[flux][shallowwater] doc shallow water flux

Add the units of the water flux and momentum fluxes in the documentation.

dumux/flux/shallowwater/exactriemann.hh

@@ -43,6 +43,9 @@ struct RiemannSolution {
  * \ingroup ShallowWaterFlux
  * \brief Exact Riemann solver for Shallow water equations.
  *
+ * The computed water flux is given in m^2/s, the momentum
+ * fluxes are given in m^3/s^2.
+ *
  * This Riemann solver is described in the book
  * "Shock-capturing methods for free-surface shallow flows"
  * from Toro, 2001. We keep the notation for the variables

dumux/flux/shallowwater/riemannproblem.hh

@@ -51,6 +51,9 @@ namespace ShallowWater {
  * after Audusse but further solvers and reconstructions ca be
  * implemented.
  *
+ * The computed water flux (localFlux[0]) is given in m^2/s, the
+ * momentum fluxes (localFlux[1], localFlux[2]) are given in m^3/s^2.
+ *
  * \param waterDepthLeft water depth on the left side
  * \param waterDepthRight water depth on the right side
  * \param velocityXLeft veloctiyX on the left side

dumux/flux/shallowwaterflux.hh

@@ -49,6 +49,11 @@ public:
      *        Riemann solver after Torro and the reconstruction after
      *        Audusse and a flux limiter for small water depths.
      *
+     *        The computed water flux of the Riemann solver is given
+     *        in m^2/s, the momentum fluxes are given in m^3/s^2. The
+     *        Riemann flux is mltiplied by scv.area() to get the flux
+     *        over the face.
+     *
      * \todo The choice of the Riemann solver should be more flexible
      */
     template<class Problem, class FVElementGeometry, class ElementVolumeVariables>