Comparative Study On Design Flood Estimating Methods

Design flood estimation is the key content and important part of engineering hydrology. A great many of theories and methods of design flood estimation have been studied and applied by hydrologists, and lots of achievements and experience were obtained. This paper was part of the key research projects sponsored by the Ministry of Water Resources, "The assessment of reservoir design flood theories and flood control methods at home and broad". The main works and conclusions were summarized as follows:(1) Based on the review and summary of the available literatures and guidelines of design flood all over the world, the research advancements and existent problems for flood frequency analysis, flood estimation in un-gauged area and PMP/PMF estimators were analyzed and discussed.(2) The statistical experiment was applied to compare different parameter estimation methods for P-â…¢ distribution. The simulation results showed that: for the un-biasness property, numerical integral with single-weighted or double-weighted function performed well in the sequential series and L-moment(LM) was the best one in the series including historical flood respectively; LM was the best method in both series for the robustness property. LM could be expressed in terms of the linear combinations of order statistics and only made operation of one order sampling moments when it was applied to estimate parameters of some sort of distribution. Therefore, LM was little affected by the errors of several sample plots, and the results by the method of LM were more robust than the other ones.(3) Regional flood frequency analysis is a useful approach method that avoids the shortness of at-site sample series and estimates design flood for un-gauged area. Regional flood frequency analysis for un-gauged basins included selecting a pooling-group, estimating the index flood, deriving pooled growth curve and fitting flood frequency curve for tested basin. A case study on some sub-basins of Yangtze River and Han River indicated that this method was practicable and the further research and application was worthwhile.(4) The advancement of PMP/PMF estimation at home and abroad was introduced and analyzed. The results of PMP/PMF in several countries were compared. The reasons why the PMP/PMF estimators in China were larger than those of other countries were discussed. Some suggestions on the future research of PMP/PMF were also pointed out.