The head of California’s water agency on Tuesday repeated his assertion that an emergency spillway at the Oroville Dam worked, drawing an incredulous response from a state lawmaker who represents tens of thousands of people ordered to evacuate when it was feared erosion at the spillway could lead to catastrophic flooding. Bill Croyle, acting director of the Department of Water Resources, faced lawmakers for the first time since the evacuations in February. Authorities feared a concrete wall at the top of the emergency spillway was on the verge of collapsing and sending a wall of water rushing uncontrolled through downstream communities.