The impacts of impervious surface expansion and the operation of polders on flooding under rapid urbanization processes

Impervious surface expansion and the construction of polders are typical human activities that can influence hydrological processes. Understanding the mechanism of the influence can help to establish flood control within a changing environment. In this study, the influence of impervious surface expansion and the operation of polders on flooding have been detected using a semi-distributed hydrological model, i.e., the Hydrological Engineering Center-Hydrological Modeling System (HEC-HMS) model. The results indicate that impervious upstream surface expansion influenced peak discharge more significantly compared with downstream expansion. The peak discharge of the basin with polders decreased 26.38–36.61% compared with that without polders. Impervious surface expansion effected a higher increase in the peak discharge in a basin with than without polders. A decrease in drainage discharge and an increase in the maximum allowable water depth could reduce peak discharge at the basin outlet. On the premise of ensuring safety inside polders, polder operation could help reduce on average 7.94% and 5.90% of small and large floods peak discharge on average.