Crews have begun to place the final layer of concrete this week on the upper portion of the Oroville Dam spillway chute. This marks a “crucial milestone,” said Tony Meyers, project manager for the recovery project for the state Department of Water Resources, in a moderated media call on Wednesday. The top layer of the spillway consists of structural concrete slabs, which are designed to be erosion-resistant. The first two structural concrete slabs were placed Monday on the upper chute.