GIS and Remote Sensing in Hydrology, Water Resources and Environment (Proceedings of ICGRHWE held at the Three Gorges Dam, China, September 2003). IAHS Publ. 289, 2004, 107-113

Study on L-moment estimations for log-normal distribution with historical flood data

YUANFANG CHEN1, SHENGBIN XU1, ZHIGUI SHA2, PIETER VAN GELDER3 & SHENG-HUA GU4

1 Department of Hydrology and Water Resources, Hohai University, Nanjing 210024, China

yfchen@mail.edu.cn

2 Bureau of Hydrology, Yangtze Water Resources Commission, Wuhan 430010,China

3 Faculty of Civil Engineering and Geosciences, Delft 2600 GA, The Netherlands

4 Shanghai Hydrological General Station, Shanghai 200232,China

Abstract This study is focused on a parameter estimation method for log-normal distribution based on L-moments. The relationship between L-moments and parameters of a common log-normal distribution is briefly introduced, then two sample formulae of L-moments, taking into account historical flood data, are proposed. The Monte-Carlo calculations show that both of them are of high accuracy in the estimation of parameters and quantiles (design values). Comparisons of the ordinary moments method, the curve-fitting method with absolute norm and the L-moment estimation method are also carried out using Monte-Carlo experiments. The results show that L-moment estimation is the preferred method and is therefore recommended to be used in practice.

Key words bias; curve-fitting method; effectiveness; historical flood; L-moment; log-normal; moment method