\large
$$
D = 0.66\left[ {\varepsilon ^{1.25} \left( {{{LQ^2 } \over {gh_{\rm{f}} }}} \right)^{4.75}  + \nu Q^{9.4} \left( {{L \over {gh_{\rm{f}} }}} \right)^{5.2} } \right]^{0.04} 
$$