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close this bookA Training Manual in Conducting a Workshop in the Design, Construction, Operation, Maintenance and Repair of Hydrams (Peace Corps, 1981, 216 p.)
close this folderSession 3: Water measurement techniques (3 hours)
View the document(introduction...)
View the documentHandout 3A: Using a Weir
View the documentHandout 3B: Using a Weir - diagram
View the documentHandout 3C: Weir table
View the documentHandout 3C: Weir table - metric
View the documentHandout 3D: The float method of measurement

(introduction...)

Total Time: 3 hours

OBJECTIVE:

By the end of the session, the trainees will be able to accurately measure the flow rate of moving bodies of water using a weir, a bucket and watch, or the float method.

OVERVIEW:

It is important during this session that the trainees gain experience in estimating flow rates and develop skills in measuring flow rates. Three methods of measurement shall be presented: 1) the weir method, 2) the bucket and stop watch method, and 3) the float method. Each method will entail "hands on" work, constructing a weir, channeling the stream, placing stakes in the stream, etc. The findings from these three methods will be compared.

MATERIALS:

Handouts 3A - 3D


lumber, nails, approximately 3' of pipe with a sufficient diameter for the expected flow, sheet metal (optional), bottle with cork, or float. Have a set of materials for each team.

TOOLS:

watch with a seconds function, bucket of known capacity, saw, level, tape measure, hammer, pick or mattock, tin snips (optional), have one set of tools for each team.

*TRAINERS NOTE:

1)Since the purpose of the activity is to learn to measure, not build, pre-construction of site levels, weirs is recommended.


2) The weir table is provided in both English and metric units;


3) the float method has limited applicability. Decide whether or not to spend time conducting the field activity.


4) Identity site for field activity ahead of time, ensuring enough locations for small groups or pairs to work independently; stake out distances if necessary.


PROCEDURES

NOTES

1.

Discuss the need for water measurement in hydram systems:



- amount of water delivered



- amount of water into ram


2.

State objectives for the session.


3.

Ask participants to approximate amount of water needed for:



irrigating an average garden



domestic use



potable water


4.

For each, ask participants to compute amount of water needed to enter the ram given H=10', h=30'.

This problem links and review Session 2.

5.

Distribute the handouts and make a transition to the task of measuring water available.


6.

Describe the weir and what it is used for.


7.

Describe how to build and install a weir.

A desk top model would work well for this and could substitute for the real exercise if time and facilities aren't available.

8.

Explain how to use the weir table.


9.

Go over the example in the handout and make certain everyone feels comfortable with their ability to use the weir table.


10.

Describe how to use the bucket and watch method.

Use discretion as to how much detail to go into as this method is used on flows that would be considered infinite with a ram installation. (float method)

11.

Describe the float method of measurement .


12.

Explain steps in determining cross-sectional area of a stream.


13.

Explain procedures in determining the velocity of the stream.



PROCEDURES NOTES


14.

Go over the example in the handout.


15.

With the trainees, go over the sequence of events involved in the remainder of this session and how much time is left.


16.

Divide the trainees into groups of three or four, giving each group an even level of total skills.


17.

Proceed to the creek or stream.


18.

Locate a section along the creek or stream where the flow is consistent and there is sufficient room for all the groups to work within sight of each other.


19.

Have each group select a site which they feel will be easily developed.


20.

Have each trainee make--a guess as to flow rate of the creek or stream they are measuring.


21.

Note estimates of flow rate.


22.

Calculate flow rate by the float method

Use only if time allows and the water source is appropriate.

23.

Select appropriate section of the stream or creek and determine cross-sectional area.


24.

Place two stakes in stream at appropriate spots and distance from each other.


25.

Place float in mid-stream and measure time it takes for float to travel from one stake to another.


26.

Repeat measurement several times and average the flow rate.


27.

Note differences between original estimates and measurements of flow rates.


28.

From the measurements made, have each group decide on the size of their weir notch.


29.

The trainees next construct their weirs and install them in the creek, making certain that the weirs are well supported and sealed against leakage around the bottom and sides.

It may be a good idea to have each group build their weir out of different materials so that the construction techniques can be compared.

30.

After the weirs are constructed, readings should be taken periodically while the water is seeking its new level and while flow rates are being interrupted by the other weir installations. Once the readings become consistent, they should be considered reliable.


31.

Using the weirs as partial dams, in stall the short lengths of pipe and seal around them in the same manner that the weirs were sealed.


32.

With all the water flowing through the pipe and into the bucket, time how long it takes to fill the bucket. Again readings should not be considered reliable until they are consistent.


33.

At this point, review what has been done thus far in the session.


34.

Back at the classroom, list the readings from each group and discuss the reasons for the variations. If different materials were used for the weirs, discuss the advantages and disadvantages of each.-

Point out need to measure seasonal variations of water flow

35.

Ask participants which method they would use, given resources at their site.