The unlined dam spillways are subjected to significant safety risk from the hydraulic rock mass erosion. The current rock mass erosion assessment methods rely on semi-empirical approaches; however, discrepancies have been observed between the measured and actual erosion depths. Semi-analytical methods based on the Comprehensive Scour Model (CSM) provides a promising solution which requires adaptation for the parallel flow spillways. This study focuses on investigating the effect of joint orientation on the non-dimensional dynamic uplift pressure coefficient for parallel flow spillways using reduced-scale dam spillway model tests. The experimental setup consists of arrangement of nine blocks in a 3 × 3 matrix in different orientations within a metal box, i.e., 45°, 0°, and +45° to the spillway surface, where the central block is instrumented. The hydraulic pressures around the instrumented block are measured under different flow rates and the dynamic uplift pressure coefficients are obtained which are related to the joint orientation. The findings provide valuable insights into mitigating hydraulic erosion risks in dam spillways by understanding block stability under the action of destabilizing hydraulic forces and resistive forces.