Grane Valley, Rossendale
The sites, which are the lower two in a cascade of three impounding reservoirs, are “Pennine” type dams with clay cores and are designated as high risk Category A. The Holden Wood embankment was constructed in 1841 and was 100m long and 18m high.
The Ogden embankment was 400m long and 15m high with a crest width of 4.5m, and is the most modern of the three reservoirs in Grane Valley, constructed between 1905 and 1910. Work at Ogden Reservoir included temporary and permanent diversion of pipelines and associated services, the construction of a new spillway formed from 1,300 individual pre cast wedge blocks, weighing 1.3 Tonnes each, the largest spillway of its kind in the UK, new overflow weir and crest bridge, CFA piled foundations, reinforced concrete stilling basin and erosion protection works.
Other works included the demolition and infilling of existing redundant tunnel sections at the toe of the embankment, new RC spillways and lining of existing spillways, vehicular access bridges and landscaping.
Work at Holden Wood Reservoir included the construction of a new spillway complete with new weir and crest bridge, embankment slackening and new filtration systems, replacement of existing scour pipes and upgrading of associated facilities, re-use/remediation of all materials arising from site andremoval of Japanese Knotweed.
Works had to be carefully planned and agreed with the All Reservoirs Panel Engineer.
Key activities and critical temporary works included; cantilever sheet piled excavations, temporary flow diversion channels, propped excavations up to 20m in width, temporary king post retaining systems socketed into rock, temporary service diversions, temporary access bridges over spillways, temporary syphons and over-pumping facilities, temporary bunds to protect breaches in the embankment crest and large crane pads to support attendant crawler cranes amongst others.
All of these works undertaken during harsh weather conditions and within the strict timescales imposed by United Utilities.
The project attracted a visit from the British Dam Society, with a group of almost 40 people visiting in March 2013. Completion of the works within the strict timescales set by UU in order to avoid any disruption to the planned Haweswater Aqueduct outage.