The Pope-Chaucer Bridge, which spans San Francisquito Creek and connects Palo Alto and Menlo Park, could be entirely rebuilt should a "preferred alternative" identified by the creek's governing body, the San Francisquito Creek Joint Powers Authority (JPA), come to fruition.

That proposal, analyzed as part of the JPA's newly released draft environmental-impact report, is one of a series of options to minimize the threat of flooding from the creek upstream of U.S. Highway 101.

In addition to a rebuilt bridge, the "preferred alternative" for reducing flood risk includes widening the creek channel in five locations and asking Stanford University to help, either by using its land to detain water upstream during major storms or by making changes to the Searsville Dam.

Other than the temporary noise and air-quality problems expected to arise during construction, the draft report concludes, the project's impacts would be "less than significant" if precautions and mitigation steps are taken, according to Len Materman, executive director of the JPA.

The creek, which is dammed at the Searsville Reservoir in the Jasper Ridge Preserve in Woodside, passes through unincorporated Portola Valley near Ladera and continues toward the Bay, running parallel to Sand Hill Road across El Camino Real. It then runs along residential areas, dividing Menlo Park and Palo Alto, with Woodland Avenue on one side and Palo Alto Avenue on the other. The creek continues along Woodland Avenue into East Palo Alto, passes beneath U.S. Highway 101 and continues into the Palo Alto Baylands and eventually end in the San Francisco Bay.

The Joint Powers Authority — which has on its board representatives from member cities East Palo Alto, Menlo Park and Palo Alto, as well as the San Mateo County Board of Supervisors and the Santa Clara Valley Water District — was formed in 1999 following a February 1998 flood that damaged about 1,700 properties. It was the worst flood since recording began in 1930.

Since its formation, the JPA has sought to reduce the creek's flood risk along three segments: the downstream section, running between the Bay and West Bayshore Road in East Palo Alto; a middle section, located from West Bayshore Road to the upstream side of the Pope-Chaucer Bridge; and an upstream section, from the bridge to the Searsville Reservoir.

Flood-protection work was recently completed on the downstream portion of the creek. The JPA built new levees and flood walls and created a new marsh flood plain, according to the report. Those efforts are expected to provide protection against the "largest possible" creek flows, while factoring in up to 10 feet of sea level rise above the average high tide.

The middle section

The creek's middle section is surrounded by the most residents and is most likely to flood, according to the impact study. If the Pope-Chaucer Bridge were to be replaced with one that can handle a greater creek flow and the creek channel were widened at five locations, the channel could handle a flood of the level seen in 1998, according to the report. Up to 7,500 cubic feet of water per second would be able to flow under the Pope-Chaucer Bridge and downstream, the report states.

Construction to replace the Pope-Chaucer Bridge would require it to be closed for about nine months.

To widen the creek channel, the JPA proposes to remove old concrete structures and replace them with vegetated, sloped banks. In places where restrictions limit the JPA's power to change the angle of the creek, it would install "soil nail walls" — a method of reinforcing the soil to hold it in place. This proposal would include the removal of invasive species of plants and the installation of water features like pools and riffles (rocky shallows) for fish, as well as "riparian enhancements."

There are also a couple of areas in East Palo Alto where the JPA could install small parks alongside the creek, according to Materman.

In addition, the report states, the temporary wall upstream of University Avenue would be replaced with a permanent concrete parapet that's about the same length and height. Just upstream, the concrete structure in the channel and wall on the East Palo Alto side of the creek would be removed and the riparian habitat installed.

According to Drew Combs, Menlo Park's City Council representative on the JPA board, a major goal of the JPA's work is to be able to provide the area protection from a 100-year flood event — a flood so bad it only happens once a century. That would require the creek and its adjacent infrastructure to be able to handle 8,150 cubic feet of water per second. Protection from a 100-year flood is the requirement for residents who want to skip buying flood insurance, which carries an average annual premium of $850 in California, according to a 2015 San Francisco Chronicle report.

To provide full protection from a 100-year flood, more has to be done upstream, according to the draft EIR.

The upstream section

Upstream of the Pope-Chaucer Bridge, the JPA explored the possibility of creating detention basins, where excess water could be held in a major flood event. Most of the creek in this section is on land owned by Stanford, "the largest landowner in the watershed," according to the report.

Stanford owns the Searsville Dam, which has been filling up with sediment over time. The university has been researching the possibility of making a hole in the dam to help clear out the sediment and permit fish to swim farther upstream. According to the report, Stanford has calculated that during a 100-year storm, such a project could reduce peak flows in flood-prone areas downstream by 800 to 1,000 cubic feet per second, beyond what the existing dam already provides. If Stanford doesn't move forward on that plan, the JPA may try to get on-site water detention basins built in other locations on Stanford property, the report states.

Water detention areas identified in the report include Stanford property as well as portions of the Webb Ranch U-pick field and parking lot and the former site of the Boething plant nursery, according to the report.

In addition to the downstream creek project that was recently completed, the Joint Powers Authority is working on the Safer Bay project, which aims to provide enough flood protection to properties along 11 miles of shoreline in San Mateo and Santa Clara counties to get them out of the flood plain and protect them against sea level rise.

Next steps

Three public hearings on the draft environmental-impact report will be held in late May and early June:

● On Thursday, May 23, from 7 to 8:30 p.m. at the Laurel School Upper Campus atrium at 275 Elliott Drive in Menlo Park.

● On Wednesday, May 29, from 7 to 8:30 p.m. in the East Palo Alto City Hall community room at 2415 University Ave. in East Palo Alto.

● On Wednesday, June 5, from 7 to 8:30 p.m. in the Palo Alto Art Center auditorium at 1313 Newell Road in Palo Alto.

Materman also plans to give presentations about the report to the Menlo Park and East Palo city councils on Tuesday, May 21.

The deadline to submit public comments on the report is June 19. Comments may be submitted by email to comments@sfcjpa.org or by mail addressed to: Kevin Murray, senior project manager, San Francisquito Creek Joint Powers Authority, 615-B Menlo Ave., Menlo Park, CA 94025. The JPA's phone number is 650-324-1972.

While review of the draft environmental-impact report continues, the JPA plans to seek funding through FEMA's hazard-mitigation grant program and the state's Proposition 1, as well as seek permits and land easement agreements. The original plan was to begin construction in 2020, but, according to a report Materman gave to the JPA's board April 25, "beginning construction in 2021 may be more realistic."

Access the full report here.

Related content:

• Crescent Park neighborhood resident Rom Rindfleisch discusses the efforts to prevent San Francisquito Creek from flooding on an episode of "Behind the Headlines," now available on YouTube.com/paweekly/videos, or our podcast page at PaloAltoOnline.com/podcasts.

• Plans finally emerge for replacing two north Palo Alto bridges

• Officials unveil first phase of San Francisquito Creek flood protection

• Stanford removes dam, giving endangered fish room to roam