$$
b = \left( {{1 \over {G_{cell} }}} \right)^{{1 \over 2}}  \cdot \left( {{{Q_{plant} } \over {height_{channel} }}} \right)^{{3 \over 4}}  \cdot \left( {{{K_{90} } \over {2 \cdot \nu  \cdot \Pi _{cell} }}} \right)^{{1 \over 4}} 
$$