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.

It can be seen that the frequency curve calculation is basically reasonable and show the estimation of "1482 flood" return period is rational after putting palaeofloods into flood series.

Based on the flood level frequency curve, hydrological failure risk was divided into flood overflowing risk and flood overtopping risk.