87        Dune::FieldVector<Scalar, 2> shearStress(0.0);
 
   89        const Scalar artificialWaterDepth = this->
limitRoughH(roughnessHeight_, volVars.waterDepth());
 
   90        const Scalar karmanConstant = 0.41; 
 
   91        const Scalar dimensionlessFactor = power(karmanConstant, 2)/power(log((12*(volVars.waterDepth() + artificialWaterDepth))/ks_), 2);
 
   92        const Scalar uv = hypot(volVars.velocity(0),volVars.velocity(1));
 
   94        shearStress[0] = dimensionlessFactor * volVars.velocity(0) * uv * volVars.density();
 
   95        shearStress[1] = dimensionlessFactor * volVars.velocity(1) * uv * volVars.density();