Sediment transport, two-phase flow and loose boundary hydraulics are some of the problems of interaction between fluid flow (water or air) and boundaries that may be non-cohesive (alluvial) or cohesive. Unlike in classical hydraulics, these boundaries can change their shape and texture with changing flow conditions. Some of the material from the boundaries may be entrained into the flow, or sediment may be added to the flow, sometimes by tributaries as suspended matter. One instance is the transport of granular material in pipelines Since the changing boundaries are the central feature of most flow processes in nature, the term loose boundary hydraulics is here introduced.

Examines the physical processes involved in the interaction between air or liquid flow and the solid boundaries of its movement, showing how the properties of each material affect the dynamics between them.