M1Q8

Which of these actions would make a hydraulic jump taller (increase the difference between upstream and downstream depths)?

Question

M1Q8

Which of these actions would make a hydraulic jump taller (increase the difference between upstream and downstream depths)?

BlackTom AI · Accepted Answer

Question restatement: M1Q8 asks which action would make a hydraulic jump taller, i.e., increase the difference between upstream and downstream depths. Answer options: 1) Increase roughness after the jump, 2) Decrease roughness before the jump, 3) Force the flow to reach critical depth before the jump, 4) Install a sluice gate.

Option 1: Increase roughness after the jump. Conceptually, roughness after the jump adds energy losses in the downstream reach. While this can lower downstream flow depth by dissipating more energy, it does not inherently increase the height of the jump—the jump height is set by upstream conditions and the transition from supercritical to subcritical flow. In many cases, greater downstream losses tend to reduce the apparent depth difference across the jump, or at least do not promote a taller jump. So this choice is not the most effective way to taller the jump.

Option 2: Decrease roughness before the jump. Reducing upstream friction would change the energy budget: less head loss upstream could increase the upstream velocity or depth depending on the channel, potentially altering the Froude number at the jump. However, simply reducing roughness upstream does not guarantee a larger depth difference across the jump; the jump height is not controlled solely by upstream roughness, making this option unlikely to reliably yield a taller jump.

Option 3: Force the flow to reach critical depth before the jump. Reaching critical depth before encountering the jump changes the hydraulic state that the jump must accommodate. When flow arrives at the jump already at critical depth, the downstream adjustment (the jump) can be forced to occur with a larger depth difference between the upstream and downstream sides, effectively increasing the jump height. This aligns with the understanding that the jump adjusts to satisfy conservation laws given upstream depth and flow regime; altering the upstream state to critical depth tends to produce a taller jump.

Option 4: Install a sluice gate. Placing a gate can back up the flow and modify upstream depth, but it introduces a controlled constraint that may either reduce the jump height or produce a different regime, depending on the gate position and operation. It is not a straightforward method to guarantee a taller jump, and in many configurations could even suppress or relocate the jump rather than heighten it.

Summary of incorrect options: The first two options rely on frictional changes in the downstream or upstream reach but do not reliably increase the depth difference across the jump. The fourth option changes boundary conditions with a gate, which may produce various effects but does not consistently heighten the jump. The third option directly manipulates the upstream hydraulic state to critical depth, which.

leads to a larger required downstream adjustment and a taller jump. In typical open-channel hydraulics reasoning, forcing the flow to be at or near critical depth upstream tends to increase the jump height when a transition to subcritical flow must occur downstream.

Final note: The explanation above describes why each option could or could not influence the jump height, focusing on the relation between upstream state, energy losses, and the jump’s role in reconciling conservation laws across a supercritical-to-subcritical transition.

CVEN90051_2025_SM2 Exam: Civil Hydraulics (CVEN90051_2025_SM2)- Requires Respondus LockDown Browser

M1Q8 Which of these actions would make a hydraulic jump taller (increase the difference between upstream and downstream depths)?

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