Compared to the actual recorded HWR distance across the 20 transects from 2017 to 2018, the RMSE was 6.5 m for MAC, 4.2 m for EXT, 3.3 m for OBS and 2.7 m for MI. The mean absolute errors were 5.3 m, 3.4 m, 2.3 m and 1.8 m, respectively. For MAC only one transect was within 1 m of the actual headwall position in 2018, while eight had errors over 5 m. The same statistics for EXT were five under 1 m and five over 5 m, for OBS there were nine under 1 m and three over 5 m and for MI there were nine under 1 m and one over 5 m.