Lagoon pump failures intensified flooding in San Mateo

Initial findings from a consulting report on San Mateo’s New Year’s Eve storm response found multiple pump failures at the Marina Lagoon Pumping Station played a significant role in flooding, according to Schaaf & Wheeler, a consulting civil engineer firm.

During a July 18 presentation to the public at the San Mateo Main Library, city officials and Chuck Anderson with Schaaf & Wheeler told the public the city experienced mechanical pump issues like overheating at the Marina Lagoon Pump Station during the early morning hours between 5 a.m. and 8 a.m., with some engines failing and alarm alerts also not working during the storm. One of the five pumps at the station had problems all day. The city is still trying to determine the reason behind the pump issues. Anderson from Schaaf and Wheeler said pump operation remains one of the most important preventative measures for addressing flooding. Maximum lagoon levels were about 1 foot higher during the storm than they would have been had all pumps operated when required.

The storm flooded several areas of the city, particularly in the Shoreview and Marina Lagoon neighborhoods, causing extension damage and calls for a look into the city response and what can be improved. The calls led to the city commissioning a review by Schaaf & Wheeler of the events that staff will present at an Aug. 21 City Council meeting.

Analysis of New Year’s Eve conditions shows San Mateo also had some of the heaviest local rainfall totals during New Year’s Eve, with two particularly big spikes at night. The storm was greater than the Federal Emergency Management Agency 100-year design event used to establish the Marina Lagoon base flood elevation.

The city is looking to address future storm issues by fixing aging infrastructure, as current infrastructure and funding can be overwhelmed during rainstorms. 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 of the revenue needed for full improvements. The council is using the current number because it did not see the support needed for a higher fee in surveying done by a consultant.

Many residents have been vocal in asking for lagoon dredging to help with some of the risks. Public Works Director Azalea Mitch said dredging the entire lagoon would take two summers and cost around $80 million, with disposal costs and worst-case scenarios factored into an overall price based on a 2017 assessment.