Llyn Brianne

 Although described as ’rockfill’, the triangular section dam actually has a clay core supported by rockfill built with facings at a gradient of 1:1.4. Originally built up from its base at 190 m (600 feet AMSL) to a height of 91 m (297 feet), the crest was later raised  by 1 metre. The crest is 290 m (950 feet) long. The volume of the clay core is 395,000 m³ with 1.69 million m³ of supporting rock fill.