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.
(Colin Martorana, October 2020)
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.