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EXPT.No.7-C 1

HYDHYDRAULICS LABORATORY

Experiment No.7-CDetermination of the Coefficient of Discharge

over a Triangular Weir

Triangular or V-notch weirs are the most accurate open channel constrictions formeasuring discharge. The discharge of a V-notch weir increases more rapidly with thehead than in the case of a horizontal crested weir (rectangular or trapezoidal), so for thesame maximum capacity, it can measure much smaller discharges, compared to arectangular weir.

The general equation to compute the theoretical discharge in a v-notch weir includingeffect of approach;

()

where: - interior angle of the weirH - head over the weirQ - discharge

To calculate the actual discharge we introduce a coefficient of discharge, Cd, which

accounts for losses at the edges of the weir and contractions in the area of flow, giving:

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EXPT.No.7-C 2

HYDHYDRAULICS LABORATORY

I. Experiment Objectives

- To observed the characteristics of open-channel flow over a triangular weir.- To determine value of the discharge coefficient for triangular weir.

II. Materials and Apparatuses Required

The apparatuses necessary to perform this experiment are the following:

- Tilting Flume Apparatus- Calibrated Bucket- Stopwatch- Metric Scale- Triangular Weir

III. Procedures

a) Attach the triangular weir to the channel (Flume).b) Measure the interior angle of the triangular weir.c) Turn on the pump and open the control valve until water discharges over the

weir.d) Regulate the flow to maintain a water level in the flow channel so that the weir is

filled to the highest possible level without overflowing the channel.e) Allow a steady flow to develop throughout the entire circuit.f) Measure the height of the water level above the top of the weir as an H to start

the analysis.g) Measure the flow rate with a stopwatch and calibrated bucket.h) For each set of measurements, measure the flow rate at least three times and

take the average.i) Reduce the approach, repeat step e to step h by using different flow rate of

water, which can be done by adjusting the water supply. Measure and record theH and the time to fill a certain volume of water in the bucket.

j) Compute for the theoretical discharge using the equation;

()

k) Calculate the actual discharge by volumetric method using the formula;

l) Determine the coefficient of discharge of a v-notch weir:

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EXPT.No.7-C 3

HYDHYDRAULICS LABORATORY

IV. Laboratory Data

TRIAL

ACTUAL DISCHARGE THEORETICAL DISCHARGECOEFFICIENT OF

DISCHARGEVOLUME

(m3)

TIME

(sec)Qa H (m) Qt Cd Cd (AVERAGE)

1

2

3

COEFFICIENT OF DISCHARGE, Cd

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EXPT.No.7-C 4

HYDHYDRAULICS LABORATORY

V. Observations

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VI. Conclusions

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