# Multi-Hazard WebGIS Platform for Coastal Regions
## 2 Materials and Methods
### Multi-Hazard Framework for Flood and Erosion Risk in Coastal Zones
#### 2.1.2 Modeling and Forecasting Infrastructure  
For selected observatories, model predictions can be generated using the OPENCoastS forecast service [20]. This service can be used to forecast the circulation in any coastal area worldwide at the choice of the user, supported by the Water Information Forecast Framework (WIFF, [12; 21]) and the European Open Science Cloud resources ([[https://www.eosc-hub.eu/](https://www.eosc-hub.eu/)]([https://www.eosc-hub.eu/](https://www.eosc-hub.eu/)) (accessed on 10 May 2021)). WIFF was expanded to address the prediction of multiple coastal hazards, including a real-time beach morphodynamic module, based on a combination of models: SCHISM [22] and XBeach [23].  
The open-source modeling suite SCHISM solves the three-dimensional shallow water equations using unstructured grids [22]. Here, the SCHISM modelling system uses a single unstructured grid to discretize the horizontal space, in depth averaged (2 DH) mode, with a two-way coupling between the circulation and wave modules. It provides the free-surface elevation and the 2D water velocity fields using finite-element and finite-volume schemes, and model WWM provides the wave parameters. SCHISM is a highly efficient, parallelized model, a fundamental property for forecast applications.  
The open-source hydro-morphodynamic model XBeach [23] was originally developed to assess the natural coastal response to the time-varying storm and hurricane conditions. The main model highlight was to account for the variations of the surface elevation and of the short-wave energy at the wave group timescale. Compared to SCHISM, this still allows modeling the generation and/or propagation of infragravity waves (i.e., long-waves with periods greater than 25 s). By solving the non-stationary shallow water equations, the sediment transport equations, and the continuity equation for the bed update, it can model long-wave runup, dune erosion, overwashing and breaching. Since its original development, several improvements have been implemented in new releases and it can be applied in three different modes, stationary, surfbeat and non-hydrostatic, which account differently for infragravity waves and short-waves [24].  
In the MOSAIC platform, XBeach is used in hydrostatic \"surfbeat\" mode. SCHISM and XBeach configurations run consecutively, with SCHISM providing the necessary boundary conditions to run XBeach. This nesting procedure enables running XBeach in a smaller domain, possibly with a higher resolution at the shoreline.  
The SCHISM configuration was previously calibrated and validated based on historical data and a dedicated field campaign [25]. It was run over a single triangular grid composed of 49,684 nodes and 94,892 elements, with an edge length ranging from 2 km offshore to 20 m in the nearshore, harbor and river area. The field data were also used to evaluate the short-wave breaking and the representation of the infragravity wave component in the XBeach configuration. Both model configurations were then used in WIFF to produce daily predictions of circulation and morphodynamics.  
In order to obtain boundary conditions at the local coastal scale, a chain of models is used to address the several spatial scales and processes to be solved. This approach is generic and can be applied to any coastal system. The specific forcing providers shown in Figure 1 (ARPEGE, GFS, FES2014) can be replaced by other providers (e.g., high resolution WRF forecasts).  
The model workflow encompasses several steps (Figure 1), where each model is forced by outputs from the previous one, from the regional scale to the coastline. In the future, these predictions will be integrated with online field data to provide enhanced, assimilated forecasts.