414.  For the most economical trapezoidal open channel,
A. half of the top width must be equal to one of the sloping sides
B. the hydraulic mean depth must be equal to half the depth of flow
C. the semicircle drawn with top width as diameter must touch the three sides of the channel
D. All of these.

---

415. The best side slope for most economical trapezoidal section, is
A. 30?
B. 45?
C. 60?
D. None of these.

---

416.  Tick up the correct statement from the following :
A. For maximum velocity of flow, the depth of water in the circular channel must be 0.81 times the diameter of the channel
B. For maximum velocity, the hydraulic mean depth must be 0.3 times the diameter of circular channel
C. For maximum discharge the depth of flow must be 0.95 times the diameter of circular channel
D. All the above,

---

417.  For critical depth of flow of water in open channels, the specific energy must be :
A. minimum
B. maximum
C. average of maximum and minimum
D. None of these.

---

418. For critical flow, the Froude number is :
A.1
B. less than 1.0
C. more than 1.0
D.2

---

419.  The length of hydraulic jump is roughly
A. 2 to 3 times its height
B. 3 to 5 times its height
C. 5 to 7 times its height
D. None of these.

---

420.  Orifice-meter is used to measure
A. pressure at the point
B. discharge
C. average speed
D. velocity.

---