Alongshore fluid motions in the swash zone of a sandy and gravel beach

► Alongshore fluid motions in the swash zone of a sand and gravel beach. ► Cross- and alongshore-directed flows are of the same order of magnitude. ► Alongshore momentum is advected into the swash zone from surf zone. ► Strong alongshore-directed vertical shear occurs during backwash. ► Alongshore Cd is of the same order of magnitude as the cross-shore flows.