82        Dune::FieldVector<Scalar, 2> shearStress(0.0);
 
   84        const Scalar artificialWaterDepth = this->
limitRoughH(roughnessHeight_, volVars.waterDepth());
 
   86        const Scalar c = pow(volVars.waterDepth() + artificialWaterDepth, 1.0/6.0) * 1.0/(manningN_);
 
   87        const Scalar uv = hypot(volVars.velocity(0), volVars.velocity(1));
 
   88        const Scalar dimensionlessFactor = gravity_/(c*c);
 
   90        shearStress[0] = dimensionlessFactor * volVars.velocity(0) * uv * volVars.density();
 
   91        shearStress[1] = dimensionlessFactor * volVars.velocity(1) * uv * volVars.density();