Wide, healthy and safe sandy beaches are of major interest from the perspective of recreational and economic activity. In addition, sandy beaches are a strategic location for navy activities (unloading of troops, equipment or supplies; infrastructure protection; land mine detection). Yet, among all the different types of coasts (sandy, muddy and rocky), wave-dominated sandy beaches are the most unpredictable, dynamic and poorly understood coastal systems. Our project aims at improving our understanding of sandy coast behaviour. The numerical modelling and data collection approach proposed in the frame of CHIPO relies on an in-depth literature review, over the last 15 years, of scientific advances in sandy beach morphodynamics and long-term coastal evolution in which the contribution of our research group is internationally acknowledged. A fundamental step that we identified is that combining cross-shore and longshore processes will drastically improve our understanding and ability to predict three-dimensional sandy beach morphodynamics and long-term shoreline variability. Until now, cross-shore and longshore processes have been addressed in isolation worldwide. This combination, which is arguably a necessary requirement to understand and predict coastal evolution, is the common thread of CHIPO. Our project relies on the development of two numerical models, which will be unique in the international scientific community, and long-term shoreline data. The main field site is the Aquitaine coast but, in the framework of international collaborations, we will also use long-term shoreline data from seven international beaches spanning a wide range of environmental variables (wave climate, sediment grain size, geological constraints). Combining innovative numerical modelling and this dataset, the primary objectives of CHIPO are (1) to identify the respective contributions of cross-shore and longshore processes to both sandy beach morphodynamics and long-term shoreline evolution, (2) to develop two state-of-the-art efficient numerical tools and (3) improve our understanding and ability to simulate and further predict coastal evolution on timescales ranging from a few hours to decades. CHIPO is innovative because it paves a gap in the French scientific community as no research group currently addresses the numerical modelling of long-term coastal evolution. In addition, French research groups essentially rely on complex process-based modelling. Here, in the frame of long-term modelling, behaviour-oriented and cellular automaton will be developed which will allow us to (1) perform long-term simulations with reasonable computation cost and (2) avoid the effects of the misspecifications of the physics that inevitably cascade up through the scales in complex process-based nonlinear models and result in unreliable simulations on long timescales. Our project, which builds on an in-depth literature review and the clear identification of scientific problems, is both efficient and inexpensive, and relies the internationally-acknowledged expertise of a group of productive young researchers (according to ANR’s definition). CHIPO will lead to strong scientific advances and outreach activities (dissemination, public engagement, knowledge exchange) and engagement with the public and private stakeholders will be a priority of CHIPO. The numerical models developed within the framework of CHIPO will be made available for the ECORS demonstrator.