This threshold was set on the basis of failures of reservoirs of this size in the 1920s which caused loss of life and prompted the introduction of a 1930 Act.
Pennwyd y trothwy hwn yn sgil methiannau cronfeydd dŵr o’r maint hwn yn yr 1920au a achosodd farwolaethau ac a ysgogodd Ddeddf 1930.