The IPython notebook $CLAW/apps/notebooks/riemann/shallow/ShallowWaterRiemannProblem.ipynb illustrates solutions in the phase plane for the shallow water equations. You can view the notebook via nbviewer, but to change the data and re-execute cells, you will need to be running the notebook.
I will discuss genuine nonlinearity and approximate Riemann solvers, following the 2011 slides for Lectures 17 and 19.