Hydrological Risk Analysis of Dams: The Influence of Initial Reservoir Level Conditions

Abstract

In this paper, we present a method to assess the influence of the initial reservoir level in hydrological dam safety and risk analysis. Traditionally, in professional practice, the procedures applied are basically deterministic. Several physical processes are defined deterministically, according to the criteria of the designer (usually in the conservative side), although there is a high degree of uncertainty regarding these processes. A relevant variable is the reservoir level considered at the beginning of flood events. Hydrological dam safety assessment methods traditionally assume that the reservoir is initially full when it receives the design flood, thus, staying in the conservative side when designing a new dam. However, the distribution of reservoir levels at the beginning of flood episodes takes more importance for evaluating the real risk for the dams in operation. We analyzed three different scenarios—initial reservoir level equal to maximum normal level, equal to a maximum conservation level, and following the probability distribution from the historical records. To do so, we presented a method applied to a gated-spillway dam located in the Tagus river basin. A set of 100,000 inflow hydrographs was generated through a Monte Carlo procedure, by reproducing the statistics of the main observed hydrograph characteristics—peak flow, volume, and duration. The set of 100,000 hydrographs was routed through the reservoir applying the Volumetric Evaluation Method as a flood control strategy. In order to compare the three scenarios, we applied an economic global risk index. The index combines the hydrological risk for the dam, linked to the maximum water level reached in the reservoir, during the flood routing, and the flood risk in the downstream river reach, linked to the discharge releases from the dam. The results showed the importance of accounting for the fluctuation of initial reservoir levels, for assessing the risk related to hydrological dam safety. Furthermore, a procedure to quantify the uncertainty associated with the effects of initial reservoir level on hydrological dam safety, has been proposed.

Hydrodynamic Performance and Design Evolution of Wedge-Shaped Blocks for Dam Protection against Overtopping

“…Since 2011, new research efforts have aimed to complement the theoretical and practical knowledge of WSB technology [27][28][29][30][31]. Such work aims to deepen our knowledge on an alternative technology in order to improve dam safety, which is particularly threatened by the hydrological consequences of climate change [32][33][34][35][36][37][38][39]. Specifically, the main goal of the research was to increase the cost efficiency of the discharge capacity of existing spillways and the protection of earth dams against potential overtopping.…”

Flood Control Versus Water Conservation in Reservoirs: A New Policy to Allocate Available Storage

“…However, it can reduce the volume of water available to satisfy the demands of the water supply system because it influences the definition of MCLs. Accounting for the variability of the initial reservoir level in a hydrological dam and its downstream safety leads to more realistic results [8,[12][13][14], which consequently can improve the definition of MCLs. Within this study, we propose a stochastic methodology to determine seasonal MCLs.…”

Avaliação de métodos de interpolação em dados de batimetria na barragem do rio Poxim-Açu – SE

“…No processo de construção de barragens, a água é represada e áreas são alagadas, formando uma extensa lâmina d'água sobre a superfície do terreno. O volume de água que é armazenado nessas barragens está em função da área da lâmina d'água e a profundidade do lago, tecnicamente denominada batimetria (Gabriel-Martin et al, 2019;Lang et al, 2019;Stähly et al, 2019). Os valores de batimetria de uma barragem são monitorados constantemente, com o objetivo de assegurar a quantidade e qualidade de água disponível.…”