Rehabilitation of Canals with Watertight Geomembranes, in the Dry and Underwater

Geomembranes are watertight synthetic materials, factory-manufactured under computer-controlled procedures that guarantee constant properties and quality, and supplied as flexible sheets a few millimetres thick. Geomembranes have been used to waterproof all types of hydraulic structures since more than half a century. In canals, their use started after World War II. They have been adopted to restore watertightness of deteriorated concrete or bituminous concrete linings, and to repair failing joints. Besides this waterproofing function, exposed geomembrane systems provide the additional function of increasing the water flow. All types of canals have been lined, be it hydropower canals with high water velocity, or large irrigation canals with varying sections, or small flumes and aqueducts. The paper discusses, through some significant case histories, the design options for the various projects, addressing the anchorage and drainage systems, taking into account the dynamic action of water flowing inside the canal, of water acting behind the geomembrane because present in the slopes, and the generally worst-case scenario of water infiltrated via accidental damage under the geomembrane; the influence of the drainage system and of the type of geomembrane on the anchorage will also be addressed. The paper finally introduces a totally innovative technology, SIBELONMAT^®, which allows repairing canals underwater, without impacting on the operation, if needed with un-manned procedures, using ROVs. This new technology, which uses panels of a double geomembrane mattress filled with mortar, and joined with a watertight device, has already been successfully installed underwater in two pilot projects in two water supply canals, with no reduction of water speed. The technology can be considered also for new construction of canals and of embankment dams.