An Act of Parliament in 1910 allowed for the creation of the Abertillery and District Water Board and the construction of the Grwyne Fawr reservoir, NPRN 267350. The reservoir was needed to supply fresh water to the growing settlements in Monmouthshire. The construction of the reservoir began in 1912 after William Underwood won the tender to undertake the work. By 1915 he had constructed a small temporary reservoir to the north of the modern reservoir and piped the water down the valley to fill service reservoirs. The road, NPRN 267109 had been constructed along the northeast side of the valley and railway NPRN 267326 along the valley floor. The war years brought work to a standstill, but by 1919 the construction site of the new reservoir was back in business. The building of the reservoir was finally completed in 1928, after which the railway and mechanical structures used to build it were rapidly dismantled and removed.
Source: Tipper Rev DA, 1975, Stone and Steam in the Black Mountains
During Upland Survey work in 2007 many features connected with this construction phase of the reservoir were recorded and they have been brought together under this NPRN.
J.J.Hall, Trysor, 15 February 2008