Sacramento State University	Dept. of Civil Engineering
	CE 135 Hydraulics Lab	Instuctor      MEH

FLOW OVER A SHARP-CREASTED WEIR

To examine the fundamental characteristics of flow over two sharp-crested weirs
To determine the coefficients of discharge of the rectangular and triangular weirs
To examine the pressure forces on and around the rectangular weir

Half-meter flume and sharp-crested weir with manometer taps
V-notch weir in return-flow channel
Point gages and manometer board

Set up for the experiment.
Open the surge tank valve and turn on the large pump.
Close the drain valve on the upstream side of the flume head tank. br>Leave the gate at the downstream end of flume open for the entire lab.

Open the feed valve until water overflows the V-notch weir
Close the feed valve (There should be a small water level covering all the taps along the flume)

Record the Constant Data items
The piezometers should read constant values at the same level as the water in the flume (constant levels before & after the weir)
If needed, add water to force the upstream static water level to the height of the weir.
Use the point gages to measure the elevations at the rectangular crest height and the vertex of the V-notch.

Calibrate the Rectangular and V-notch Weirs
For a series of flows (up to about 600 or 700 gpm):
• Establish a steady flow and record the discharge
• Also record the water levels (heads) at both weirs


[Note: Storage of water in the channel may cause the V-notch weir head to stabilize slowly, so don’t change the flow rate prematurely]
Draw a sketch showing all points where you took data

Forces On Rectangular Weir: Data Collection
Establish the flow over the weir crest necessary to obtain a head of about 0.3-ft
• Make sure the air vent is open

Record flow rate from the flow meter
Record the height of the piezometers at tap 1 & taps A-F
• Taps A-F record the pressure on the face of the weir; the numbered taps record the pressure on the bottom of the flume

Record the point gage reading at tap 1

Close the valve on the ventilation pipe at the base of the weir
• Note the change in the nappe profile and level of water backed up against the downstream face of the weir.

Sketch the vented & unvented patterns.

Surface Profile Along Flume
Set the flow to 600-700 gpm.

Record the manometer and point gage readings for positions 1-14.

• For the area just after the weir, record both water levels with the point gage
• Make sure the air vent is open for these measurements
Sketch the equipment used to get data

Close the flume feed valve, open the drain valve on the head tank and turn off the pump.

FLOW OVER A SHARP-CRESTED WEIR -- RESULTS

Present the key results and describe any major deviations from the printed procedures and why you did them. Report flows in cfs, head in ft, & time in seconds.

You do not need to turn in the lab procedure sheet with your report, but it is ok to add it as an attachment.
You may use a computer sketch of the apparatus in the body of the report, but the attachment must be hand drawn.

RESULTS:

Plot the approaching head and flow data for the vented rectangular weir, and the V-notch weir on a graph with log-log-scaled paper.
Determine the unconstrained equations of the rating curve for each device.
Comment on the linearity of your plotted rating curves (e.g. standard deviation and coefficient of determination)

Compare your experimental values for the vented rectangular weir and the V-notch weir with literature equations or graphs such as the equations in Ch. 13 of Roberson & Crowe.
• Are the values of the exponent on the approaching head and the weir coefficient consistent with theory and empirical relations in the literature?
• Using an exponent of 1.5 for the heads on the rectangular weir and 2.5 on the V-notch weir, compute the weir coefficients for both weirs at each experimental flow rate. Is the use of constants for the exponent and the coefficient acceptable?
• Compare the performance of the V-notch weir with that of the rectangular weir at both high and low flows.

Plot the pressure distribution curve from your manometer data on the upstream face of the rectangular sharp-crested weir.
Calculate the force on the weir by integration of the pressure distribution and compare this value with that obtained by assuming a linear hydrostatic pressure distribution.

For the convenience of computation, the hydrostatic assumption has been widely used by the engineers. Do you think the assumption is acceptable in terms of accuracy and magnitude? Overestimated or underestimated

How do your sketches of the water surface profiles for the vented and unvented conditions of the rectangular weir compare?

OPTIONAL EXTRA CREDIT ITEM
Plot the surface profiles from the manometer and point gage data collected for taps 1-14
How closely do the two profiles match?
Which method do you consider is better to use?

Attach your sketches of the experimental set-up and copies of your input data and calculated results.
Write out the key equations used in calculating the results, with one sample calculation for each equation.

References:

Roberson, J.A. and C. T. Crowe, Engineering Fluid Mechanics, 6th ed., John Wiley and Sons, 1997, pp. 542-546
Daugherty, R., J. Franzini, and E. J. Finnemore, Fluid Mechanics with Engineering Applications, 8^th ed., McGraw-Hill, Inc., 1985.

	Sacramento State University	Dept. of Civil Engineering
	CE 135 Hydraulics Lab	Instuctor      MEH

WEIR CALIBRATION: EXPERIMENTAL DATA

      Lab Team Members:                                            Date of Experiment:

Observe shapes for flows over the two weirs at a high flow rate. Sketch the patterns. Note the conditions near the rectangular weir for both vented and non-vented flows.

FLOW PROFILE WITH SHARP-CRESTED WEIR: INPUT (OBSERVED) DATA