Whilst St Helen’s Loch was evidently a natural feature, it was enlarged in the early nineteenth century to function as a mill pond or reservoir. The original form of the loch is difficult to determine. Pont’s map is unreliable in detail and even though it shows the loch aligned north/south with a burn issuing from the north end this is far from certain. Grassom’s map of 1817 is more accurate and shows the loch aligned south-west/north-east. Excavations to enlarge the area of this sheet of water and raise an embankment to its west have obscured the natural contours. Logic suggests that the early loch was created by the moraine barrier on the 200ft contour which includes Elf Hill. Here the water ponded up until it was able to top the ridge just to the west of Elf Hill. It then descended through the Antonine Wall and into a west/east valley where it turned to the west and then north-west passing to the east of the Chapel Yard and into the River Bonny.
At the point where it turned to the west another mill pond was created known as Shaw’s Dam (today this area still floods due to the presence of the later railway embankment). This is shown on Horsley’s map of 1732 and Roy’s 1755 map of the Antonine Wall. It would have served the Bonny Mill further downstream. It also appears on Roy’s great map of c1780. These maps show a branch of the Beam Burn turning west before reaching St Helen’s Loch, eventually crossing the Antonine Wall a little to the east of the motte at Seabegs; here it was joined by the Milnquarter Burn. It was this arm which was dammed to create the “Damhead” for the distillery. It then rejoined the eastern branch a little to the south of the former Bonnymuir Brickworks. The “lands of Seabegs called Damhead and Broomhill” are mentioned as early as 1666 (Reid Notes).
St Helen’s loch was extended westward around 1830. This required the removal of a large amount of earth from the ridge there which was redeposited to form an embankment further to the west. A sluice in this embankment released the water into the western branch of the Beam Burn to the distillery. The little valley to the west of Elf Hill was also built up with earth and a stone-lined channel and sluice inserted to act as an overflow. A stone channel through the Antonine Wall must belong to this time. Presumably Shaw’s Dam no longer functioned.
Falkirk Local History Society 