Improvement of the design of a high-head spillway is impossible without consideration of the occurrence of cavitation, cavitation erosion of the spillway surface, and aeration of the flow. Knowledge gained about the regularities of air entrainment on spillways and experience in operating aerating devices enable the designer to control aeration of a high-velocity flow within certain limits. To prevent the development of cavitation erosion of the material of the spillway surface, on the entire length of the cavitation-hazardous section of the spillway passage it is necessary to form an aerated flow with a volume air concentration in the boundary layer with thickness 0.2-0.25 m of not less [1] than 7-8%. Here it is desirable, as far as possible, to avoid an extreme increase of the depth of the flow being discharged, which "swells" from the air being transported, in order to prevent overflowing the sides of the spillway or a decrease of the discharge capacity of a spillway tunnel as a result of its transition into a pressure operating regime.As is known [2], in a liquid flow a local decrease of pressure leading to cavitation and cavitation erosion of the material of the spillway surface occurs most often as a result of curving of streamlines during flow of a high-velocity stream past local roughnesses of the concrete spillway surface. As a rule, typical roughnesses of a technological nature become the source of cavitation erosion. For instance, in the case of concreting with the use of wood and metal formwork secured in place by reinforcing bars, typical roughnesses of the concrete surface in the form of a projection or ledge across the flow with a height up to 30-60 mm were recorded [3] at the Places of the joints of the forms on various spillways. Experience in flattening individual large roughnesses and imparting erosion-free outlines to them on the bucket of the spillway dam of the Krasnoyarsk hydroelectric station showed [3] that even with the aid of means of mechanizing the works it was not possible to obtain slopes of the faces more gentle than 1:12 for roughnesses with a height of 20-40 mm and more gentle than 1:20 for roughnesses with a height of 5-20 mm. Such slopes still provided an erosion-free operating regime of the spillway for heads from the upper pool level (UPL) at the site less than 50 and 70 m, respectively (Fig. 1). Intense cavitation erosion of the spillway surface was observed at a distance of more than 60 m from the spillway inlet with a slope of the spillway face of 0.79.Air entrainment into a turbulent water flow occurs as a result of breaking of waves and disturbances at the water-air interface due to mutual diffusion penetration of the two media. Therefore natural self-aeration of the flow is possible only below the point of emergence of the turbulent boundary layer onto the free surface (Fig. 2). The length of the initial section [4, 5] of development of the boundary layer xs=h ~ _~3z (1+ 1,3V,2o)1o 2]~+l.svz0 (1) is greater, the greater the depth of the flow, and, consequently, the spe...