According to bernoulli equation
$$ P_1+1/2 \rho v_1^2+ \gamma h_1= P_2+1/2 \rho v_2^2+ \gamma h_2. $$
Because $$ v_1=0\quad h_1=0 $$ So $$ 0= 1/2 \rho V^2+ \gamma h. $$ It is wrong I know, but why? Please help, thanks.
After a short time to review my book, I have an idea. The $\gamma h$ in bernoulli equation cannot be seen as pressure. It must be seen as potential energy. Am I right? Then, in the water surface $\gamma h \neq 0$ as the pressure but $\gamma h > 0$ as potential energy.