Had it happened during the week, there would have been even more deaths.
The flood affected all the camps along the river but elsewhere most of the inhabitants were able to get to higher ground.
At Kopuawhara, a bridge was washed away by the force of the water and the men were trapped on an island between the river and a raging channel of water on the other side.
Also marking the occasion were three generations of the descendants of William Charles Robinson, who drowned in the flood at the Bartlett's camp further upstream,
The inscription on the monument made sad reading for supporters of the line.
"They have built and their handiwork remains their sure memorial."
KiwiRail staff sent a wreath and a message.
Representatives of Ngai Tamanuhiri, the majority landowners of the surrounding forests, said they were working with Juken New Zealand, the tramping club and Walking Access New Zealand to provide better access to the site and to restore signage marking it, which was lost after Cyclone Bola.