Abstract: Distributed hydrological modeling is a hot issue in current hydrological research. This study applies a digital watershed model to a small watershed of the upper Yangtze. First, the ArcGIS code is used to extract river network information. We select the rainfall and flood series of the river basin of 1982, and calibrate and verify the model parameters using a graphical method based on factor analysis. The calibration gives a Nash efficiency coefficient of 0.97 and peak errors within 10%, indicating that the model can well simulate the runoff yield and flow concentration in this small watershed. Then, a sensitivity analysis is made on several key parameters involved in the model. The results show that vertical saturated hydraulic conductivity affects the flood peak only and the two parameters are negatively correlated. The initial water content of soil affects the runoff only, with a positive correlation; field capacity is negatively correlated with the flood peak and runoff process; vegetation water interception is negatively correlated with the flood peak and runoff; and roughness, negatively correlated with the peak value, affects the shape of flood peak only. We suggest that further validation with recent measurements be needed before the model is applied to the engineering problems in the study area.

Key words: digital watershed model, parameter calibration, sensitivity analysis, Long River basin, upper Yangtze River