Characterisation of turbulence over an adverse bed slope through the lens of anisotropy, intermittency, chaos and information theoretic diagnostics

Adverse bed-slope transitions can strongly reorganise open-channel turbulence, but their impact on anisotropy, intermittency, and nonlinear dynamics is not yet well quantified. This study experimentally investigates turbulence over an adverse sloping bed in an open channel, aiming to elucidate how bed-induced geometric transitions shape turbulence characteristics. High-frequency three-dimensional velocity measurements were acquired at multiple streamwise stations and depths, and analysed using Reynolds-stress anisotropy diagnostics, intermittency indicators based on quadrant joint-PDFs, velocity spectra, and chaos-information theoretic measures. The results show that turbulence anisotropy evolves gradually along the bed transition. The flow shifts from predominantly bi-directional states upstream toward more mixed states over the slope, followed by partial recovery downstream. Anisotropy is strongest near the bed, exhibits peaks just below mid-depth, and becomes more vertically self-similar with increasing current magnitude. Positionally, no anomalous tendency is observed under stronger currents. In contrast, intermittency remains strongly localised, with slope-transition stations acting as hotspots where joint-PDF contours broaden toward ejection-sweep dominance and spectra steepen. This is consistent with sporadic bursting and sharper departures from local trends, whereas non-transitional stations retain tighter contours and flatter spectra indicative of steadier coherence. Chaos and information analyses further indicate increasing trajectory divergence and reduced memory with height as slope-driven upwellings are present. Collectively, these observations suggest that anisotropy trends and intermittency hotspots can exhibit distinct spatial signatures. Therefore, anisotropy should be interpreted alongside intermittency and memory metrics for position-aware turbulence assessment over adverse slopes.