The flow of thin layers of a fluid is common in a large number of
industrial and biological areas. The development of accurate
models is essential for a proper understanding of these flows. We
review the modelling of thin films of fluids, possibly contaminated
with both insoluble and soluble surfactants, flowing over a curved
substrate. The models for thicker films incorporate the dynamical
effects of inertia. Our work using centre manifold techniques can
provide systematic estimates of the errors in any simulation. The
centre manifold approach has a clear modelling process and has the
flexibility to readily incorporate the complex physical mechanisms seen
in these fluid dynamics. Indeed the power of the approach is used
to derive, using the same basic algorithm, proposed models for large
scale turbulent flow such as floods.