The construction of complementary spillways founded over earth dams is of great interest from the economic point of view, but raises some problems concerning the foundation deformability and the integrity of the spillway structures. Former studies of the authors showed that the use of stepped channel spillways lined with wedge-shaped pre-cast concrete blocks is a very attractive possibility to increase the discharge capacity of existent earth dams. The paper presents the most significant design criteria and construction aspects related to this type of spillways and mentions the issues where further research is still required. Cost estimates of wedge-shaped pre-cast concrete blocks spillways over earth dams, as a function of the dam height and of the design discharge, are included.
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