The scope of work is to divert the 1200mm main to enable construction works at the A93 Milltimber Junction, a critical intersection on the Aberdeen Western Peripheral Route (AWPR).
There are two water treatment works that deliver fresh water to the inhabitants of Aberdeen. One is located at Mannofield in the city, the other – Invercannie – is 18 miles west of Aberdeen near Banchory. Both works treat water taken from the River Dee. Two acqueducts – one built in 1866 and the second in 1924 – carry the water from Invercannie to Aberdeen. The 1924 pipeline is constructed from 1200mm diameter cast iron pipe: it’s huge!
The works have involved the installation of two under-pressure tees and the construction of a 250m ductile iron bypass or ‘diversion’: the diversion will have to be thoroughly flushed and chlorinated before it can be used to transport potable water. Once this has been achieved, the original pipe section can be cut out allowing works to begin on the junction. The final stage will see W M Donald reinstating the original pipe and running it above the newly constructed underpass.
"I’ve never worked on a live diversion with pipes of that size’" commented Project Manager, Willie Merson. "To ensure we meet the quality standards set by the DWQR (Drinking Water Quality Regulator) we are flushing the diversion several times. Each flush requires 250,000 litres of water which we then divert to a natural SUDS (Sustainable Urban Drainage) basin formed on site. The basin acts as a natural filter and allows the water to return safely to the local environment."
The A93 is a major route into Aberdeen and the project has required much of the work to be undertaken at weekends and at night to minimise disruption.