The centerline must be defined in a 1D-Hydraulic Centerline coverage and consists of a single feature arc that should start at the dam being modeled and end at or just after the last cross section. The centerline determines the extents of the simulation and helps to establish the stationing of cross sections that are defined along its length. You should create centerlines from the upstream (dam side) end to the downstream end in order to provide the proper direction to the model.
Related Topics:
Simplified Dam-Break Analysis
1D-Hydraulic Centerline Coverage
Cross Sections
Defining Roughness
Dam Properties