# Experimental Study on the Near-Red Flow Characteristics of Alluvial Channel with Seepage
## 3 Results and Discussion
However, the positive value of \(S(u)\) at near-bed flow is (slightly) higher in the case of downward seepage, signifying the increasing trends of the streamwise flux of Reynolds normal stress, which increases turbulence in the seepage bed. The influence of the downward seepage also increases the magnitude of the negative values of \(S(w)\) within the near-boundary zone. This would indicate the surge in vertical flux of the vertical Reynolds normal stress. The skewness likewise highlights the real characteristics of the bursting events [28], which can significantly change the existing  
Figure 6: (**a**) Instantaneous RSS data trend at \(z=0.05\)\(h\) and (**b**) vertical profiles of RSS for all experiments in this study. hydrodynamic conditions. In this regard, [PERSON] [29] discussed the effects of turbulent events on the initiation of salting grain movement at the near-bed, and observed that the sweeps and outward interactions had a key influence on the particle's entrainment. As already remarked above, it is clear from Figure 8 that \(S(u)\) and \(S(w)\) are, respectively, positive and negative in the vicinity of the bed surface, suggesting the dominance of sweep events in this region. Away from the bed, the governance of ejection events causes \(S(u)\) to be negative and \(S(w)\) to be positive for the rest of the flow depth. Hence, the current results would provide an indication that a streamwise acceleration is linked with a downward flux producing sweep events, whereas a streamwise acceleration is linked with a flux in the upstream direction causing ejection events. The fourth-order correlation, termed kurtosis, characterizes the intermittency of turbulence. The variations in the kurtosis [\(K(u)=\overline{u^{\prime 4}}/\sigma(u)^{4}\), \(K(w)=\overline{w^{\prime 4}}/\sigma(w)^{4}\)] for no seepage and in the presence of downward seepage are presented in Figure 9 with respect to \(z/h\), where \(K(u)\) and \(K(w)\) indicate the kurtosis in the streamwise and vertical direction, respectively. The magnitude of \(K(u)\) and \(K(w)\) should be three in the case of isotropic turbulence with Gaussian distribution. However, on the basis of normal distribution, [PERSON] [30] and [PERSON] [31] suggested that the magnitude of \(K(u)\) should be 2.86 and 2.85, respectively. Figure 9 shows that the values of the kurtosis \(K(u)\) are incl  
Figure 8: Profiles of skewness (**a**) \(S(u)\) and (**b**) \(S(w)\) for all experiments in this study. Figure 7: Profiles of (**a**) streamwise turbulence intensity and (**b**) vertical turbulence intensity for all experiments of this study. \(z/h=0.2\)-0.3, in the main flow region. Therefore, the obtained values indicate a certain deviation from the normal distribution and a higher level of turbulence intermittency was observed in the main flow region, which confirmed that sweep and ejection are the responsible bursting events that play a strong intermittent role in turbulence production. These results appear consistent with those of [PERSON] et al. (2018) and [PERSON] et al. (2018) in their modeling of saltating particles' diffusion in turbulent water flow; the high values of the skewness and kurtosis reflected high levels of intermittency in the particle trajectories. Remarkably, \(K(u)>3\) implies a profile with a peaky signal pattern of intermittent turbulence events, whereas \(K(u)<3\) would imply a flat pattern. The experimental values of \(K(u)\) lie between 0 and 2.4 in the near-bed flow, which suggests that the signal inclines to yield a flatter pattern for the flow interacting with the bed surface. Within the near-boundary region, the averaged values of \(K(u)\) and \(K(w)\) are larger in the presence of downward seepage than in the case of the no-seepage bed. This indicates that the downward seepage process exacerbates the degree of turbulence intermittency at the near-bed flow.