On a momentum conservative z-layer unstructured C-grid ocean model with flooding

We present a z-layer unstructured C-grid finite volume hydrostatic model. An efficient and highly scalable implicit technique for solution of the free surface equation is combined with an Eulerian approach for the advection of momentum. We show that an accurate velocity reconstruction procedure is of crucial importance not only for discretization of the Coriolis term, but also for the correct advection of momentum, especially in the multilayer case. Unlike other z-layer models the method presented here ensures that the staircase representation of bathymetry and free surface has no influence on the vertical structure of the flow. The method is therefore guaranteed to be strictly momentum conservative, also in the layers containing the free surface and bed. A number of test cases are presented to show that the model is able to accurately simulate Coriolis dominated flows and flooding and drying processes both in the depth-averaged case and in the presence of multiple z-layers. We use a simulation of 2004 Indian Ocean tsunami to evaluate the ability of the method to simulate fast propagating tsunami waves and detailed inundation processes. Results obtained using two different rupture models are compared to the tide gauge arrival times, satellite altimetry data and the inundation observations in the Banda Aceh area. The comparison is used not only to assess the quality of the underlying rupture models but also to determine the value of the available data sources for such an assessment.