reach 2” section of its plan. This will include, among other things, further evaluation of options for detention basins upstream.
Tess Byler, project engineer at the creek authority, said the recent analysis made it clear that the hydraulics at the creek have changed.
“That’s a shock to everybody,” Byler said.
Both she and Xu suggested that moving ahead with the Pope-Chaucer removal would be politically difficult, given historical opposition by property owners along the creek to having floodwalls installed along the creek.
“It would be very difficult to get a project where you can remove Pope-Chaucer,” Xu said. “It would take a lot of floodwalls. The history of the project shows there’s no appetite for that.”
‘When you remove that bridge, suddenly all the water gushes down and you’d have to protect those people.’
Jack Xu, engineer, San Francisquito Creek Joint Powers Authority
The news also came as a shock to the residents in Crescent Park in Palo Alto and the Willows neighborhood in Menlo Park, many of whom have been lobbying for the Pope-Chaucer bridge to be replaced since the major flood of 1998. Tom Rindfleisch, a Crescent Park resident who has been tracking the ebbs and flows of the flood-control project for years, said June 8 that many people in his neighborhood have trouble sleeping during rainy seasons because of flood risks. He challenged the creek authority not to abandon the project.
“There are going to be people who are really put out by this because of the continuing fear over the winter rain season on how they can protect their homes and their lives and their properties,” Rindfleisch said. “I believe the solution has to be get rid of Pope-Chaucer bridge and fix the downstream creek so it can hold the capacity for what will undoubtedly flow downstream.”
Menlo Park City Council member Drew Combs, who chairs the creek authority’s board of directors, shared his disappointment. Months ago, he had been telling residents in flood-prone areas near the creek that the long-delayed project would be finally coming, Combs said. He had also believed that the construction on Reach 2 would start before his term on the creek authority expires, a prospect that now seems less likely.
“This is a general frustration with the situation, but facts are facts. The science is the science,” Combs said.
Palo Alto Vice Mayor Greer Stone, who also serves on the board, urged the creek authority’s staff to consider possible mitigations that could improve flood control in case Pope-Chaucer is not replaced. He called the new analysis “concerning.”
“Some of the residents impacted by flooding there finally saw light at the end of the tunnel for that portion of the creek,” he said.
Given the latest findings, the creek authority plans to take a fresh look at other design alternatives, a process that will likely require additional analysis and will almost certainly delay the project even further. Board member Rebecca Eisenberg, who represents the Santa Clara Valley Water District on the creek authority’s board, urged staff to explore emerging technologies and other mitigation strategies to address flood control.
“Because the current situation is not tenable … It’s just not,” Eisenberg said. “The answer can’t be, ‘So sad. Too bad. Live with it.’ That’s not going to be OK.”
A new analysis by the San Francisquito Creek Joint Powers Authority has found that replacement of the Pope-Chaucer would send more water downstream, putting that area at risk of flooding.
I have lived near San Francisquito Creek since 1968 and used to swim in it as a Stanford graduate student. I bought a house on Oak Court off Woodland Avenue in 1975 because of the creek nearby. It is a magical and almost natural place that, most of the time, is good for the soul in its natural state.
I also attended the JPA meeting remotely. Several matters at the meeting and in the Almanac article troubled me:
1. “…flood walls 1,000 feet in length and 1 or 2 feet in height…”–Let us be very clear. What this really means is taking out all trees and all vegetation, and then creating concrete channels like the ones in south Palo Alto that were designed by Valley Water.
2. “…the hydraulics at the creek’s [sic] have changed.” Really? It seems that the creek has been flowing into the Bay for thousands of years. Is it possible that “climate change” has altered the creek? It seems far more likely that the engineers who built the model were wrong. However, blaming the problem on the creek or hydraulics theory makes me mistrust the engineers who are doing the analysis. Making a mistake is normal and excusable; finding a scapegoat for a mistake makes me distrustful of those who are suggesting it.
3. “The existing model…relied on data from four prior storms, all of which were less severe than the one that occurred during New Year’s Eve.”–While there was some flooding in late December, it was far less severe than the 1998 flooding even though the storm itself was more severe. I asked why that would be at the meeting and was told that the local jurisdictions had improved their storm-sewer capacities. This suggests that there are, indeed, other solutions to the problem that are more effective and possibly less costly than the $58 million replacement of the Pope-Chaucer bridge.
It is essential that we hear from more experts than those who have only concrete channels in their tool bag.
–Chuck Bernstein, 444 Oak Court, Menlo Park
Valley Water is showing that if Pope-Chaucer was replaced, their updated modeling (based on the actual water levels observed and documented durring the New Years Eve flood) shows that there would need to be 4 miles of 3 foot to 6 foot floodwalls from the Newell Street Bridge up to almost Pope Chaucer. 3 to 4 feet plus up to 2 feet additional on outside curves.
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Jack Xu, a Professional Engineer & Certified Flood Manager in the Valley Water Hydrology, Hydraulics and Geomorphology Unit, presented this conclusion in his June 8, 2023 presentation to the SFCJPA:
“Transfer of Flood Risk
Pope Chaucer cannot be replaced without a significant increase to the Reach 2 Proiect
• Floodwalls 3′ – 4′ for 2 miles on each side, from Newell Road up to almost Pope Chaucer”
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In Xu’s June 5, 2023 technical memorandum, he added:
CREEK SUPERELEVATION
Creek superelevation is a phenomenon that occurs when water flows around a bend in a creek.
The water on the outside of the bend moves faster than the water on the inside of the bend,
which creates a higher water level on the outside. There are areas on the outside of bends that
are shown to have flooded on NYE, but the revised models do not. Superelevation is not
considered in the HEC-RAS model and must be accounted for separately.
Using a simple methodology from the US Army Corps, an estimate for recommended
additional freeboard due to superelevation at various locations ranges from 0.75’ to just under
2.0’
Before the JPA abandons the Reach 2 flood plan, developed over many years of engineering studies and public discussion, I would like them to get an independent, expert opinion on whether the changes to the flood model are appropriate.
Mr. Combs was quoted as saying that “science is science” so we need to accept it. Environmental modeling is an approximation, not a science. Small changes in input variables can have major impacts on the results. According to their report, Valley Water made only one significant change to the 2016 flood model: they increased the “roughness coefficient” of the creek channel until the modeled 2023 flooding between Chaucer and 101 matched the actual flooding. That is, Valley Water has recalibrated the model to fit the 2023 flood, but has not validated the revised model based on previous floods. That needs to be done.
The report concludes that the roughness coefficient was too low because the original model lacked valid data on floating debris. This conclusion raises more questions than it answers, for example:
• Do you believe that the 2023 flood is typical what we will see in the future? Have you considered that the 2023 flood occurred after four years of drought, with many stressed and dying trees primed to fall?
• If floating debris is what caused flooding to exceed earlier predictions, wouldn’t it be less damaging to the creek environment (and less costly) to reduce debris by better maintenance of trees along the creek by cities and private landowners?
• Does the revised model account for the replacement of the Newell Street bridge? If not, the conclusion that removing the Pope-Chaucer bridge will increase flooding downstream is questionable.
I hope that the JPA considers these questions (and others) before making any decisions.