<p>Authors use the channel wall loading method to assess the structural stiffness of reinforced concrete open channels used for agricultural irrigation. Our previous studies have focused on verifying the accuracy of this method in laboratory experiments on secondary concrete products. In the present study, we focus on verifying the load–deflection characteristics obtained by this method for several in situ cast-in-place open channels operating in different service environments. Measurement reproducibility accuracy of the load–deflection relationship is also evaluated for three test sets taken at the same location after reinstallation of the equipment, it is found that the linearity of load–deflection relationship was different by the first, second, and third loading cycles in one set, and this tendency was observed in open channels with various cross sections and dimensions. This suggests that the same load–deflection relationship can be obtained regardless of the cross-sectional shape and dimensions, so long as the open channel possesses the applicability of the channel wall loading method and sufficient soundness. The reproducibility of the measurements after reinstallation of this equipment was confirmed to be very high with no significant differences among the three sets. Thus, this method is suitable for performing periodic inspections for aging evaluations.</p>