A trench had been dug across the apron during the installation of aerodrome lighting. It had been back filled with earth. Whether the compacting was inadequate or whether the rain had been exceptionally heavy is not known, but heavy rain had made the earth fill very soft. The pilot landed just after a very heavy rain shower had passed through the area. There was about 2 cm of water covering the ground which made it near impossible to see the trench. When the aircraft's nosewheel entered the soft earth the aircraft veered sharply to the left and travelled about two metres before the nose gear hit a concrete pad and collapsed. Because the trench was almost impossible to see from the cockpit of the aircraft it is considered that it was a hidden hazard. The trench had not been marked by unserviceability cones. This accident was not the subject of an on-site investigation.