Fixed and Variable Roughness Regimes for Rapid Inundation Modelling

2D Hydraulic modelling has improved dramatically in recent years as software and hardware allow for larger, more detailed models to be constructed and run within workable timescales. The information required to construct complex models (such as LiDAR, land parcels data, etc.) is now readily available. Although detailed terrain information is generally used in these assessments, reservoir failure inundation modelling is normally carried out using a fixed roughness (n = 0.100) across the entire model domain. The study presented investigates the ramifications of various choices for modelling roughness within a 2D domain. A domain for a UK reservoir has been modelled using MIKE21 for five scenarios for which roughness is the only variable. This clearly demonstrates the differences in modelled velocities, and therefore depth-velocity product (the metric often adopted when determining the consequences of a reservoir failure).