A number of uncontrolled tributaries entered the Willamette upstream of the city, and many experts predicted that the crest would top Portland's floodwall, which protected the downtown area. In response to this threat, Portland's mayor Vera Katz requested technical assistance from the Corps and asked for volunteers to help city crews reinforce the wall. In a matter of hours, the riverfront teemed with people filling sandbags, building a higher plywood wall, and reinforcing the plywood with concrete road slabs.