After the war it became obvious to the Water Commissioners that it would be necessary to utilise the full yield of raw water available from the Silent Valley and Annalong Valley catchments. Therefore, in place of the impounding reservoir originally planned for the Annalong Valley, it was decided that a new storage reservoir be constructed in the Upper Silent Valley. The contract was awarded to Charles Brand and Son Ltd and work commenced on site in 1953.
Unlike the Silent Valley earth dam, Ben Crom was built as a mass gravity dam – constructed in concrete and dependent on its own weight for stability. It was faced with precast concrete blocks with a hearting of mass concrete containing ‘plumbs’ of granite, some of which were over five tonnes in weight. The cut-off trench below the dam was excavated to a maximum depth of 30 feet to tie in with the solid rock. Much smaller than Silent Valley, Ben Crom is 700 feet long at the top and has a capacity of 1,700 million litres.
As part of the accommodation works a new road was constructed from Silent Valley to the site of Ben Crom Reservoir. Granite stones, which had been excavated from the tunnel leading to the Annalong Valley were used to form the road base.
186 men were employed on the construction of Ben Crom Reservoir, with work completed in 1957.