A one-dimensional mathematical model for the development of an exudated layer and macrosegregation near a cast surface is established. While forced convection leads to a highly segregated layer at the surface of the casting and a solute depleted zone near the surface, solidification shrinkage induced flow makes the negative segregation within the casting less pronounced. Parameter studies reveal that the heat transfer coefficient for chill contact, the metallostatic head, and the criterion for onset of exudation, all have a major influence on the resulting macrosegregation. The mathematical model is used to estimate macrosegregation development in the direct chill casting of an Al-4.5% Cu rolling slab. It is found that both forced convection and shrinkage-induced flow have a significant effect on the macrosegregation near the cast surface.