Flip Bucket Problem 1

[SaurabhS]

Hello,

I am trying to figure out the horizontal distance that a water jets out off a steep channel. The channel ends at edge of a cliff. The objective is to determine the horizontal distance the flow will travel before it impacts the ground (which is 16' below).

Basically, the structure involves a steep (s=0.4) 2.5' width rectangular channel which ends in a 2' long horizontal section. A 5.5' radius is applied to the transition. Design flow is 10.6 cfs. I've attached a sketch.

Doing my research, it seems that the 2' long horizontal section may be too short to generate a hydraulic jump. Plus, a hydraulic jump is not desirable.

This may not fit a flip-bucket scenario since there is no bucket lip. (EM 1110-2-1603). The lip is not desirable because of standing water issue.

Is there any method out there that I can use to approximate a solution?

Appreciate the help.
Saurabh

 

[gbam]

Look at a hydraulics text book from college. This is a typical problem that uses velocity and vectors to determine the time and distance. In Hunter-Rouse there is an example in the Berouli's section. I have used this approach to set the distance of Riprap downstream of a drop in an open channel. I will not be in the office next week so I cannot give the formulas; but, the process is rather simple.

 

[Drew08]

It sounds like a basic kinematics problem. Water will go no further than its initial horizontal velocity x the time it takes to fall (t). Where t = (2X/g)^0.5

You can check the velocity lose and potential of a hydraulic jump over the 2' level section by iteratively solving a combination of Bernoulli's and Manning's:

d1 + V1^2/2g = d2 + V2^2/2g + L{Qn/[aAR^(2/3)]}^2

Then, check the froude at the downstream end:
F2 = V2/(gd)^0.5
(if Froude > 1, a hydraulic jump will occur)

AR^(2/3) solved using the average depth (d1+d2)/2

X = Vertical Drop
d = depth
V = Velocity
g = gravity 32.2 ft/sec/sec
L = legth of level section
Q = Flow
n = Manning's
A = Flow Area
R = Hydralic Radius
F = Froude
a = 1.49 (U.S.)