Performance of the complex spillway structure after gate replacement - physical modelling

Abstract

The recently applied stricter demands on the safety of dams as well as on their operation resulted in the design of adjustments, enhancements and reconstructions of many spillways on large dams in the Czech Republic. The physical and/or numerical modelling of the suggested designs are usually applied due to the complex hydraulic conditions either on the spillway structure itself or in the reservoir area. The paper presents the results of the physical and numerical modelling of the spillway structure of the Nechranice Dam. The original structure consisted of three sections of spillway gated by drum gates. As the original structure did not meet the requirements during both normal and flood operation, replacement of both outer drum gates by the flap gates was proposed. The change in the gate type also caused major changes in the concrete spillway structure. Due to the presence of the perforated vertical wall breakwater in the reservoir, modelling was necessary to quantify, in the form of capacity curves, the performance of the spillway in different operation schemes. The paper also presents commented comparison of the results obtained in the laboratory and from numerical modelling.