Abstract: The construction of large-scale cascade hydropower projects in mountainous area of west China has encountered new problems in complex circumstances, such as design standards for river diversion and closure and risk control, safe hydraulic control of steep slope tunnel diversion, safe and economic hydraulic control of river bed closure with thick overburden layer, and predictive control of disasters in river diversion and closure process, among others. After 28 years of systematic research, some technical problems related to hydraulic control and disaster reduction for large-scale cascade hydropower projects have been solved. The achievements are presented as follows: (1) A risk assessment model of diversion system and a decision-making model for the standard of river closure based on real-time hydrological monitoring and forecasting were built for synchronous construction of multiple cascade projects; standard selection methods were proposed to meet safety and economy requirements, and design specifications of construction diversion were modified. (2) The causes and mechanisms of adverse hydraulic characteristics such as alternative free surface and pressure flow in steep-slope tunnels were revealed; some composite hydraulic control techniques were proposed to guarantee tunnel safety, including obstructive floating embankment for vortex reduction in the upstream of tunnel inlet, inlet form with sharp edges alleviating alternative free surface and pressure flow in tunnel, and outlet form with downward slope for increasing pressure in tunnel; an innovative protection technology has addressed the safety problem in flood season in the presence of large flow and thick cover layer by adopting flexible blanket of reinforced cage and multi-stage flow rectifying for overflow cofferdam. (3) An innovative and practical formula for the stability calculation of natural closure blocks was proposed in consideration of water depth, flow velocity distribution, river bed roughness, and circumfluence coefficient; a formula for the stability calculation of artificial closure block of hexahedron stone-gabion reinforced cage was also established. Both the formulae are of good precision close to practice. (4) A tetrahedral reinforced cage with infiltrated geomembrane embedded and a new type of river closure material of cylindrical line bar were invented. (5) The technology of “wide underwater dike” was proposed to reduce river closure difficulty. (6) The second surge in the process of high-steep bank landslide was defined as the first wave for the first time; a practical formula for the height of first wave was obtained, and a model for predicting the generating and spreading of surges was built. (7) A high-resolution technology for simulating the process of earth-rock cofferdam breaking and flood routing was developed. These key technologies have boosted the development of relative disciplines and stimulated the technological progress in water conservancy and hydropower industry.

Key words: large-scale water conservancy and hydropower project, hydraulic control of river diversion and closure, disaster prediction control, alternative free surface and pressure flow, risk assessment, wide underwater dike, first wave height, mountainous area in west China