Sediment transport consists one of the major problems in earth surface dynamics. Obtaining better understanding of the fundamental process and dynamics of grain mobilization is essential to improving our capacity to model and predict such phenomena. Even though recent research has made progress towards linking coherent flow structures with bed material entrainment, there is still a need to appropriately classify them and evaluate their impact accordingly. The objective of this work is to employ modern signal analysis techniques in finding the relevant time and length scales that characterize the near bed turbulent structures that lead to the initiation of motion of coarse bed particles. In addition to probability distributions of various temporal characteristics linked to grain dislodgement, the frequency and relevant scales of the energetic flow structures are found by means of wavelet multilevel decomposition.