ABSTRACT
An original technical solution was designed for the currently prepared project Dry Retention Reservoir Mělčany (Czech Republic). The approach permits migration permeability and thus meets the current environmental requirements for newly built in-stream hydraulic structures. The design envisages the construction of a 19-meter-high earthfill dam with a combined structure, which contains a migration passage, bottom outlets and spillway. Thus, it allows the protection of the downstream area up to 100-years-flood discharge. The approach to the stilling basin design downstream the combined object is unique. The concrete construction of the 6-meter deep stilling basin is filled with a riprap in which a shallow river channel is modelled to ensure migration permeability and continues through the dam. The riprap material has been designed to resist normal flow rates and, in flood situations, to create an equally large scour that will effectively dissipate the flowing water energy. A variety of known formulas and approaches can be used to predict the size and depth of a scour. However, the amplitude of the results is so wide that the results were unclear and unusable for the design of a particular situation. A physical hydraulic model was created to verify and optimize the proposed stone size and the expected range of scours, and finally, the results were generalized. Conclusions of the hydraulic research confirmed the proposed solution as reliable in terms of dissipating the kinetic energy of water concerning the stability of the downstream river channel.
