The announced depletion of fossil energy resources is fueling some speculation. It is therefore urgent to explore the different renewable energy sources available to Benin. In the ocean, in addition to swells, there are also orbital marine currents generated by them. An advantageous solution for the countries located in the Gulf of Guinea is the recovery and transformation of the energy of the swell and its orbital marine currents into electrical energy. Swells are adult waves that propagate freely at the atmosphere-ocean interface. In this work, based on measurements made by the Millenium Challenge Account (MCA-Benin) as part of the extension of the Autonomous Port of Cotonou, we have shown that the swells at the Autonomous Port of Cotonou are Airy swells or of Stokes. We have identified the modified Boussinesq equations, proposed by Peregrine in 1967, as the theory for characterizing the evolution of these swells during their formation in the coastal zone. The variations of the different wave parameters (height, wavelength, period, phase and group velocities) are characterized from the shoaling zone to the breaking point. With this theory the results obtained are in agreement with the experimental measurements made, they perfectly describe the amplification of the height of these waves and show that these swells become very energetic when they approach the coast.