# Civil Engineering - UPSC Civil Service Exam Questions - Discussion

12.

The discharge per metre width at the foot of a spillway is 10 m3/s at a velocity of 20 m/s. A perfect free hydraulic jump will occur at the foot of the spillway when the tail water depth is approximately equal to

 [A]. 4.50 m [B]. 5.00 m [C]. 5.50 m [D]. 6.50 m

Explanation:

No answer description available for this question.

 Danesh said: (Sep 24, 2013) V*Y = q. From here y1 = 0.5. Now, y2 = (y1/2)*((sq rt of 1+8F^2)-1).

 Abhay said: (Feb 3, 2016) Discharge Q = Velocity * Head (or water depth). Q = 10 m^3/s. v = 20 m/s. h1 = 10/20 = 0.5 m. The jump will occur if and only if the level of inflowing (supercritical) water level (h_0) satisfies the condition: h0/h1 = [-1 + √(1 + 8v^2/(9.81 * h1))]/2. h0/0.5 = [-1 + √(1 + 8*20^2/(9.81*0.5))]/2 = 3.32. h0 = 6.64 m.

 Mohsin said: (Apr 5, 2018) @All. Discharge = velocity x area. area= width x height. In question discharge per meter width is given as 10 cms, therefore, Unit width discharge = velocity x height.