Ostravice drainage tunnel and Šance waterworks

The construction of the drainage tunnel was one of the primary measures to ensure the operational reliability of the Šance waterworks. Specifically, the project served to divert groundwater that ran down a neighbouring mountain slope and into the raised dam of the waterworks. This process had the potential to damage the reservoir’s sealed core.

When it was first established in 1968, the Šance waterworks facility was the tallest raised dam structure in the country with a height of around 65m. Today, it is the main source of drinking and utility water for the industrial areas of the cities of Ostrava and Karviná. It serves to prevent flooding and also regulates the water level of the Ostravice River below the reservoir.

The excavation of the tunnel, which was nominated Construction of the Year 2014 by the Czech Chamber of Chartered Engineers and Technicians, was executed under very difficult hydro-geological conditions below the groundwater level. A 50m-long section of the drainage tunnel was excavated through unstable hillside scree, while blasting was required to bore the rest of the length through rock areas.

Modern construction materials, such as significant quantities of fibreglass reinforcement and anchor elements, were used to replace classic steel grating and bolts. Access structures and elevated constructions were also made from composite materials. These long-lasting materials will ensure the sustained stability of the tunnel, which is constantly exposed to the effects of groundwater.