Month: January 2021

San Mateo County faces a significant flood risk due to the concentration of developed areas within the floodplain and less developed areas that are subject to erosion. During major storms, many communities worry about nearby creeks rising quickly and overtopping, a problem that is exacerbated when tides are high and getting higher with sea level rise, and storms are more intense due to climate change. During storm events, like those this week, the need for clear and credible information so the emergency responders and the general public can make informed decisions has never been greater.

This is why one of the top priorities for the District during its first year was to expand and enhance the existing stream gauges in several of our most flood-prone waterways throughout the county. With a Statewide Emergency Response Grant from the California Department of Water Resources, this past fall, the District has focused on stream monitoring stations on Colma Creek, San Bruno Creek, San Mateo Creek, Belmont Creek, and Atherton Channel. Beginning with the storms in January 2021, these stations provide data on rainfall and real-time in-channel conditions so the District and our partners can estimate when and where flooding will occur in six cities and unincorporated areas of San Mateo County.

The process to determine each station’s location must strike a balance between being sufficiently upstream to provide ample warning to a downstream area subject to flooding, but sufficiently downstream to capture a significant portion of the watershed’s drainage area. It also can be advantageous to monitor water level over a particular window of time, especially where tides may influence flooding. This week, the District has also installed temporary gauges to work in tandem with the permanent ones to help calibrate the expected flows relative to rainfall and tides, so that we may better understand and predict the potential for overtopping and flooding.

Before this winter is over, we aim to build a webpage on our website, OneShoreline.org, that provides this information in a quickly accessible manner to the general public. And once the flood early warning webpage is fully operational, emergency personnel and the community can subscribe to receive flood condition notifications via text or email. The stations’ data may be used to inform the County’s SMCAlert network, and the page will serve as a centralized resource for live storm monitoring and preparation information throughout the county.

Stay tuned for updates on our project’s webpage here.

In late 2019 and early 2020, the cities of Burlingame and Millbrae completed separate efforts to analyze their flooding risk resulting from both sea level rise in San Francisco Bay (Bay) and precipitation from major storms. Within these studies, each developed and screened strategies to protect communities adjacent to the Bay shoreline and the major creeks that flow to it. Meanwhile, over the past several years, San Francisco International Airport (SFO) has developed a Shoreline Protection Program to protect the entire perimeter of the Airport from sea level rise.

Large areas of both cities (and the entirety of SFO) are projected to be inundated during the current FEMA 100-year event plus approximately 6 feet of sea level rise. Many regionally significant assets are located in this floodplain, including electrical distribution facilities, a regional commuter rail corridor and intermodal transportation center, regional water treatment plant, hazardous material sites, many major hotels and other businesses, U.S. Highway 101, and of course, SFO. In addition, other studies completed by San Mateo County explored flooding emanating from areas within Millbrae and SFO property affecting inland areas in the City of San Bruno (particularly, the Belle Air neighborhood) that were recently mapped into the FEMA 100-year floodplain. This project’s regional approach also allows for protection to these disadvantaged inland areas.

The District is partnering with the City of Burlingame, City of Millbrae, and SFO Airport to align, connect, and advance their efforts in a coordinated way, rather than each jurisdiction continuing to spend time and money on independent studies that cannot fully address this monumental regional challenge. Last fall, these project partners, with the City of Burlingame serving as the grant applicant, applied for federal funding under the new FEMA Building Resilient Infrastructure and Communities (BRIC) grant program to support the early steps in the project, including data collection, community outreach, and an alternatives analysis.

In the long-term, the project objective is to raise shoreline and creek bank elevations along 1.6 miles of Bay shoreline and 1.5 miles of creeks (shown in yellow on the figure below) to remove properties from the current FEMA 100-year floodplain plus approximately 6 feet of sea level rise – a Bay water level approximately 10 feet above today’s daily high tide.

In line with the District’s core principles, the project team will take a holistic approach to objectives by seeking to incorporate environmental, recreational connectivity, and community-building considerations into its evaluation of alternatives.