The water velocity and associated physical forces affect the distribution of organisms in rivers and streams; changes in the flows can also affect the organic matter decomposition and transport of detritus in lotic systems. The main objective of this study was to evaluate (120 days) the effects from the water flow velocity on the mass loss of leaves and stems in artificial channels (at 24 ± 1.0°C; current velocities: 0, 5, and 10 cm s−1). The kinetic model used suggested that in addition to abrasion, the velocity of flow stressed the detritus fibers altering the decomposition pathways. Overall, the changes in the kinetic parameters varied linearly with the increase in flow velocity. Weight losses of the leaves were more affected by the flow velocity than those of the twigs. However, abrasion was more effective in the twigs than that in the leaves detritus. In the lotic systems, the leaves have greater importance in the detritus chains in the short term and in the conditions of backwater. The boost of flow velocity tends to change the refractory fractions (RPOM) into more labile/soluble compounds and increase the values of RPOM rate constant, owing to abrasion.