Task: 1 Discharge Measurement using floating method
Equipment’s Required
Meter
Floating Material
Stopwatch
Note book +Pen
Peg
Procedures of floating method
1. Measuring of width or average width of an open channel
In order to measure the width of a channel the following procedures should be followed:
(1) Select marks on the string to indicate the exact water surface on both sides of the channel;
(2) Then measure the distance between the two marks and this is the width of the channel.
2) Measuring the average depth of water
In order to measure the average depth of water it is possible to use bamboo or a piece of
wood circular at the base.
The wooden piece should have a thickness of 3- 8 cm in order to resist the pressure of the
water and delineated on it in meter and centimeter.
The measuring can be done on the same area where the width is measured and
measurements are taken at 30 cm interval.
The average depth can be determined by dividing the sum of all the measured depths by
the number of measurements taken
Sample data for measuring depth:
Number of tests 1 2 2 4 Average
Depth, m
(3) Measuring the cross- sectional area
The cross- sectional area is calculated by multiplying the width by the average depth of
the canal.
To do this first it is recommended summing up of all the partitions subdivided to measure
the depths at certain intervals and then multiply the result with the average depth.
Cross- sectional area, m2 = average width, m x average depth, m
(4) Measuring of the water velocity in an open channel
In order to measure the velocity of water the following procedures should be followed:
Using the tape measure or mark out a 10 m run along the bank of the ditch /water
channel/ demarcating the beginning and the end of the length using the two wooden pegs,
the strip should be parallel to the flowing of water;
Mark out a point on the upstream side of the channel at 5 m distance where width
measurement is taken and name the section A- A and place peg 1;
Stretch another string on the downstream side at 5 m distance from the upstream point
and mark peg 2 and name the section B- B;
Then stretch a third string about 10 m away from the second peg to the downstream side
and mark peg 3 and name the section C- C;
The water velocity in the channel could be measured using a floating object;
The floating object could be any other floating object like a tennis table ball;
Put the floating object on the upstream side at 5 m from the second peg at a section A- A
and check whether the floating object is floating or not;
Place the floating object in the middle of the water flow just at section A- A and note the
first time reading when the float is passing the second peg and record the time when the
object passes the second peg and calculate the total time taken from section B- B and C-
C;
Repeat the test at least three to five times and record the times all the time in order to be
more accurate in estimating and obtained an average velocity.
Dividing the distance from section B- B to section C- C by the time taken for the float
object to pass from section B- B and A- A gives the actual speed of the water; Average
speed of water, m/s is equal to distance from section B- B to section C- C (m) divided by
the average time taken by the float object (s).
Finally, knowing the cross- sectional area of the channel and the average velocity of the
water in the channel, the discharge of the water in the open channel
Test No. Length, m Time (Sec) Velocity, m/s
1
2
3
4
Average
