Nant-y-Gro dam was a small gravity dam built during the construction of the Elan Valley Water Scheme (nprn 96459) between 1893 and 1904 to supply water to the workmen's village below and was abandoned on completion of the Scheme. It was used in 1942 for Dr. Barnes Wallis' secret tests during the development of the 'bouncing bomb' used to attack dams in Germany. The test explosion left the dam with a large break in its centre measuring 19m wide and 8m high; the two remaining ends of the dam wall stand to their full height of 11m.
Source: Cadw scheduling description.
RCAHMW, 04 March 2011.