30        using VolumeVariables = 
typename OutputModule::VolumeVariables;
 
   32        out.addVolumeVariable([](
const VolumeVariables& v){ 
return v.waterDepth(); }, 
"waterDepth");
 
   33        out.addVolumeVariable([](
const VolumeVariables& v){ 
return v.velocity(0); }, 
"velocityX");
 
   34        out.addVolumeVariable([](
const VolumeVariables& v){ 
return v.velocity(1); }, 
"velocityY");
 
   35        out.addVolumeVariable([](
const VolumeVariables& v){ 
return v.bedSurface(); }, 
"bedSurface");
 
   36        out.addVolumeVariable([](
const VolumeVariables& v){ 
return v.bedSurface() + v.waterDepth(); }, 
"freeSurface");