LAB 3 Surface Profiles

 

Safety Considerations
System Setup
Video: Setup for shallow water waves
Non-uniform channel profiles

 

Introduction

Safety Considerations

 

  • Closed toed shoes are required in the Hydrotechnical Lab
  • Safety glasses are required in the Hydrotechnical lab
  • Never leave power connections (e.g. electrical plugs) on the ground in 
case of flooding
  • Do not touch the pump drive shaft
  • Operate the jacks slowly, adjusting the elevation of the flume too quickly can damage the flume

System Setup


The system is a recirculating flume with its own pump. Water flows from the pump through the flume before returning to the sump. The slopes of the upstream and downstream sections can be set independently because of the hinge point. Two separate jacks exist, one for adjusting the upstream slope and the other for adjusting the downstream slope. The upstream sluice gate and downstream weir are both adjustable.
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Procedure

 

Shallow Water Waves

Video: Setup for shallow water waves


 

  1. Check the reservoir, it should be more than half full. Use the water hose on the north wall to fill the reservoir if needed.
  2. Locate the digital level. It is stored in the nearest gray equipment cabinet.

digital level
Figure 1. Digital level

    1. Make sure the pump outlet valve is closed (red handle). Close the weir at the end of the channel and the gate at the upstream end. Turn on the pump.
Weir at Channel's End

Weir at Channel’s End

 

    1. Set the flume to a gradient of 0.0% on both the upstream and downstream sections by adjusting the hydraulic jack.Note: Raise the jack by using a lever to pump the jack. Lower the jack by rotating the screw on the bottom of the jack to release pressure. If there is not enough weight on the jack, push down gently on the flume while rotating the screw.
    2. Rotate the pump outlet valve to release water and fill the box to the fourth screw, then close the valve.
Pump Valve Releases Water

Pump Valve Releases Water

  1. Quickly lift up the upstream weir and release the water pulse.
  2. In a few seconds when the water level reaches a local minima, close the upstream weir again so the wave will reflect off of it.
  3. After several reflections have occurred, the disturbance will resemble a series of low amplitude waves. These represent shallow water waves.
  4. Measure the wave speed by timing the wave as it moves through the flume over a distance (e.g. 10 ft.).
  5. Measure the water depth in the flume. Measure the water depth in 3 different locations (approximately 2, 4 and 6 cm) and take an average.
  6. Without opening the downstream weir, keeping all the water in the flume, repeat steps 5-8 twice more to measure the wave speed at different depth.
  7. Drain the channel by opening the downstream weir.


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Non-uniform channel profiles

Mild slope 0.5% gradient

    1. Set the gradient of the flume to 0.5%. This requires two people. One person measures the slope from the middle of each flume section. The other operates the hydraulic jack. Raise the upstream section and lower the downstream section.
Hydraulic Jack

Hydraulic Jack

  1. Open the valve to a reasonable flow rate (~4 on the dial) and record the number shown on the valve. The flow rate should be kept constant throughout the rest of the experiment.
  2. Adjust the downstream weir and upstream sluice gate to achieve approximately non-uniform flow. There is a screw on the underside of the flume to hold the weir in place.
  3. Measure the flow rate by timing how long it takes to fill a bucket of known volume. Repeat this measurement three times and take an average. Keep the flow rate constant throughout the experiment to avoid needing to repeat the flow rate measurement.
  4. Measure the water depth along the flume and sketch the surface profile.
  5. Determine and record the type of flow seen in the channel.
  6. Measure the average velocity of the flow by timing the plastic pellets in the flume as they flow downstream.
  7. Splash the water surface and determine if the wave can propagate upstream.

Steep slope 2% gradient
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  1. Raise the upstream jack to get 2% gradient on the upstream section.
  2. Lower the downstream jack to get 2% gradient on the downstream section.
  3. Adjust the downstream weir to see how it affects the flow (creates a hydraulic jump). Then remove the downstream weir.
  4. Adjust the upstream sluice gate to achieve non-uniform flow.
  5. Measure the water depth along the flume and sketch the surface profile.
  6. Determine and record the type of flow seen in the channel.
  7. Measure the average velocity of the flow by timing the plastic pieces in the flume as they flow downstream.
  8. Splash the water surface and determine if the wave can propagate upstream. If the wave cannot propagate upstream it is supercritical flow. If the wave can propagate upstream the flow is subcritical.

Mild to Steep flow
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  1. Lower the upstream jack to get a gradient of 0.5% on the upstream channel.
  2. Measure the water depth along the flume and sketch the surface profile.
  3. Determine and record the type of flow seen in the channel.
  4. Splash the water surface and determine if the wave can propagate upstream.

Steep to Mild flow

  1. Raise the upstream jack to 2% for supercritical flow
  2. Raise the downstream jack to 0.5% for subcritical flow. May need to insert the downstream weir from below and secure with the screw to induce downstream flow. Should be able to see a hydraulic jump.
  3. Measure the water depth along the flume and sketch the surface profile.
  4. Determine and record the type of flow seen in the channel.
  5. Splash the water surface and determine if the wave can propagate upstream.