The effect of interaction between erosion processes has not been studied in detail, so that the existing available literature, which directly addresses the interaction between erosion processes, is very limited. Numerous laboratory experiments have shown that the rate of erosion in a rain-impacted flow is greater than for unimpacted flows of similar depth and velocity. In erosion studies and in modeling the processes involved it is questionable whether it is justifiable to simply add the contribution of each separate erosion processes to give the total sediment concentration, or whether there may be some form of interaction between the two types of erosion process, positive or negative. Current modeling methods only indirectly have implication for the magnitude of such interaction. The experiments reported in this paper were carried out in the 5.8 by 1.0 m Griffith University Tilting Flume Simulated Rainfall (GUTSR) facility, using two different soil types. It was found that sediment concentration due to flow-driven and rainfall-driven erosion processes, or combination of both processes, depends on soil type and slope steepness. It was found that at low slopes rain-impacted flow can erode soil more rapidly than comparable flow without raindrop impact. At steady state or apparent equilibrium conditions there was a positive or synergistic interaction between rainfall and flow-driven erosion for the silty soil with a finer soil size characteristic than the coarser loamy sand, where the interaction was negative.