Extreme flood abatement in large dams with gate-controlled spillways

•We evaluated the flood abatement effects of dams with gate-controlled spillways.•We analyzed the abatement behavior of 355 configurations of dams and reservoirs under stochastic hydrological forcing.•A strong bi-linear correlation between peak inflow and peak outflow was found.•We obtained expressions that establish a relationship in terms of adimensional coefficients.•The results allowed for the characterization of the flood abatement behavior.

SummaryIn this study the flood abatement effect at dams with gated spillways under a wide range of extreme floods is analysed (100 < return period <10,000 years). A group of integrated models (rainfall generator, hydrological model and dam operation model) interacting within a Monte Carlo simulation framework is used for producing numerous hydrologic events at 21 sites across mainland Spain, and the hydrologic response applied to 81 configurations of dams and reservoirs. Common behavioural patterns are identified and dimensionless coefficients classified, based on the hydrologic variables and the dam and reservoir characteristics. The relationships between these coefficients are analysed, with a significant degree of correlation both among the cases and the varying magnitude of floods being obtained. Finally, models that enable evaluation of the abatement capacity of a dam with a gated spillway in the event of a flood with Tr between 500 and 10,000 years are offered. In addition, they allow the frequency curve of such a maximum flow to be obtained, something which could serve of use not only during the design phase but also in the evaluation of the hydrologic safety of dams.