A new smoothed particle hydrodynamics (SPH) scheme that simulates floating debris in shallow water tsunami flows will be presented. The scheme is developed for debris-laden tsunami flows, one of the most deadly natural disasters, causing enormous destruction and loss of life. The debris transported by the violent surges has a significant role in destroying the inland structures. This research investigates the debris behaviour in shallow water flows, such as tsunami and urban floods, to mitigate future flooding events. SPH is a meshless Lagrangian discretization scheme whose major advantage is the absence of a mesh making the method ideal for highly non-linear flows with mixing of fluid and debris components which change with time. Two new formulations to include floating debris are proposed that capture two-way debris-fluid coupling [1] within both the depth-averaged approach and the particle method of SPH. The hydrodynamic forces acting on the debris are formulated in a three-dimensional (3-D) approach such that the debris can move in the vertical direction within the water column. The model can predict debris-debris, debris-bed and debris-wall interaction. The new SWE-SPH debris models are validated using a range of test benchmark cases with increasingly complex geometries including a floating debris in a hydrostatic tank with sloping bed, debris moving in uniform flow down a sloping channel, debris hit by a dam break surge and debris flow along a channel with side baffles comparing with experimental data. The SWE-SPH-debris model is applied in the Okushiri tsunami case where tens of individual debris are distributed throughout the domain near the shoreline. The results highlight the different behaviour observed for debris with density greater than or less than water. REFERENCES [1] Aslami, M.H., Rogers, B.D., Stansby, P.K., Bottacin-Busolin, A., 2023, Simulation of floating debris in SPH shallow water flow model with tsunami application, Advances in Water Resources, 2023, 171, 104363, doi:10.1016/j.advwatres.2022.104363.