The recent drought in Ireland has ended with heavy rain showers affecting most parts of the country today. And after heavy rain there is one historic piece of engineering that is worth a visit. It is the noisy and impressive Balrothery Weir on the River Dodder. It is located adjacent to the Tallaght/ Templeogue junction on the M50, junction 11. The weir is 75 metres long and 5 metres high.

A weir was first constructed at this location 800 years ago. At that time and for hundreds of years afterwards the main water supply for Dublin City was the small Poddle River. Water from the River Liffey wasn’t used as the river was tidal, and therefore salty, where the city first developed.

But the flow of the Poddle River was small, especially during dry weather. Soon it was insufficient to meet the needs of the growing city. To boost the flow of the Poddle, in the 13^th century a stone weir, Balrothery Weir, was built across the adjacent River Dodder and a 3 km feeder canal was constructed from it to the River Poddle. Sluices were used to divert water from the weir, down the canal to the Poddle, and hence to the citizens of the city.

The weir itself is always worth a visit, but it is particularly spectacular when the Dodder is swollen after heavy rain. The sluices and part of the original feeder channel are still visible but its been a long time since it was used for its original purpose as Dublin now has alternative water sources. Local residents are proud of this piece of historic engineering and during my last visit a well attended clean-up was taking place. See photographs of the weir below, click to enlarge.