The purpose of the research is to analyze existing designs of spillway constructions and develop recommendations on applying reserve spillways for earth dams at the river hydro systems. To decrease the cost of spillway constructions in some cases several spillways are provided. One of them is the main and one or two others are auxiliary (reserve). The main spillway is calculated for flood discharge of more frequent repeatability and the reserve ones for discharge of the rare repeatability. The use of reserve spillways at the example of Eppalock, Australia, and Box Butte, USA, is considered. The main spillway of Eppalock hydro system is designed as an open coastal chute, which is calculated for discharge of the repeatability 1 time in 100 years, and one of the reserve spillways is designed for discharge of the repeatability 1 time in 1000 years, and another one reserve spillway for the discharge of the repeatability 1 time in 10000 years. The brief description of reserve spillways with scoured inserts is given. Those spillways are protected by copyrights and patents for inventions. The description of the rapid built reserve spillway at a low-head hydro system is also presented, which is an artificial closure channel of trapezoidal section protected from scouring by geomembrane. One of the main requirements for reserve spillways is the simplicity of design and low cost of the construction. To increase the operation efficiency of the spillway, scouring inserts with the mark of a surcharged reservoir level at the top of a dam or slightly lower are included.
Keywords: reserve spillway, earth dam, flood discharge, frequent and rare repeatability, scouring earth insect.
