Correlation between flood frequency and geomorphologic complexity of rivers network - A case study of Hangzhou China

- Established correlation model of flood frequency and fractal dimension.
- Investigated the effect of urbanization on flood disasters.
- Use fractal dimension to adjust geomorphologic complexity of river networks.
- Case study of Hangzhou.

SummaryUrban flooding is a combined product of the climate and watershed geomorphology. River system is one of the vital components of watershed geomorphology. The geomorphic characteristics of rivers have important effect on the formation of flooding. However, there have been few attempts so far to investigate the relationship between flooding frequency, the probability of flooding, and the geomorphological complexity of river system. Such relationship is essential in order to predict likely responses of flooding frequency to the large-scale changes in the complexity of the rivers network induced by accelerating urbanization around rivers. In this study we investigate the correlation between geomorphological characteristics of river system and the probability of flooding. Hangzhou city in China, which has suffered severe flooding, is chosen as a case study to evaluate this correlation and to investigate the impact of changes of drainage networks morphology on the local flooding. The fractal dimension, which is used to quantitatively assess geomorphological complexity of rivers network, is calculated by using box-counting method based on fractal geometry for eight sub rivers network in Hangzhou. A model based on the correlation of flooding frequency and fractal dimension is established. The model is applied to investigate the effect of the rapid urbanization induced changes of river geomorphology on the local flood frequency in two typical regions in Hangzhou. The results show that the flood frequency/event increases with the decrease of fractal dimension of the rivers network, indicating that the geomorphologic complexity of rivers network has an important effect on flooding. This research has great referential value for future flood quantitative investigations and provides new method for urban flood control and river system protection.