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Erosion is a process that involves the detachment of soil particles from within the soil surface FOLLOWED by the transport of these detached particles away from the site of detachment.

.	1.	Raindrop Detachment with transport by Raindrop Splash
.	2.	Raindrop Detachment with transport by Raindrops interacting with Flow
.	3.	Raindrop Detachment with transport by unassisted Flow
.	4.	Flow detachment with transport by unassisted Flow

1. Raindrop Detachment with transport by raindrop splash
When erosion is driven by the energy derived from raindrops impacting the soil surface, raindrop energy is used to overcome the bonds that hold particles in the soil surface and may also be used in the transport of the detached particles away from the site of drop impact. One commonly reported transport mechanism is raindrop splash. Raindrop splash moves detached soil particles radially away from the site of detachment. The raindrop detachment - splash transport (RD-ST) system often operates at the onset of a storm when little or no surface water flow occurs. However, splash transport (ST) is a highly inefficient transport system. If the soil has no slope, material splashed away from the point of impact of one drop is replaced by material splashed by other drops in the surrounding area. If the soil surface has a slope, then material splashed downslope travels further than material splashed upslope resulting in the net downslope migration of detached material. That downslope migration increases as the slope gradient increases but it takes many drop impacts to cause much material to move down slope in most cases. Rainfall erosion is either limited by the detachment or transport capacities associated with raindrop impact or surface water flow. RD-ST is a transport limiting process .

2. Raindrop Detachment with transport by Raindrops interacting with Flow
When water flows develop on the soil surface, raindrops penetrate through the flow to detach soil particles which may then be splashed as a result of the breakup of the drop or alternatively may be lifted into the flow where they move downstream as they fall back to the surface. Subsequent drop impacts lift the particles into the flow again and again and they move downstream on each occasion. The resulting transport process involves both raindrop impact and flowing water and, because of this, has been called Raindrop - Induced Flow Transport (RIFT) (Kinnell, 1990). With coarse material, raindrop impact in flowing water may stimulate particles to roll rather than saltate. Consequently RIFT comprises of Raindrop-Induced Saltation (RIS) and Raindrop-Induced Rolling (RIR). RIFT provides more efficient transport than ST. RD-RIFT plays a major role in moving soil material from interrill areas to rills. Splash can also move material from areas not covered by flow to areas where RIFT operates to give RD-ST-RIFT systems. While RIFT is more efficient than ST, it still requires numerous drop impacts to move material downstream and RD-RIFT systems are transport limiting .

3. Raindrop detachment with transport by unassisted Flow
Flowing water moves fine material suspended in the flow by raindrop impacts. In many cases, thin surface water flows have a capacity to cause loose material sitting on the surface to roll or saltate but may not have the capacity to detach material from the underlying surface. However, raindrops penetrating the flow may be able to do this. As a result, particles detached by drop impacts are transported downstream without the need for raindrops to be involved in the transport process. This raindrop detachment – unassisted flow transport (RD-FT) detachment-transport system is more efficient than RD-RIFT. Often, both RD-RIFT and RD-FT occur simultaneously in the same flows, coarse material being transported by RIFT, fine by FT.

The figure below provides a schematic representation of how the detachment and transport forms vary with raindrop energy (e) and stream power (omega) when raindrop energy and stream power are used as measures of erosive forces associated with impacting raindrops and flowing water respectively. In the figure, the critical energy required for raindrops to detach soil particles held in the soil surface by cohesion and inter-particle friction is designated e_c. Raindrop detachment (RD) does not occur unless e is greater than e_c. Interrill erosion and sheet erosion occur in areas where RD occurs.

4. Flow detachment with transport by Flow.
The critical stream power for flow to detach soil particles held in the soil surface by cohesion and inter-particle friction is designated omega_c(bound). Flow detachment (FD) does not occur unless omega is greater than omega_c(bound). Stream power is a hydraulic parameter that varies with flow discharge and slope gradient. Other parameters such as flow shear stress could have been used but the choice of parameter is academic. Consideration of a critical condition for FD remains the same irrespective of what parameter is used. Rill erosion occurs where FD occurs.