The terms in the wave-averaged depth-integrated alongshore momentum balance are populated with detailed measurements from a laboratory basin experiment. Obliquely incident irregular waves were generated in a large wave basin equipped with instruments to collect free surface elevation and velocity measurements over a sand beach. Pumps matched the wave-generated currents, and experimental evidence indicates that the equations can justifiably be simplified by assuming alongshore uniformity. While the use of data measured below the trough level is straightforward, the velocity field in the region near the surface is extrapolated from the measured positions and constrained by conservation of cross-shore mass flux. The role of the dispersive mixing mechanism due to depth-dependent currents is shown to be small but acts to shift the peak of the longshore velocity shoreward slightly. Radiation stresses are the primary forcing mechanism, and computed stresses based on measured wave-induced hydrodynamics are considerably smaller than the widely used linear representation, indicating that the small-amplitude assumption of linear theory is not appropriate in the surf zone. The time-averaged bottom shear stress remains as the primary balance to the gradient in alongshore momentum, and the inferred shear stress compares favorably with the values computed using the quadratic drag law and a spatially constant friction coefficient.