The term baffle covers a flat board or plate, deflector vanes, guides, grids, gratings or similar devices constructed or placed in flowing water, wastewater or slurry systems.
A baffle is used to absorb energy to slow the flow or to produce a more uniform distribution of velocities. It can divert, guide or agitate the liquid, and it can check eddies.
In the picture the baffle is used to avoid the inlet water activating the float switches. It also minimises the mix of air in the water as it splashes in to the pumping station.