 It is the type of V. F. in which the width of throat is decreased to such an extent that the depth of water in throat is equal to critical depth.  The velocity of flow through the throat corresponding to critical depth is also critical.  Therefore the existence of critical conditions of flow in throat will cause a standing wave on the d/s of V.F.  such a V.F. which causes a standing wave on its d/s and have critical condition in its throat is known as modular V.F. or standing wave V.F.

 Specific energy at 1-1  Specific energy at 2-2

 Now neglecting loss of energy in gradually converging portion of the flume Then

Or Theoretical discharge through the venturiflume is

 As depth of water at throat is critical so discharge at critical depth is maximum.  In eq (4), Q will be maximum when the factor is maximum as all other parameters are constant

Differentiating wrt h 2 and equating to zero

Substituting in eq (3)

 C = coeff of V.F. depending on smoothness of surface of bed/sides and roundness of corners of V.F. and its value lies between

 A discharge of 1000(litre/sec) flows along a rectangular channel 1.5m wide (a) what is critical depth in the channel (b) if H.J. is to be formed at a point where u/s depth is 180mm, what is height of H.J.  A rectangular channel 6m wide discharges 1200(l/s) of water into 6m wide apron with a velocity of 6m/s. What is height of H.J. how much energy is absorbed in the jump

 A broad crested weir 10m long has maximum discharge 10,000 (l/s) determine the head of water on u/s side of the weir for this discharge, if coef of discharge is  Determine the maximum discharge over a broad crested weir 60m long having 60cm height of water above the crest of weir. Coefficient of discharge is also determine the new discharge over the weir considering velocity of approach, the channel on the u/s of the weir has a cross sectional area 45m 2

 A rectangular channel 2.4m wide is provided with venturiflume of 1.5m wide throat. Find quantity of water flowing through the V.F. when depth of water into u/s side 1.2m and at throat is 0.9m.  A modular V.F. has an approach channel 3m wide having throat of 1.5m width. Calculate discharge when u/s depth is 1m. Take C = 0.95