A method for fastening a waterproofing and protective membrane of elastically flexible and extensible sheet of plastic material onto a surface area (11, 12) to be covered of a hydraulic structure by mechanical fastening devices (14, 15, 16), comprising the steps of: a) providing a plurality of punctual fastening devices (14, 15, 16) each comprising a punctual anchoring portion (18, 23, 32, 40) conformed to penetrate into the hydraulic structure or into the underlying ground, and a membrane fastening portion (22, 23', 35', 40') extending from the anchoring portion (18, 23, 32, 40) of the fastening device (14, 15, 16); b) causing the anchoring portion (18, 23, 35, 40) to penetrate into the hydraulic structure or into the ground; c) laying down the protective membrane onto the surface area (11, 12) to be covered with the membrane fastening portion (22, 23', 35', 40') of the fastening devices (14, 15, 16) extending through respective holes in the membrane; characterised by: d) defining a plurality of punctual anchoring positions for the protective membrane by the individual fastening devices (14, 15, 16); e) positioning annular seals (27, 28) and locking plates (25, 26) with an annular frictional surface, to provide a frictional and sealing annular contact surface area on one side of the membrane; and f) anchoring the membrane to the individual punctual fastening devices (14, 15, 16) by sealingly pressing the same membrane against the surface area (11, 12) to be covered in a stretched condition, to transmit and distribute any force and stress acting on the membrane, to the individual punctual fastening devices (14, 15, 16) and to the hydraulic structure or to the ground through the annular seals (27, 28) and locking plates (25, 26). a) providing a plurality of punctual fastening devices (14, 15, 16) each comprising a punctual anchoring portion (18, 23, 32, 40) conformed to penetrate into the hydraulic structure or into the underlying ground, and a membrane fastening portion (22, 23', 35', 40') extending from the anchoring portion (18, 23, 32, 40) of the fastening device (14, 15, 16); b) causing the anchoring portion (18, 23, 35, 40) to penetrate into the hydraulic structure or into the ground; c) laying down the protective membrane onto the surface area (11, 12) to be covered with the membrane fastening portion (22, 23', 35', 40') of the fastening devices (14, 15, 16) extending through respective holes in the membrane; d) defining a plurality of punctual anchoring positions for the protective membrane by the individual fastening devices (14, 15, 16); e) positioning annular seals (27, 28) and locking plates (25, 26) with an annular frictional surface, to provide a frictional and sealing annular contact surface area on one side of the membrane; and f) anchoring the membrane to the individual punctual fastening devices (14, 15, 16) by sealingly pressing the same membrane against the surface area (11, 12) to be covered in a stretched condition, to transmit and distribute any force and stress acting on the membrane, to the individual punctual fastening devices (14, 15, 16) and to the hydraulic structure or to the ground through the annular seals (27, 28) and locking plates (25, 26).