The scientists developed a model to predict how coastlines change over time due to sand movement. They improved the model to include factors like dune erosion and sand exchange between different beach areas. The model accurately predicted changes in two real-world locations: Westhampton Beach in the US and Macaneta Spit in Mozambique. It successfully showed how a new structure at Westhampton Beach caused the shoreline to advance, and how waves and water levels affect the shape of the beach at Macaneta Spit. Overall, the model can make reliable predictions about coastal changes over decades in just a few minutes on a regular computer.