§ 41. _Notches, Weirs and Byewashes._--A notch is an orifice extending
up to the free surface level in the reservoir from which the discharge
takes place. A weir is a structure over which the water flows, the
discharge being in the same conditions as for a notch. The formula of
discharge for an orifice of this kind is ordinarily deduced by putting
H1 = 0 in the formula for the corresponding orifice, obtained as in
the preceding section. Thus for a rectangular notch, put H1 = 0 in
(8). Then