The vector based, freeform shoreline development model ShorelineS can efficiently simulate the development of a shoreline through the use of relatively simple bulk longshore transport formulas. This allows it to be multiple orders of magnitude more efficient compared to complex two-dimensional horizontal process-based models. The model does make some assumptions in order to be this efficient. One of these assumptions is the constant profile angle along the shoreline. This means the model does not account for bathymetry. The version of the ShorelineS model used is from 03/08/2023.

This study analyses the applicability of ShorelineS for simulation of a shoreline with a river mouth. To this extent a synthetic case of a shoreline with a river mouth is set up to analyse the model behaviour of ShorelineS in a simplified environment. The effect of many input parameters on the shoreline development is analysed. These parameters include wave parameters, channel parameters, transport parameters, model parameters, and relative sea level rise. The applicability is further tested in a more complex environment with a real-world case. For this, a hindcast is set up. The location of the hindcast is the shoreline of the Rhône delta. This is a wave dominated, sandy coast with a negligible tidal range. Data on the shoreline, the wave climate, the sediment budget, and the shoreline profile were required to get a successful hindcast.

The implementation of a river mouth in ShorelineS is done through specifying the river flow path as well as to what extent the channel should be kept. The sediment discharge is then approximated by a nourishment in the flow path that is pushed out to the shore. This approach was found to work well in a simplified environment through analysis of results from the synthetic case. The different simulations resulted in the expected model behaviour and the simulations were stable.

The results of the hindcast are mostly positive. The hindcast gets a good skill score and the simulations are mostly stable. The biggest differences between the simulated shoreline and the actual shoreline of the Rhône delta can be explained by the existence of relict sediment lobes along the shoreline. These lobes are the result of the combination of progradation and avulsion in the Rhône delta. They make the shoreline profile variable and provide time limited sediment sources.

ShorelineS cannot account for these naturally occurring lobes because of the assumption of the constant profile angle along the shoreline. Combining this with the fact that ShorelineS is incapable of simulating processes related to river dynamics such as avulsion and the forming of mouth bars limits the applicability of ShorelineS in environments governed by natural processes, such as the Rhône delta.

However, there is enough applicability for ShorelineS outside of these environments. When the shoreline is not governed by natural processes but is instead regulated by humans, a canal for instance, the results of the ShorelineS simulations will only get better. The big difference in time and cost efficiency compared to other models makes ShorelineS uniquely suited for applicability where the demand for accuracy of the simulation is lower. For instance, in data limited environments or on a global scale.