Abstract: The Three Gorges Interval (TGI) accounts for 5.6% of the upper Yangtze River basin area. However, floods originating from this region constitute over 10% of the floods in the Three Gorges Reservoir (TGR). Hence, heavy rainfall-induced flood is an important factor that must be taken into consideration in ensuring reservoir flood control safety. Based on TGR inflow data during 2007-2011 and flow data from upstream Cuntan and Wulong stations, we developed a HEC-HMS flood simulation model to examine the correlation between rainstorm floods in the TGI and inflow floods into the reservoir. We proposed an interval flood modeling scheme based on classified parameter adjustment and staged testing according to flood sources: for floods primarily driven by upstream inflows, the flood confluence parameters were calibrated; for floods predominantly influenced by regional precipitation,the flow yield parameters were calibrated. To validate the model, we compared simulated flood processes post-2012 with operational records of the TGR, demonstrating model accuracy with the relative errors of peak flow rate in calibration and verification periods within ±20% and peak time errors below 3 hours. Comparisons with Three Gorges Project (TGP) operation records confirmed the model’s suitability for simulating post-2012 TGR flood processes. Examining the flood event on June 26, 2016, as a representative case, we observed a significant 27.2% contribution rate of flood peak within the reservoir, with a peak time advance of 16 hours. These findings facilitate understanding TGR flood impacts and serve as a technical reference for flood modeling schemes within the basin region.

Key words: Three Gorges region, flood process simulation, HEC-HMS model, parameter calibration