DEL MAR — Sea-level rise is an ever-present concern in a city like Del Mar, aggravating the city’s fragile bluffs, raising the stakes for oceanfront homeowners, and now — prompting weariness over a potential replacement bridge to be built at North Beach.
At an April 1 City Council meeting, council members expressed concern about how the 600-foot-long Camino Del Mar bridge passing over the San Dieguito River mouth might contest with sea-level rise projections.
Plans to erect a new structure have been in the works for several years, after a 2012 evaluation study determined the current bridge is deteriorated, and subject to washing out or collapse in the event of a flood or earthquake.
The study also found that the bridge’s 11 supporting spans were restricting river flow.
Discussions on what the bridge will look like and how it will be built are still preliminary — though early drawings reveal the structure will have a vehicle lane going in each direction, a 7-foot median, and walking paths and bike lanes going in both directions.
The new bridge would stand on six piers.
The project’s consultant, Kleinfelder, Inc., is currently looking to increase the new bridge’s height by 2 to 3 feet, in order to clear the projection of five and a half feet of sea-level rise by 2100. The bridge is anticipated to last 75 years.
Some council members worried that three feet might not be enough. Councilman Dwight Worden asked if it’s possible the bridge could be raised a little bit higher.
“I’ve just seen so many sea-level rise projection numbers, that you tell me we’ve got five inches before our bridge is wet, I’m nervous,” he said.
Thiele said the bridge will be designed to keep the deck dry during a flood scenario. He added that even in the case that waters do flow over the top of the bridge, the structure will be strong enough to endure it.
Councilwoman Terry Gaasterland cited a 2013 San Diego Association of Governments report that highlights “adaptive management strategies” for bridges — such as designing structures that can be raised in the future to adapt to higher water levels.
However, such a route would involve a precast system — which the consultant said would be challenging for the bridge’s location.
Thiele and the consultant recommended a cast-in-place option for building the bridge — similar to the structure of the bridge at Los Penasquitos Lagoon.
According to City Engineer Tim Thiele, this would help limit the construction “footprint” by reducing the number of necessary staging areas and allow for more flexibility in the bridge’s form.
Thiele said consultants will continue to “(play) the balancing game” — planning for a bridge that is high enough to adequately compensate for sea-level rise projections while still being compatible with the levels of the adjacent roadway.
When it comes to construction, council agreed that a staged construction scenario that would maintain a flow of traffic along the bridge would be the best way to approach the project. The option would take 24 to 27 months rather than the 13 to 15 months anticipated if the road would be entirely closed off.
Demolition and construction would occur on one side of the bridge first, then switch to the other.
This option was supported by residents at an open house workshop in January, where attendees raised concerns over emergency response times to the Beach Colony neighborhood.
During the public outreach process, residents have also suggested an unplanted median, installing overlooks on one — if not both — sides of the bridge, and perhaps buffering the bike lanes.
The project is currently in the project approval and environmental documentation stage. At the meeting, Thiele anticipated the project would go to the California Coastal Commission and Design Review Board for approval around 2021-2022. He estimates the city will be able to go out to bid for construction between 2023-2025.
At the meeting, council approved 5-0 a second amendment to the city’s agreement with Kleinfelder, Inc. to continue collecting preliminary data. The amended contract is for about $1.6 million.
According to the April 1 staff report, the project is anticipated to cost about $22.7 million, with over 88% of the funds to be covered by a Federal Highway Bridge Program grant.
