· Closed-toed shoes are required in the Hydrotechnical Lab
· Safety glasses are required in the Hydrotechnical Lab
· Incorrect use of the apparatus may cause water hammer which may burst the pipes
· Never leave power connections (eg electrical plugs) on the ground in case of flooding
Measure the flow rate
The following videos demonstrate how to measure the water flow rate. There are two different methods shown in each video so please watch both of them.
Estimating water flow video
Follow these steps to complete the lab and refer to videos when needed
1. Check the reservoir to ensure it has enough water. Approximately one foot below the top of the reservoir.
2. Slide seven plastic slides into the slot in the middle of the flume for the variable height weir. Be careful to slide them in perpendicular to the flume wall as they will stick.
3. Check that the outlet valve of the pump is closed and turn on the pump.
4. Open the outlet valve to set the depth upstream of the weir to 30cm (3 or 4 ticks on the valve).
5. Set the height of the downstream weir so the hydraulic jump is located between the ends of the wooden ruler.
6. The velocity probe is located in the white abs tube and the counter is in the gray equipment cabinet in a plastic yellow protective box. Take one of the propellers out from the box and assemble on to the end of the probe.
7. Turn on the power by holding down the PWR button. Press VELOCITY to set the probe to measure velocity.
8. The two rods on the probe slide apart. Plant the probe on the bottom of the flume upstream of the weir and measure the fluid velocity at 10%, 40% and 80% of water height. Keep one rod on the touching the bottom of the flume for stability. Press ENTER to begin measuring. Place the probe anti parallel to the flow and maintain enough space between probe and the weir to avoid the dead zone created by installment of the weirs.
9. When you are done with the velocity probe hold down PWR to turn off the device.
10. Time how long it takes to fill the small graduated cylinder from the Mariotte’s bottle to measure the flow rate. Repeat the measurement two or three times to improve accuracy. If the Mariotte bottle is less than ½ full , then add water till full then add salt and mix until conductivity meter reads approximately 15 milliSeimens ( start by adding about ¼ cup of salt and mixing by putting lid on and shaking).
11. Get the conductivity meter (from grey cabinet) and push the power button to turn on then push the 20 mS (milliSiemens) range. The reading in the flume should be below 0.5 milliSiemens. With one person downstream holding the conductivity meter in the water falling from the flume. Have another person open the spigot on the Mariotte’s bottle. Keep open for 30 seconds and time how long it takes for the conductivity to spike. Repeat this measurement twice to improve accuracy.
· The spike will peak quickly and then the reading slowly drift up as the background conductivity in the flume increases. Be sure to use the first spike for the timing
Hydraulic Jump Characteristics
12. Ensure that the hydraulic jump is located between the two ends of the wooden ruler.
13. Measure the depth upstream of the weir. Measure depth of the supercritical flow section downstream of the weir, upstream of the hydraulic jump. Measure the water depth downstream of the hydraulic jump.
1. Add the 2 remaining plastic slides to the weir.
2. Make sure the hydraulic jump is positioned a distance away from the weir, preferably between the two ends of the wooden ruler.
3. Measure the height of the weir.
4. Measure the depth slightly upstream of the weir.
5. Measure the depth slightly downstream of the weir.
6. Measure the depth at the crest of the weir.
7. Remove one plastic slide from the weir.
8. Repeat steps 3 – 7 until you have data for 7 different weir heights.
Bridge footing constrictions
9. Remove all the slides for the variable height weir.
· There are three sets of plates. Two thin sets and one thick set.
· Place a thin, and wider plastic plate on each side of the flume. Hold the plates in place with the thumb screw attached to the crossbar.
10. Wait for flow to stabilize and measure the depth upstream of the plates.
11. Measure depth between the plates.
12. Measure depth downstream of the plates. Ensure that you are measuring upstream of the hydraulic jump. If you need you may lower the weir to remove he hydraulic jump.
13. Repeat steps 9 – 12 for the following plate configurations, thick-thin-water-thin-thick and thin-water-thin.
· For the stacked plate setup ensure that the transition is smooth by aligning the bevels on the plastic plate.
14. Remove the plates and replace them where you found them