The Terroba Dam impounds the winter rainfall to enable constant irrigation of the fertile valley during the drier spring and summer months. The initial plan for the dam included an embankment dam with a clay core. However, clay is in short supply in the surrounding area so sourcing and transporting clay to the site would have proved prohibitively expensive. An alternative technical solution was required and so to solve the problem, the design was changed to a bituminous upstream lining system. As the design had been so radically changed, the earthworks were completed much more quickly so far more economically. Also, by substituting clay with a more sophisticated option of a bituminous lining, the material costs for the project were considerably reduced. WALO, with its specialist Dense Asphaltic Concrete (DAC) capability, was selected to provide the lining system, given that DAC is ideal for projects like this, being highly robust yet flexible and quick to lay, even on very steep slopes.

The work also included a 425m joint construction to the plinth and abutments and 305m joint construction to the parapet wall at the crest. This meant the WALO team had to bond together securely two very different materials – the flexible DAC and the rigid concrete. This kind of highly specialised technical work can only be carried out successfully by exceptionally skilled and experienced craftspeople. The bituminous upstream lining system to the dam constructed by WALO covered a total surface area of 23,100m2, with a steep 94 m long slope with an incline of 1:1.8. The lining system consisted of 150-200 mm of crushed aggregates, 2 kg/m2 of emulsion spray applied tack coat, an Asphaltic Binder Layer (ABL) of 70 mm and a DAC layer of 60 mm and 2 kg/m2 mastic coating.