Understanding the hydraulic resistance and stability of boulders is essential for river engineering, river morphology, and hydraulic structure design. This study quantifies hydrodynamic forces acting on a cubical block resting on a smooth, rigid bed under near-critical to supercritical flow conditions, with bed slopes of 0.4-−1.3% and Froude numbers ( Fr ) in the range $$1.2 \le Fr \le 2.8$$ . Time-resolved force measurements...