6. Conclusions
This study demonstrated the procedure of a quantitative danger degree evaluation model and the judgment of FLWLs for each flood season. An earth dam overtopping risk rate model for the calculation of dam overtopping probability in each stage of the flood season and in the whole flood season was established. Then, grade division and evaluation of the dam overtopping danger degree were conducted quantitatively, according to the four important characteristic values of the dam overtopping risk rate. The proposed model was applied to the Chengbihe Reservoir in China. The following conclusions are drawn: (1) The danger degree of the Chengbihe Reservoir under the design standard was 0.57, corresponding to a moderate danger level. (2) FLWL for the Chengbihe Reservoir staged operation can be recommended as follows: 185.00 m for the early and main flood seasons, and 185.00 me187.50 m for the later flood season. The quantitative model for danger degree evaluation of earth dam reservoir staged operation in the flood season can provide a theoretical basis for danger degree assessment of earth dam reservoirs under normal operating conditions as well as optimal FLWLs for reservoir staged operation during the flood season.
However, there were some limitations in this study: (1) The dam overtopping risk rate for each stage of the flood season was based on the conditional probability, regarding dam overtopping events as independent of one another in each stage of the flood season. In fact, inter-temporal floods were indeed correlated to each sub-season flood (Xiao, 2004), and appropriate ways to consider this correlation is still an issue that is worth studying. (2) In the Monte Carlo simulation method, it is important to generate random number flow for the given probability distribution. Generally, the efficiency of simple random sampling is low, and an efficient random number generator, which is both fast and highly accurate, should be used.
