Balrothery (Firhouse) Weir
Balrothery Weir, also known as Firhouse Weir, City Weir or City Watercourse, is a significant historical engineering work (HEW) and protected structure in Dublin, hidden within Dodder Valley Park near the M50 at exit 11. Built by the monks of St. Thomas’ Abbey before 1244, this weir played a crucial role in supplying water to Dublin City by diverting the Dodder River to supplement the Poddle River. The Dodder-Poddle water system was essential for the city’s water supply, operated for over 500 years.
Before the construction of Balrothery Weir, Dublin’s water was solely sourced from the Poddle River, originating in the Greenhills area of Tallaght. However, as Dublin grew, this supply became insufficient. The solution was to divert water from the Dodder River at Balrothery, supplementing the Poddle’s flow and ensuring a reliable water supply for the city. This system was so vital that a 1719 Act of Parliament emphasized its importance, noting that without it, both the city’s inhabitants and Dublin Castle would suffer greatly.
The weir’s origins trace back to the monks of St. Thomas’ Abbey, who initially constructed it to support their water needs. In 1244, Dublin’s citizens altered the weir to increase water flow, solidifying its role in the city’s infrastructure. The diverted water passed beneath Tallaght Road, through Templeogue House grounds, and eventually joined the Tymon River, forming the Poddle River proper. This medieval watercourse system remained in use for centuries, reflecting the ingenuity and importance of water management in Dublin’s history.
Over the years, Balrothery Weir has been known by various names, reflecting its significance to different communities. Firhouse residents often refer to it as Firhouse Weir, while those from Tallaght might call it Balrothery Weir. This naming debate culminated in a 2021 motion at South Dublin County Council, where a proposal to officially rename the weir as Firhouse Weir was voted down, leaving it listed as “City Watercourse, Firhouse” in the Record of Protected Structures.
The weir also has a rich engineering history. In 1845, the Dodder was straightened and deepened, making the weir crossing dangerous. A wooden footbridge was built but was soon washed away, replaced by an iron lattice bridge around 1860. Today, the current bridge, erected in 1995 by South Dublin County Council, provides safe pedestrian access across the river. Visitors can also explore nearby Tymon Park via the M50 underpass, making the area a popular destination for both history enthusiasts and nature lovers.
Association with Poddle
The Balrothery Weir diverted water from the Dodder to the Poddle via a man made waterway called the City Watercourse which provided enough water to provide drinking water to a large proportion of the population of Dublin.