Multidisciplinary Projects

Remediation of the tidal river Ría Avilés (Spain)

In the middle of last century, the city of Avilés developed to become the leading centre of the iron and steel industry of Asturias. The river was even used as a sedimentation basin for the coke works, thus leaving behind a miserable industrial legacy of sediments contaminated with PAH's and heavy metals. In addition, the river bed became dry at low tide with contaminated sediments being exposed to the open air.

In total, some 140,000 cubic metres of contaminated sediment over a length of 1.9 km were dredged. In the central canal, the river was made narrowed 50 to 30m. In the low-lying portions of the river, where tidal movements vary from 0 to 4.5m, a cable crane dredged the sediment from the bank. Further upstream, two new small dykes were constructed for flood protection.

All excavated material was brought to a nearby disposal site for inert waste that was already used by the steel plant. A new disposal site of 3 hectares was created with an impermeable bentonite base, impermeable HDPE capping, a layer of gravel and drainage tubes. One hectare was used as a lagoon field for the dewatering of sediment. The 'dry' sediment was then stabilised and immobilised and ultimately buried in the disposal site.

The complete remediation operation took more than twenty months. After all sediment was removed in October 2004, the banks of the river were again installed with a few other upgrading works such as the construction of parks, bridges and walking zones. Two water containment structures will continuously keep the river at a low water level and regulate the future water supply.