Bulldozers built giant sand berms Friday to protect beachfront homes in one of California's coastal cities hit hard this week by extraordinary waves generated by powerful swells from Pacific storms. Dozens of people watched construction of the emergency barriers in the Pierpont area of the city of Ventura, where a rogue wave on Thursday smacked spectators and vehicles as it overran the beach and flowed into a neighborhood. Eight people were taken to hospitals for treatment of injuries after the Pierpont incident, according to Ventura County authorities, who closed beaches, piers and harbors through Dec. 31. Similar waves overran beaches elsewhere Thursday on the California coast, flooding parking lots, streets and triggering evacuation warnings for low-lying areas. The ocean was less violent Friday but the National Weather Service warned that another round of extremely dangerous surf conditions would return Saturday. The Los Angeles-area weather office wrote that powerful cyclones over northern Pacific waters were sending 12- to 17-foot (3.6- to 5-meter) swells, creating “tremendous wave energy across coastal waters.” At some points along California, breaking waves were predicted to reach 25 feet (7.6 meters). Astronomical high tides were adding to a significant risk of more coastal flooding, forecasters said. “Overall, this is expected to be an exceptional high-surf and coastal flooding event that has not occurred in many years,” the weather service wrote. “Take caution and heed the direction of local authorities and lifeguards. Never ever turn your back to the water as damaging and life-threatening sneaker waves are likely to occur.” In Hawaii, which also was slammed by the huge swells this week, the weather service downgraded a high surf warning to an advisory Friday. Large breaking waves of 18 to 22 feet (5.5 to 6.7 meters) along some north-facing shores and strong currents will make swimming dangerous, the weather service said.