Forecasting relationships have been recognized as an important tool to be applied together,
or not, with complete numerical modelling in order to reconstruct the wave field in coastal areas
properly when the available wave data is limited. In recent years, the literature has offered several
comprehensive sets of field experiments investigating the form of the asymptotic, depth-limited
wind waves. This has made it possible to reformulate the original deep water equations, taking
into account the eects of water depth, if wind waves are locally generated in shallow and confined
basins. The present paper is an initial attempt to further contribute to the shallow water forecasting
curves which are currently available, also considering the role on the wave generation of a variable
equivalent bottom roughness. This can offer the possibility of applying shallow growth curves to a
broad variety of contexts, for which bed composition and forms can be different. Simple numerical
tests have been conducted to reproduce the fully developed conditions of wave motion with variable
roughness values. To validate the new set of equations, they have been applied to a real shallow lake
for which both experimental and numerical wave data is available. The comparison of the obtained
results is very encouraging in proceeding with this approach.
