The figure below shows a lab experiment to demonstrate an open channel flow. It is given that h $=0\mathrm{.}07$ m$,$ b $=0\mathrm{.}4$ m$,$ L $=1\mathrm{.}8$ m$,$ and d $=0\mathrm{.}2$ m$.$ If the fluid flow rate in the experiment is $40$ l$/$s$,$ Calculate

Manning$$s constant $($n$)$

b$=$ the base of channel cross section

d$=$ height lf cross section channel

L$=$length of the section of the channel

h $=$height between the start and end of the length