Investigating land cover effects on tsunami overland flow dynamics using HEC-RAS model

Abstract

This study investigates the impact of land use and land cover on tsunami inundation characteristics in a coastal area of the Galle District, Sri Lanka, which was heavily affected by the 2004 Indian Ocean tsunami. The research addresses the underexplored role of surface features in altering tsunami behavior, particularly arrival time, depth, velocity, and inundation extent. Using the HEC-RAS 2D hydrodynamic model and high-resolution topographic and bathymetric data, seven scenarios were simulated, including historical and present land cover conditions, forested and urban areas, bare land, elevated building features, and coastal vegetation buffers. The tsunami wave was modeled using a stage hydrograph based on the 2004 event. Model validation against historical hazard maps showed a good fit, confirming model reliability. Results indicate that higher surface roughness significantly reduces wave depth, velocity, and inland inundation. Buildings modeled as elevated features result in more accurate models because they affect flow paths, and coastal vegetation belts offer improved wave resistance. The study concludes that land cover plays a critical role in tsunami impact reduction and should be integrated into hazard mapping and development planning. These findings provide a practical approach for enhancing disaster preparedness and urban planning in vulnerable coastal zones.