The City Weir
Firhouse Weir, also known as City Weir or City Watercourse is probably the best known landmark in Firhouse and was once of great importance to every citizen of Dublin. Prior to 1244, the water supply for Dublin City was provided by the Poddle, which rises in the Greenhills area of Tallaght but this water supply was inadequate for a growing city in the early thirteenth century. It was decided to convey water from the Dodder in order to supplement the supply from the Poddle, and it was here at Firhouse Weir that the Dodder was diverted.
It was thought that the city’s citizens had built the weir in 1244 but recent research has shown that it was built by the monks of St. Thomas’ Abbey on Thomas Street at an earlier date, and then altered by the citizens in 1244 to increase the flow of water. Almost all of the Dodder’s water was diverted into the weir, through an open aquaduct which then directed the water into a man-made channel or watercourse which flowed beneath the main Tallaght road and Wellington Land and skirted the wall of the old Templeogue graveyard. It then headed for Templeogue House, beyond which it joined the Tymon River coming from Tallaght North. This confluence then became the Poddle River proper. The Dodder-Poddle water system was completed about the middle of the thirteenth century and remained in operation for five hundred years.
The importance of the river as a source of water to the citizens of Dublin can be gauged from an incident in 1738. Sir Compton Domville, then resident at Templeogue House, was able to have his nephew Lord Santry, a member of the Hell Fire Club, saved from execution for the murder of one of his servants by threatening to block off the watercourse which flowed through his lands. The threat was successful as the citizens had no other supply.
A 1719 Act of Parliament refers to the watercourse as “the chief supply of water not only for the inhabitants of the said city; but also for this majesties Castle of Dublin, and without which it would suffer exceeding great prejudice.” The act sought to make provision for the cleaning and repairing of the watercourse because “…tuck mills, in which urine, soap and other unwolsome materials are made use of, and diers of linnen and woolen cloath and yarn, and skinners dip, wash, scour and cleanse great quantities of died linnen and woolen cloath, yarn and skins in the said water-course, by which the water is greatly corrupted, endangering the healths of the inhabitants of the said city.” It seems there was also a problem with mills building along the watercourse, erecting dams and ponds, and obstructing the flow of water into the city.
From 1845 when the Dodder was straightened and deepened, there was a precipitous drop of 20 feet into the river bed at Firhouse Weir. For many years after this, the only way for pedestrians to cross during a flood was the dangerous one of wading along the top of the weir. A plank bridge that was built was washed away and a lattice bridge was erected about 1860. This bridge was replaced by the present structure when a new bridge was opened by South Dublin County Council in 1995.