The hydrologic design values of specific design return period or frequency are random variables having certain distribution pattern, so there are some uncertainty in it.
指定设计重现期或频率的水文设计值为随机变数，有一定的分布规律，表明它有相应的不确定性。
2
The cryptic period of the hydrologic time series of tidal reaches of the Yangtze River and Xijiang River are analyzed with the applying of spectral analysis and the result is reasonable.