While the British had a sandbagged second line of defence, their front line at the canal was The Bluff. From here, they looked down on the German garrison troops of Alsace, IR99. In response, the Alsatians built themselves some impressive battlements up the side of the canal and onto the plateau above.
The German front line position on the ridge top was a poor piece of low lying ground, cursed with a stream of water that was heading for the canal. Their engineers diverted the water into a culvert and behind the sand sack wall.
It was here that the German mine shaft, the instrument of almost all of the Bluff craters, began its course, striking out horizontally in the direction of The Bluff from a point in the canal bank about 12 metres below the level of the land as shown in the above photograph.
After the war, the stream resumed its course and in July 2005, caused a major collapse in the bank of the canal where it had undermined the sandy soil. A large new ravine sliced through the bank up which the German sandsack fortification had run. The collapse is on the line of, or slightly behind the path of the front line wall. A rough estimate can be made from the position of the still extant remains of the local commander’s headquarters, which is about 6 metres away from the collapse.