Waun Pond—New Overflow

Following a periodical inspection of Waun Pond, Blaenau Gwent County Borough Council appointed Fairhurst to address safety recommendations. The overflow capacity was found to be grossly inadequate. The solution involved design of a new overflow which accounted for significant physical constraints including services laid along the crest of the dam below a public road and conflicting stakeholder interests in terms of amenity and flood risk downstream.

The adopted solution was a box-type overflow, with the potential for flow to enter on all four sides, discharging through culverts formed by tunnelling below the crest of the dam using pipe jacking, into a downstream stilling basin and channel. The paper covers the flood study, design and construction aspects of the new overflow.