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Water Resource Engineering Laboratory

The purpose of this thesis is to compile appropriate open channel hydraulic

experiments into a manual for use as a guide for teaching the Water Resources

Engineering Lab at The University of Alabama. Each experiment is presented in a

modular format; therefore, each experiment is completely self sufficient and can be

performed in any order. Each module contains the following sections: Introduction and

Objective, Theory and Background, Experimental Procedure, Experimental Data and

Results, and Discussion of Results. The order in which the modules are covered should

parallel the material taught during the Water Resources Engineering course. The

following is the list of modules that will be covered in this thesis.

• Module 1 - Uniform Flow and its Formulas

• Module 2 - Flow Over a Sharp Crested Weir

• Module 3 - Flow Over a Broad Crested Weir

• Module 4 - Flow Over a Crump Weir

• Module 5 - Flow Under a Sluice Gate

• Module 6 - Critical Depth and Development of Specific Energy Curves

• Module 7 - The Hydraulic Jump

• Module 8 - Flow Profile Reproduction and Computation

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• Module 9 - Flow Through a Culvert

• Module 10 - Flow Over a Dam Spillway

1.2 Instruction Manual Overview

The University of Alabama’s Civil and Environmental Engineering Department has

established a laboratory to house an Armfield Multi Purpose Teaching Flume. This piece of

equipment is used to conduct all of the open channel hydraulic experiments mentioned above.

Each experiment requires the use of different flume accessories that will be explained in each

module.

1.3 Safety

Even though the teaching flume has been designed to ensure safety during operation and

maintenance there are several safety risks that should be brought to the attention of the teaching

assistant and students of the Water Resources Engineering Lab. The first is risk of electric

shock. In order for the flume to operate, the water pump must be connected to an AC power

source. To prevent injury or death from electric shock, any extremity should be kept out of the

flume tank while the apparatus is plugged in and turned on. Also, the pump should be unplugged

whenever the tank needs to be cleaned or refilled. The other major risk of injury is the

possibility of falling due to slippery floor conditions. If the flume overflows or water sloshes

onto the laboratory floor while performing experiments, the flume should immediately be turned

off and any wet spots on the floor should be dried.

1.4 Equipment Operation

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Operation of the teaching flume is extremely simple. To initiate flow in the flume

channel, plug the pump into a wall outlet, press the black button on the flume tank, and open the

flow control valve by turning it counter-clockwise.

Figure 1-1 Flume on/off switch.

Figure 1-2 Flow control valve and flow indicator tube.

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To set the flume at a desired discharge, adjust the flow control valve until the desired

discharge is visible on the flow indicator tube. The units on the tube are displayed in L/s and

divided in tenths of L/s. The discharge displayed on this scale is only an approximation of the

actual flow in the flume. In order to measure exact discharges, the volumetric timing method

should be used. This involves the use of a stop watch to time the volume of water collected in

the upper portion of the flume tank. The first step is to lower the stopper in the upper flume tank.

When the water level reaches the second zero the lower tank level gauge, begin timing. Once the

water level reaches 10.0 L, stop timing. Divide 10.0 L by the time in seconds to calculate the

exact discharge in L/s for a given level on the flow indicator tube. Note: All discharges should

be converted to m3/s before being used in the analysis of experimental data.

Figure 1-3 Stopper in upper flume tank.

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Figure 1-4 Lower tank level for use in the volumetric timing method.

In order to increase the depth of flow in the flow in the flume for certain experiments,

stop blocks may be installed at the downstream end of the channel. There are three sizes of stop

blocks as shown in figure 1-5. Some of the flume accessories do not provide a perfect seal with

the channel walls and bottom. These include the broad-crested weir, culvert, and dam spillway.

To prevent water from flowing around and underneath these structures, Newplast clay may be

installed along their upstream edges during the experiments.

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Figure 1-5 Flume stop blocks, from the bottom: one block, half block, and quarter block.

Figure 1-6 Newplast clay.

1.5 Measuring Depths of Flow

All of the experiments described herein require the use of vernier scales to measure water

depths. There are two identical scales that will be used simultaneously for the majority of the

experiments. These scales are capable of yielding readings to the nearest tenth of a millimeter.

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Unless specified otherwise the datum for all measurements will be the flume bed. This means

that each scale should be zeroed with the tip of the scale touching the bed of the flume. At this

point the zero lines on the left and right side vernier scales should line up and be tightened. To

make a depth measurement, the right side is adjusted until the tip of the scale is slightly touching

the surface of the water. The zero line on the right side is between two whole millimeter

markings on the left side. The lower number is the number to the left of the decimal place. The

number on the right side of the decimal place is number on the right side scale that lines up

perfectly with one of the markings on the left side scale. The pictures below depict a zeroed

scale and a reading of 47.2 mm. Note: all water depths should be converted to meters before

being used in the analysis of experimental data.

Figure 1-7 Vernier scale in zeroed position.

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Figure 1-8 Vernier scale reading of 47.2 mm.

1.6 Measuring Slope

During some experiments the slope of the flume is varied and measured. The slope of the

channel is adjusted by turning the large wheel located at the upstream end of the flume. In order

to establish a level flume bed, place a carpenter’s level across the top of the flume and adjust the

flume height until the bubble in the level is centered. Then measure the height from the

laboratory floor to the bottom edge of the flume structure. This measurement will be referenced

to as the level height. At the beginning of each semester, the level height should be recalibrated

to account for any foundation settlement. (Note: the level height used in the following modules

is 48 5/8 inches.)

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Figure 1-9 Setting the flume slope to zero by measuring the level height.

Any arbitrary slope should be measured using the following steps.

• Increase or decrease the slope as desired using the adjustment wheel.

• Measure the height from the floor to the bottom edge of the flume structure at the

upstream pivot point in inches.

• Subtract 48 5/8 inches from the recorded flume height and divide by the length between

pivot points which is 141 ½ inches.

• The resulting number is the channel slope in inches/inch.

The above information regarding flume operation, measuring depth, and measuring slope have

been discussed in detail in this chapter because they are not discussed in detail with regards to

each module’s experimental procedure. This chapter should be a reference while conducting the

experiments discussed in each module.