Talla Reservoir is 120 years old!

“The typical gradient of the aqueduct is 1/4000, therefore for every 1m of drop you travel 4Km of distance”

David J. Rankin
Scottish Water Senior Engineer

A RESERVOIR that serves Scotland’s capital city has recently marked its 120^th year in service.

Talla Reservoir, situated near Biggar, South Lanarkshire, is one of Scottish Water’s longest serving reservoirs, ensuring Edinburgh has fresh and great tasting water.

The mammoth body of water, completed in 1905 has a wealth of history dating back to the Victorian era and marvels some incredible masonry and engineering brilliance.

Back then, Edinburgh was expanding and the population was growing at an extreme pace, forcing government officials to look at other ways to provide locals with water.

In 1895 the decision was made to start construction of Talla Reservoir, overseen by the newly formed Edinburgh District and Water Trust.

The project would see a new reservoir built in the Talla Valley, near Tweedsmuir with 35 miles of aqueduct to feed the water treatment works of Fairmilehead & Alnwickhill.  The aqueduct now supplies water to the Glencorse Water Treatment works in Penicuik. Completed in 2012, the state-of-the-art works pioneered new technology and ensure that the Edinburgh had wholesome water for generations to come.

The reservoir would outsize other nearby reservoirs at Gladhouse, Portmore, Roseberry and Edgelaw combined – holding approximately 2.8 billion gallons of water or 12.7 billion litres, the equivalent of 5092 Olympic sized swimming pools.

Engineers at the time, had the difficult task of building a reservoir in this remote location. This led to the construction of a dedicated railway from Broughton to the construction site in the Talla Valley, – transporting equipment, materials and workers, the majority of whom were Irish navvies, to the site.

While the construction of the reservoir and aqueducts took place, engineers would climb to vantage points with strategically placed observation towers and use a brass surveying telescope to check the line and level of the aqueduct, and siphons being built. 

One of these surveying telescopes was discovered by the Lothian Regional Council back in 1988 and donated to The Institution of Civil Engineers (ICE) Scottish Museum, at Heriot Watt University where it is still proudly displayed. Scottish Water’s Senior Engineer, David J. Rankin is a member of the Institution, and a volunteer with its Panel for Historical Engineering Works (PHEW).

He said: “It is quite incredible that the telescope has survived to this day, The surveying telescope, technically known as a transit instrument, was a significant part of the construction of the aqueduct and a tangible connection to the engineers who built the scheme.

“The engineers of the time would have used this instrument to make certain that the gravity fed aqueduct had a sufficient fall to allow the water to flow all the way to Edinburgh.

“The typical gradient of the aqueduct is 1/4000, therefore for every 1m of drop you travel 4Km of distance.”

He continued: “It would have been critical for the engineers to ensure gradient was maintained so that water would make it the 35 miles to the city. Even using modern equipment, such as satellites and GPS working to an equivalent tolerance would be very challenging.”

The entire project cost approximately £1.96 million which in today’s money would amount to around £208.6 million.

Nowadays, the reservoir is managed by Principal Engineer, Dougie Scott who has amassed a 40+ years’ experience in the water industry.

Dougie is the appointed Supervising Engineer for the Talla Reservoir, and is responsible for ensuring that the dam, is regularly inspected and maintained to the highest standards of safety. As part of his duties, he is required to check the operation of the original Victorian gun metal valves, which keep the city in supply. 

Incredibly, he’s been in charge of Talla’s operation for around a fifth of its life span.

He said: “It really is quite different to many of the other reservoirs in my reservoir portfolio, with the intricacies and processes needed to operate all the different mechanisms.

“I’d say it’s my favourite, from the masonry and stonework to just the operation in general.

“It’s amazing to think that in years gone by, to simply open one valve here, it would’ve taken eight hours and a three-person team, it shows you how much more advanced we have become.”