For designing the venturi head,

• width of the throat should not be less than one-third of the bed width of main canal
• width of the throat should not be less than the width obtained from the formula B = Q / 1.2d3/2, where d is the difference in levels of F.S.L. and sill
• minimum throat width should not be less than 60 cm
• length of the throat should be 2.5 times the depth measured to F.S.L. in the main canal
• all the above.