  In this paper, we introduce a new extended version of the shallow water
equations with surface tension which is skew-symmetric with respect to the L2
scalar product and allows for large gradients of fluid height. This result is a
generalization of the results published by P. Noble and J.-P. Vila in [SIAM J.
Num. Anal. (2016)] and by D. Bresch, F. Couderc, P. Noble and J.P. Vila in
[C.R. Acad. Sciences Paris (2016)] which are restricted to quadratic forms of
the capillary energy respectively in the one dimensional and two dimensional
setting.This is also an improvement of the results by J. Lallement, P.
Villedieu et al. published in [AIAA Aviation Forum 2018] where the augmented
version is not skew-symetric with respect to the L2 scalar product. Based on
this new formulation, we propose a new numerical scheme and perform a nonlinear
stability analysis.Various numerical simulations of the shallow water equations
are presented to show differences between quadratic (w.r.t the gradient of the
height) and general surface tension energy when high gradients of the fluid
height occur.
