A notoriously flood-prone section of southern Marin could soon get its own defense against sea-level rise. Caltrans is proposing protections for the area along Richardson Bay between Marin City and Tamalpais Valley. The project would include the Manzanita Park and Ride lot and the Highway 101 interchanges at Shoreline Highway and Donahue Street. An online public meeting to introduce the plans is set for 6 p.m. Feb. 29. The webinar can be accessed at bit.ly/3ud2ovl. … The lower half of the Manzanita lot is closed an average of seven to 12 weeks out of the year because of frequent tidal flooding driven by sea-level rise, according to Caltrans. Intense rains coupled with high tides also flood the southbound Highway 101 offramp at the Donahue Street interchange in Marin City, O’Donnell said.