  Until now the analysis of long wave runup on a plane beach has been focused
on finding its maximum value, failing to capture the existence of resonant
regimes. One-dimensional numerical simulations in the framework of the
Nonlinear Shallow Water Equations (NSWE) are used to investigate the Boundary
Value Problem (BVP) for plane and non-trivial beaches. Monochromatic waves, as
well as virtual wave-gage recordings from real tsunami simulations, are used as
forcing conditions to the BVP. Resonant phenomena between the incident
wavelength and the beach slope are found to occur, which result in enhanced
runup of non-leading waves. The evolution of energy reveals the existence of a
quasi-periodic state for the case of sinusoidal waves, the energy level of
which, as well as the time required to reach that state, depend on the incident
wavelength for a given beach slope. Dispersion is found to slightly reduce the
value of maximum runup, but not to change the overall picture. Runup
amplification occurs for both leading elevation and depression waves.
