Geograph - photograph every grid square

The weir is marked on the 25-inch first-edition OS map (surveyed in 1860), and on present-day large-scale mapping. There is a 2- or 3-foot drop at the edge of the weir. This is of necessity a close-up view, since the structure is not visible from further away.

A couple of years later, the clearing of Rhododendrons from the area made a better view possible, namely, NS4277 : Old weir on the Overtoun Burn, which provides more context.

In the area just downstream, other modifications can be seen, although they are not of a kind that would be recorded on the map; they are shown and described in NS4277 : The Overtoun Burn. The short intervening part of the burn, immediately downstream of the weir, is presently shaded by rhododendron bushes, but probably exhibits the same modifications. (However, for some context, see NS4277 : Dry-stone wall; the weir is just beyond the far end of the visible part of the wall.)

Just upstream of the weir, the ground above the western side of the burn is steep, with some overhangs; the steep slope consists of Ballagan Beds, which are fairly crumbly (compare NS4178 : Ballagan Beds in Auchenreoch Glen). It therefore seems likely that the weir was built in order to slow the burn there, reducing erosion and undercutting of that slope: NS4277 : The Overtoun Burn.