The purpose of research is the development of calculation methods of main parameters of rectangular reserve spillway for passing rare flood discharges for Class IV dams, allowing determining the time of its full cross-section inclusion in a work. Reserve spillways are used to reduce the cost of the main spillway. Reserve spillways should be simple structurally and low cost. The composition of the reserve spillway may include the scoured insert, which is a disposed on the concrete sill spoil, eroded by water level rising in the upstream up to the highest water level deadline (HWL). Discharged water flow may be directed downstream by natural degradation or worked out cut, which can be protected from erosion depending on predicted consequences of flood passing. The article describes the design of reserve spillway with the scoured insert, which is simple to manufacture and consists of a rectangular or trapezoidal surface which fixes washout; its material may be concrete, asphalt, and so on. Inside the spillway at some critical point there are rectangular or another shapes watercourses for the start of subsoil washing out. In developing the calculation methods of the basic parameters of the reserve spillway with scoured insert conventional methods for the hydraulic calculations weirs, as well as the method of hydraulic calculation of spillways were used. To test the method, the article describes an example explaining the peculiarities of calculation of reserve spillway main parameters in which the width of the spillway is 3.0 m, the flushing velocity is 2.1 m/s, the specific consumption is 1.05 m²/s and the time of its inclusion (washing out) in work is 47.9 minutes. The method of calculation allows determining the main parameters of the reserve spillway and the time of its inclusion by total cross section in work.
Keywords: reserve spillway, a dam, flow intensity, flushing velocity, hydraulic radius, slope, median fall diameter, flooding.
