A stone-built weir, constructed to hold back floodwaters at the head of a watercourse near the gravel pits, was the pivot point of a system that deliberately pulled water away from the Dodder and sent it in a different direction entirely. That kind of deliberate manipulation of a river's course is easy to overlook when the infrastructure has vanished, but it points to a surprisingly sophisticated understanding of water management in the Dublin hinterland.

The weir sat at the head of the watercourse at Balrothery, and its purpose was twofold: flood resistance and diversion. From that stone structure, an artificial channel was cut eastward, carrying water from the Dodder to join the river Poddle. The Poddle, now largely culverted beneath south Dublin, was historically one of the city's most important water sources, feeding mills and supplying the medieval city. Connecting the Dodder to the Poddle via an engineered channel suggests a calculated attempt to augment or regulate that supply, though the precise date of the weir's construction is not recorded. According to research by Keeley, the structure was eventually removed during road construction, leaving no visible trace above ground.

There is nothing to see at the site today in the conventional sense. The road that replaced it has done its work thoroughly. What makes the location worth knowing about is less a matter of what remains and more a matter of what the landscape once did. Anyone familiar with the Templeogue area, walking the Dodder bank or passing through Balrothery, is crossing ground that was once actively reshaped by whoever managed water rights and mill supply in this part of County Dublin. The gravel pits mentioned in the historical record are themselves a reminder that this was a working, industrial stretch of river, not a pastoral one. The absence of the weir is, in its own way, informative.