Investigation was carried out to study the characteristic of flow over four model of orifice

measuring structure in a concrete lined rectangular open channel in the irrigation laboratory of

the department of agricultural and bio-resource engineering Ahmadu Bello university Zaria

Kaduna. The four physical orifice mode (with a pipe at angle 60, 45 degree and without pipe at

theoutlet andwith zeropipeweredesignedwith steel metal plate) usedfor thestudy, thedischarge

from

thewater pumped machinethrough theopen channel wasdetermineusing direct method and

used to determine the coefficient of discharge (C d ) for each of the measuring structure. The C d

obtains for the orifice structure with pipe at angle 60, 45, and with no pipe at the outlet and with

zero pipeswas found to be 0.99, 0.085, 2.755 and 1.122 respectively. The mathematical function

for the head discharge for the orifice with pipe at angle 60, 45, and with no pipe at the outlet and

with zero pipes were found to be;