Dredging removes sediment from the river beds mechanically. These processes can introduce system feedback (e.g. inducing deposition) and often must be modeled explicitly, because transport and continuity equations cannot account for anthropogenic processes. Therefore, HEC-RAS includes dredging capabilities, with multiple methods to incorporate dredging into sediment simulations. Go to Options menu of the Sediment Analysis Editor to find the Dredging Events Editor. HEC-RAS 5.0 includes several new dredging features.
Create a Dredging Event by pressing the New Dredging Event button: 
A dredging event removes sediment from a cross section or cross sections at the Dredging Start Time or between the Dredging Start Time and Dredging End Time. Simulate complex dredging configurations or recurring dredging schedules over an extended simulation by defining multiple Dredging Events.
Select a Method for each Dredging Event. There are seven dredging methods, including two basic types: Elevation (the first three) and Mass (the last four).
This video describes the basic, elevation dredging features.