On the multifractal and intermittent characteristics of tidal flows

We investigated the distinct directional variations of multifractal and intermittent characteristics of ebb and flood flow velocities at the Nodule Point, WA, tidal energy site, with complementary analysis at the East River, NY. To assess multifractality and intermittency, we compared scaling exponents of the structure function, distribution flatness, detrending moving average (DMA) analysis, multifractal detrended fluctuation analysis (MF-DFA), and high-order spectral moments. Our

findings indicate that tidal flows exhibit higher long-range dependence (LRD) and intermittent levels during ebb flow sections. Conversely, flood flow sections show increased multifractality and greater sensitivity to higher turbulent fluctuations. Through DMA and MF-DFA, we identified multiple fractal scalings within the tidal flow data, evidencing the complex multifractal nature of these flows. Scale-dependent intermittency levels, examined using spectral kurtosis, reveal a distinct pattern in tidal flow intermittency. This pattern contrasts with the monotonically increasing intermittency observed in wall-bounded and grid turbulence and displays a Gaussian-like PDF distribution for small-scale events at both tidal sites.