First guess: depends on what you mean with "negligible". The velocity distribution will depend on many factors, including inlet velocity, fluid properties (density, viscosity, solid concentration) and the geometry of the system itself. An approximate solution may be provided by free stream calculations, but slurries may be to complex to give accurate solutions from this approach. Furthermore, there must be an outlet for mass conservation - so the slurry must get there somehow (i.e. it must have a certain velocity). What is the meaning behind your question?

Best,

Stephan