Submarine cable behaviour is experimentally studied in order to evaluate on-bottom stability of cables placed on rocky seabed with high roughness and submitted to combined wave and strong current. For that purpose, hydrodynamic loads are measured on a fixed slender cylinder closely fixed to a horizontal plate, with or without large roughness. A specified set of load cases (forced oscillations, current, forced oscillation + current) is considered to assess the hydrodynamic loads acting on the cylinder placed near a wall for varying gap-to-diameter ratios. The roughness effects on cylinder loads and on the flow are studied in detail. The result show a significant difference between rough and smooth bottom configurations. Indeed, the loads measurements and hydrodynamic coefficients are significantly lower with the presence of a rough plate near the cylinder. Especially for drag and oscillatory drag coefficients, however the inertia coefficient presents less differences.