Floods are the most prevalent hazard in the United States and are considered events where people and property can be most adversely affected. Due to their frequency and proximity to occupied structures and residences, floods present the highest death rate of any natural hazard. Because Portola straddles the Middle Fork of the Feather River, and is confined in a river canyon, the City of Portola is at significant risk for flood damage, especially in low lying areas along the river.
The National Oceanic and Atmospheric Association (NOAA) stage gage on the Middle Fork of the Feather River near Portola, shows that the “action stage” of 7 feet has been exceeded regularly, and that the “flood stage” of 8.5 feet was most recently reached on 3/17/2011 with a stage of 9.03 feet.