By 2100, the sea water that surrounds the San Francisco Peninsula is expected to rise anywhere from 17 to 66 inches, according to projections by the National Research Council. Just what is at risk in San Mateo County should that happen is the subject of a lengthy study by the county's sustainability office.

The report looks at infrastructure and properties throughout the county along the Bay and coastal fronts and evaluates how they might be affected under three potential scenarios: a baseline estimate of a 100-year storm at a higher water level, a mid-level estimate of a 100-year storm plus 3.3 feet of sea level rise, and a high-level estimate of a 100-year flood plus 6.6 feet of sea level rise.

The study found that under present conditions, property totaling $1 billion in assessed value is vulnerable to flooding across San Mateo County. That number rises to $39.1 billion in assessed value for areas vulnerable to flooding and erosion under the high-level scenario of predicted sea level rise over the next 50 to 100 years.

Not surprisingly, the areas most at risk are those at the lowest elevations closest to the Bay and properties along the coast. The study did not look at areas that are not expected to be directly exposed to sea level rise, like Atherton and Woodside.

According to Hilary Papendick, the county's climate change program manager, the estimates "likely underestimate the total value of all the assets we care about."

Jurisdictions that are inland from the Bay could still be affected by sea level rise if key infrastructure along the Bay is flooded. Electricity, wastewater and road infrastructure clustered near the Bay that serve people living at higher elevations could have far-reaching impacts if flooded.

Menlo Park

Damage to property in Menlo Park alone could total between $182 million and $1.62 billion in assessed value, according to the findings of the vulnerability assessment. Those risks are primarily borne along the Bay side of the city, where some of the city's more vulnerable residents reside. The study defines vulnerable communities as being lower income; having fewer people who speak English well; having residents who don't have cars, or who spend a disproportionate amount of their income on housing or transportation; or having a high number of elderly or very young residents, or residents who lack a high school diploma.

It's also the area of the city where Menlo Park has agreed, with the City Council's November 2016 approval of the general plan update, to allow 2.3 million new square feet of nonresidential development, 4,500 new housing units, and 400 hotel rooms.

The study details Menlo Park's potential vulnerability related to sea level rise as follows:

● Under the baseline scenario: $182 million in assessed property values; 2,006 acres of land; fewer than 100 people, many of whom are in vulnerable communities; two miles of storm drains; five miles of transmission lines and five transmission towers; eight salt ponds and crystallizers; 2.6 miles of trails; 0.2 miles of local roads.

● Under the mid-level scenario: $1.29 billion in assessed property values; 2,874 acres of land; about 2,800 residents, all of whom are in "vulnerable" communities; 11 miles of local roads; 11 miles of storm drains; two outpatient health care facilities; five parks and eight miles of trails.

● Under the high-end scenario: $1.62 billion in assessed property values; 3,037 acres of land; 4,300 residents from vulnerable communities; 15 miles of local roads; 12 miles of storm drains; two outpatient health care facilities; five parks and 10 miles of trails.

Vulnerable neighbors

Menlo Park's immediate neighbors along the Bay -- in East Palo Alto and along the unincorporated area of Redwood City where a number of mobile home parks sit -- also face severe losses should sea level rise.

The study lists East Palo Alto's potential vulnerability as follows:

● Under the baseline scenario: $171 million in assessed property value; 335 acres of land; 2,400 residents -- all of whom are considered "vulnerable"; 215 acres of wetlands; 4.3 miles of local roads; 2.1 miles of storm drains and one stormwater pump station; four hazardous material sites; two emergency shelter sites; one electric substation; 1.5 miles of shoreline; 0.4 mile of natural gas pipelines.

● Under the mid-level scenario: $631 million in assessed property values; 714 acres of land; 7,600 "vulnerable" residents; 230 acres of wetlands; seven emergency shelter sites; 39 hazardous material sites; 5.3 miles of shoreline; 14.6 miles of local roads; four miles of storm drains; 1.4 miles of transmission lines; nearly a mile of natural gas pipelines.

● Under the high-level scenario: $975 million in assessed property values; 992 acres of land; 12,700 "vulnerable" residents; 231 acres of wetlands; nine emergency shelter sites; 44 hazardous material sites; 22 miles of local roads; 6.4 miles of shoreline; six miles of storm drains.

Access the full report here.

In addition, the mobile home parks on East Bayshore Road -- next to Bayfront Canal and the Cargill salt ponds -- could face a total loss of $19 million under the baseline scenario. All people living there would be affected, as would all of the levees, flood walls, roads, storm drains and transmission lines just over the Menlo Park border in unincorporated Redwood City.

Boosting resiliency

"When we think about planning for sea level rise, we think about defensive structures, whether that's levees or wetlands," said San Mateo County Supervisor Dave Pine in an interview. "But we also need to think about land use policies."

"Historically, our county is very aggressive building into the Bay shore, and that's why we have so much at risk with the rising sea," he said. "The idea of retreating from the Bay shore is not likely to happen in the foreseeable future."

According to the county report, one variable is the extent to which the wetlands will provide a barrier against sea level rise.

There are a number of ongoing projects along the Bay to provide protection against flooding. The South Bay Salt Pond Restoration Project is an ongoing initiative to restore wetland habitat in the Ravenswood Pond complex along the Bay in Menlo Park. So far about 240 acres have been restored with a 155-acre pond.

There are also plans to breach the outermost pond and restore the tidal marsh along the Bay and improve the levees.

Menlo Park is also taking steps to rebuild its wastewater pump station, one of the pieces of the city's infrastructure considered to be vulnerable to sea level rise. Last May, the council agreed to budget $6.2 million to improve the city's pump station and move it to a higher elevation, still near its current location at 1221 Chrysler Drive, near the intersection of Chrysler Drive and Bayfront Expressway. The project received $500,000 from the Bohannon Development Corp., which is designing and building the exterior of the pump station in an artistic geometric shape to align with phase two of the company's planned Menlo Gateway development.

Another project, currently in the design phase, is to reroute the Bayfront Canal into the South Bay Salt Pond Restoration project, allowing floodwater to be stored and mitigating flooding at the mobile home parks on East Bayshore Road, according to a statement by Redwood City. The project is led by San Mateo County and supported by the cities of Redwood City and Menlo Park and the town of Atherton. Construction is expected to start this fall or in the spring of 2019.

San Mateo County, along with the City/County Association of Governments, hosted a March 30 conference at Canada College about water management and how to address the threat of sea level rise. Elected officials encouraged people to work together to pursue funding for big infrastructure projects.