7/29/2019 broad crested weir lab.docx

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Hydraulics Lab: Broad Crested Weir

Objective:

To determine the relationship between upstream head and flow-rate for water flowing over a

broad crested weir, to calculate the discharge coefficient and to observe the flow patternsobtained.

Procedure:

Ensure the flume is level and measure/record width of flume

Place weir in the flume with the rounded corners facing upstream. Secure the weir to the flume

and seal the sides to prevent water passing on the sides.

Carefully adjust the level gauges to coincide with the bed of the flume and record the readings

from the datum. Measure the height of the height of the weir above the flume bed. Position thegauge over the weir at the discharge end and measure the height.

Adjust the flow of water through the flume to obtain heads that are increasing at 1in steps. For

each step, measure the flow rate Q, the upstream depth of flow Yo, and the depth of flow over

the weir Yc.

Results and conclusion:

Plot graphs of Q against H, Log Q versus Log H, and Cd versus H

From the straight line graph of log Q against log H, find the intercept log k on the log Q axis and

the gradient m.

The relationship between Q and H is then Q = kH^m where k=1.705*Cd*Cv*b