Abstract:

The influence of river network fractal characteristic on runoff was studied.The studyareas are eight basins controlled by eight hydrostations respectively， located in the upper and middle courses of Gan River.The river network characteristic is described by the fractal dimension， and the characteristic of runoff series is described by the Hurst exponent.Then the relationship between the river fractal dimension and the Hurst exponent was analyzed.And the influence of river network characteristic and the river network changes on the flood/drought are analyzed.The result shows that the higher the river network fractal dimension is， the more complex the river network will be， which is represented by higher Hurst exponent of runoff depth， so the runoff process is more simple.The complexity of runoff series can reflect the probability of flood/drought happening.Generally speaking， the higher the river network fractal dimension is，the lower the probability of flood/drought happening will be.The relationship between the river network fractal dimensions and the Hurst exponents of runoff depth indicates that when physical geography conditions' changes are not obvious， the degeneration of river network can result in higher probability of flood/drought happening.

Key words: upper and middle course of Gan River, river network characteristic, fractal dimension, runoff depth, Hurst exponent