Client:
Critical water infrastructure for Manchester
The Nab Scar Aqueduct is a critical component of the Thirlmere–Manchester water supply system, running beneath the flanks of Nab Scar above Rydal Water in the Lake District National Park.
Constructed in the late 19th century, the aqueduct forms part of the gravity‑fed infrastructure that supplies a significant proportion—around 20%—of Manchester’s drinking water. Rather than a traditional visible aqueduct, the Nab Scar section is largely concealed within the hillside, carried through tunnels and conduits beneath unstable rock and scree slopes, making it both geotechnically complex and strategically important to regional water resilience.
The location of the aqueduct beneath steep, fractured ground has long presented stability challenges, particularly where natural slope movement posed a risk to the integrity of the buried conduit. As a result, Nab Scar has been the focus of careful inspection, maintenance and remedial works to protect the structure and ensure continuity of supply. The aqueduct’s setting within a protected landscape has also meant that any intervention must balance engineering requirements with environmental and visual sensitivity.
A critical structure
In 2009, extensive remedial works started to the aquaduct that necessitated a monitoring system to be installed. A broad range of monitoring techniques implemented by SIXENSE ensured the stability of the structure during the works, preventing any damage to the water main, and determined the success of the operation after works were completed.
To provide surface monitoring characteristics along the scree slope, our CYCLOPS ATS system was used together with a 5 m grid of monitoring prisms.
To determine vertical deformations of the conduit, horizontal In-Place Inclinometers (IPIs) were installed within the conduit. Vertical deformation of the slope was obtained using IPI strings installed within boreholes drilled directly into the hillside. Induced vibration were considered to be a potential problem during the remedial works, therefore, portable geophones were used around the conduit.
The data acquired from the instrumentation and monitoring installed at Nab Scar Aquaduct was stored and managed using a datalogging solution on site which imported the information into Sixense’s Geoscope software. Geoscope was also accessible to the client, providing them real time access to the data as well as the ability to run fully customisable reports, as required.
CYCLOPS ATS
Horizontal IPI's
Vertical IPI's
VW Strain Gauges
VW Crackmeters
Geophones
