  The solution of an extended Riemann problem is used to provide the internal
boundary conditions at a junction when simulating one-dimensional flow through
an open channel network. The proposed approach, compared to classic junction
models, does not require the tuning of semi-empirical coefficients and it is
theoretically well-founded. The Riemann problem approach is validated using
experimental data, two-dimensional model results and analytical solutions. In
particular, a set of experimental data is used to test each model under
subcritical steady flow conditions, and different channel junctions are
considered, with both continuous and discontinuous bottom elevation. Moreover,
the numerical results are compared with analytical solutions in a star network
to test unsteady conditions. Satisfactory results are obtained for all the
simulations, and particularly for Y-shaped networks and for cases involving
variations in channels' bottom and width. By contrast, classic models suffer
when geometrical channel effects are involved.
