The publisher apologises that upon publication of the article, the second derivative on the right-hand side of equation 3.21 was mistyped and thus presented incorrectly as
(3.21)
\begin{equation}\frac{\textrm{d}}{{\textrm{d}x}}\left( {\int_0^H {\frac{{{u_{SS}}}}{{{\alpha^2}}}\,\textrm{d}y} } \right) = \frac{\textrm{d}}{{\textrm{d}x}}\left( {\frac{{\textrm{d}{p_{SS}}}}{{}}\textrm{d}x\frac{{{H^3}}}{{12}} + \frac{1}{2}\int_0^H {Fy(H - y)\,\textrm{d}y} } \right) = 0,\end{equation}

The correct equation should be as below
(3.21)
\begin{equation}\frac{\textrm{d}}{{\textrm{d}x}}\left( {\int_0^H {\frac{{{u_{SS}}}}{{{\alpha^2}}}\,\textrm{d}y} } \right) = \frac{\textrm{d}}{{\textrm{d}x}}\left( {\frac{{\textrm{d}{p_{SS}}}}{{\textrm{d}x}}\frac{{{H^3}}}{{12}} + \frac{1}{2}\int_0^H {Fy(H - y)\,\textrm{d}y} } \right) = 0,\end{equation}
