The existing asphalt lining of the upper reservoir, installed 40 years ago, was showing signs of ageing in the slopes facing the sun while the upper part of the slope was vulnerable to the stresses of the constantly changing water level.

The sides of the reservoir have a slope inclination of 1:1.6, creating a very challenging working environment. This is WALO’s particular area of expertise as the company has specialist machinery and equipment developed specifically to operate on very steep slopes. The Dense Asphaltic Concrete (DAC) mix that WALO used for lining the slopes for this project is also specially designed for use on very steep inclines such as these, being quick to lay, very strong, flexible and stable.

WALO milled off 40mm from the upper part of the slope and replaced it with a new DAC layer, which benefited from the addition of polymer-modified bitumen. The other parts of the slope were treated locally and reinstated as required. In total, only 40% of the slope surface needed rehabilitation measures after 40 years of use. Finally the complete slope was sealed by a sand-mastic coat. The base was resealed by both sediments contained in bunded areas and in part new conventional mastic coat. In addition, the joint construction to the bottom outlet and around the outlet tower, were also replaced.