More than five weeks after erosion damage at Lake Oroville forced residents to flee to high ground, the Butte County Sheriff’s Office on Wednesday announced it had lifted an evacuation advisory. More than 100,000 Butte County residents were given an hour’s notice to evacuate on Feb. 12, when officials feared that a concrete weir on the reservoir could collapse and send a 30-foot wall of water into the valley below. The order took residents by surprise because Department of Water Resources officials had repeatedly assured them that erosion damage to the reservoir’s main and emergency spillways posed no threat.