San Mateo releases full storm report

The report noted the event was a double-barrel storm, meaning there was a significant period in the early morning followed by a calm before a second intense period. The first period is when the pumps failed, with the backup pumps not immediately called to run after the engines failed, according to the report. The ultrasonic sensor that measures water levels stopped reading at 97.2 feet, while several engine alarms did not alert city staff of problems.

Engine failures early on prevented the Marina Lagoon level from being drawn down during the break between the rainfall peaks and resulted in the Marina Lagoon level rising to a peak of 98.4 feet, according to the report. If the pumps had worked, it would have been around 97.4 feet, within the original pump station design parameter of keeping levels below 98 feet. Debris also contributed reducing flow to the pumps.

Flooding in the Sunnybrae neighborhood and Laurel Creek just upstream of George Hall Elementary School was due to local capacity deficiencies, not the elevated Marina Lagoon levels, according to the reports.

Areas near San Mateo Creek and Marina Lagoon saw extensive flooding and damage at the turn of the New Year, with San Mateo expecting around 1 inch of rain but getting about 5 inches on New Year’s Eve. The damage to many neighborhoods and property led to renewed residential calls for more city action to help in the storm’s aftermath. San Mateo typically gets around 22 inches of rain each year.

According to a staff report, areas near Arroyo Court, the Sunnybrae neighborhood, Borel Creek, San Mateo Village and Laurelwood Park saw flooding. The city also saw its sanitary sewer system overwhelmed with rainwater, causing diluted wastewater to spill into the streets. The response from the city drew criticism and calls from the community for a look into the city’s response and led to the report.

The city is looking to address future storm issues by fixing aging infrastructure, as current infrastructure and funding can be overwhelmed during rain storms. Potential ways to address the issue, like citywide infrastructure improvements, would cost around $68 million. The city wants to have an $8 monthly stormwater property fee to maintain operations of the city’s stormwater system. The fee would require property owner approval through a citywide ballot measure in November. It would be included as an annual property-related fee in perpetuity on a property tax bill. However, it is still less than half the revenue needed for full improvements.

People can go to https://sanmateo.primegov.com/Portal/Meeting?meetingTemplateId=6885 to find the full report. The council meeting on the subject is set for 7 p.m. at city hall.