Correlations on weakly time-dependent transcritical white-hole flows

We report observations made on a run of transcritical flows over an obstacle in narrow channel. Downstream from the obstacle, decelerate supercritical to subcritical, typically with undulation subcritical side (known hydrodynamics as undular hydraulic jump). In Analogue Gravity context, this transition corresponds white-hole horizon. Free-surface deformations are analyzed, mainly via two-point correlation function which shows presence checkerboard pattern vicinity undulation. nongated where horizon occurs far downstream is shown be due low-frequency fluctuations associated slow longitudinal movement It can thus considered artifact time-varying background. gated flows, however, ``attached'' and its strongly suppressed. case, observed likely stochastic ensemble surface waves, scattering background that essentially stationary.