A method for laying down and tensioning a waterproofing liner on a surface of a hydraulic work, such as, for example, a canal, a dam, a water basin, or a hydraulic tunnel, wherein the waterproofing liner is fastened, tensioned and made to sealingly adhere to the surface of the hydraulic work by sealingly clamping the waterproofing liner by a plurality of locking assemblies, wherein each locking assembly comprises a lower metal section bar anchored to the surface of the hydraulic work, and an upper metal section bar that conforms to the lower section bar; and wherein the waterproofing liner is sealingly clamped between the lower section bar and the upper section bar; said method being characterised by the steps of a) configuring each lower section bar, or an additional elongated anchor element, with a set of anchor holes at a plurality of anchoring zones, in axially spaced apart positions; b) marking anchoring zones on the surface of the hydraulic work with a set of reference marks in positions corresponding to the positions of the anchor holes of the anchoring zones of the lower section bar, or additional anchor element; c) perforating the surface of the hydraulic work at at least one reference mark of the anchoring zones of the surface of the hydraulic work; d) positioning each lower section bar, or additional elongated anchoring element, aligning the set of the anchor holes of each anchoring zone of the section bar with the perforations made at each anchoring zone of the surface of the hydraulic work; e) anchoring the lower section bar, or the additional elongated anchor element, to the hydraulic work, by anchoring devices passing through said anchor holes aligned to the perforations made at the reference marks; and f) laying down, anchoring and tensioning the waterproofing liner, connecting the upper section bar to the lower section bar of each locking assembly, sealingly clamping the waterproofing liner between opposite slanted flat walls (13; 14) of the lower section bar and the upper section bar. a) configuring each lower section bar, or an additional elongated anchor element, with a set of anchor holes at a plurality of anchoring zones, in axially spaced apart positions; b) marking anchoring zones on the surface of the hydraulic work with a set of reference marks in positions corresponding to the positions of the anchor holes of the anchoring zones of the lower section bar, or additional anchor element; c) perforating the surface of the hydraulic work at at least one reference mark of the anchoring zones of the surface of the hydraulic work; d) positioning each lower section bar, or additional elongated anchoring element, aligning the set of the anchor holes of each anchoring zone of the section bar with the perforations made at each anchoring zone of the surface of the hydraulic work; e) anchoring the lower section bar, or the additional elongated anchor element, to the hydraulic work, by anchoring devices passing through said anchor holes aligned to the perforations made at the reference marks; and f) laying down, anchoring and tensioning the waterproofing liner, connecting the upper section bar to the lower section bar of each locking assembly, sealingly clamping the waterproofing liner between opposite slanted flat walls (13; 14) of the lower section bar and the upper section bar.