By conducting three-dimensional generalized physical model experiments on gravelly soil landslides in the Three Gorges Reservoir area at the confluence reaches of main and tributary streams,we explore the surge run-up characteristics of river-type reservoir confluence reaches under hydrostatic conditions.Using a dimensionless analysis method,we study the influence of three factors including landslide volume,slope angle,and water depth on the maximum relative run-up height in the straight reach on the opposite bank,and derive a predictive formula for the maximum run-up height of gravelly soil landslides under hydrodynamic boundary conditions by the multiple regression analysis method.The results indicate that relative run-up height shows a positive correlation with all three factors.In the same-bank straight section,comparing surge run-up height attenuation laws at identical distances (1-3 m) but different directions reveal that both directions follow exponential attenuation within a certain distance.The mean surge run-up height against the river channel is about 9.8% greater than that along the river channel.Beyond a certain propagation distance (1-3 m),varying degrees of run-up height increase occur.In the tributary stream section,under consistent propagation distances from upstream/downstream landslides to the tributary inlet and consistent surge incidence angles,the surge run-up hazard level on the left bank of the tributary is greater than that on the right bank for both upstream and downstream landslides.