This document discusses various techniques for measuring stream flow, which is the volume of water moving through a designated point over time. It describes common methods like the velocity-area method, using a weir, and the bucket method. It also outlines different types of meters that can directly measure flow properties like velocity, including pygmy meters, vortex meters, and current meters. Accurately measuring stream flow is important for applications like flood prediction, assessing water and sediment levels over time, and monitoring long-term climate changes. A combination of techniques may be needed to account for variability in flow across seasons.

1. NED UNIVERSITY OF ENGINEERING AND TECHNOLOGY
STREAM FLOW
MEASUREMENT
TECHNIQUES
URBAN HYDROLOGY AND MUNICIPAL ENGINEERING

2. TABLE OF CONTENTS
1. STREAMFLOW.......................................................................................................................................3
2. IMPORTANCE OF STREAMFLOW MEASUREMENT.................................................................................... 3
3. STREAMFLOW MEASUREMENT METHODS.............................................................................................. 3
4. VELOCITY-AREA METHOD (FLOAT-METHOD)........................................................................................... 4
4.1 Equipment Needed........................................................................................................................... 4
5. MEASURING DISCHARGE USING A WEIR ....................................................................................... 5
6. BUCKET METHOD...................................................................................................................................6
7. METERS .............................................................................................................................................. 7
7.1 PYGMY METER .................................................................................................................................7
7.2 Vortex meter....................................................................................................................................7
7.3 Current meter..................................................................................................................................7

3. 1. STREAM FLOW
Stream flow, or discharge, is the volume of water that moves over a designated point over a fixed
period of time. It is often expressed as cubic feet per second (ft3/sec).
The flow of a stream is directly related to the amount of water moving off the watershed into the
stream channel. It is affected by weather, increasing during rainstorms and decreasing during dry
periods. It also changes during different seasons of the year, decreasing during the summer months
when evaporation rates are high and shoreline vegetation is actively growing and removing water
from the ground.
2. IMPORTANCEOF STREAMFLOWMEASUREMENT
Streamflow is of fundamental importance to virtually all environmental monitoring and affects almost
all other environmental issues connected with water. The flow of rivers changes significantly in a
very short amount of time due to plenty of factors. Snowmelt from mountainous regions has a major
impact on rivers and can cause them to swell past their banks really quickly. Ice flows are also
hazardous, especially when the temperature soars after having been below freezing for a long time.
Thunderstorms also produce torrential downpours which results in flash flooding in many places.
This is even more of a hazard because it can significantly increase the water levels in a small river or
stream in a matter of minutes.
Streamflow measurements can yield information on changes in discharge that are valuable for
predicting flooding, estimating long-term trends in water and sediment discharges, and for
distinguishing possible long-term climate change.
3. STREAM FLOWMEASUREMENTMETHODS
It is important to measure the stream flow as it assess the quantity of water that is available and also
to check the quantity of water that is flowing through the treatment plants or system.
There are several techniques available for the measurement of flow of rivers and stream. Often all
that is feasible to make an initiative assessment of flow as a part of the selection of water sources.
This indicates that only a limited number of flow measurements can be taken. Now these limited
numbers of measurements create a risk of not determining the appropriate measurement of the stream
flow because there are variations in stream flow during different seasons. So due to this reason it is
important to get information from the local community to get familiar with the high and low water
flows and level that may be seen during the measurements.

4. The methods that are used widely for the measurement of flow on surface are as follows:
4. VELOCITY-AREAMETHOD (FLOAT-METHOD)
The velocity area method is a technique used to investigate the stage and discharge of a river. The
discharge of a river is the volume of water which flows through a cross-section in a given time. It is
measured in m3/s. Stream flow is affected by a number of factors including rainfall, temperature and
snow melt. Measuring the discharge is important because first and foremost it is crucial in predicting
floods. In addition the velocity and flow of a river affects food sources and the migration of fish
amongst other wildlife.
4.1 EquipmentNeeded
 Tape Measure
 Waders
 Flow meter
 Pencil and notepad
In order to calculate flow of stream , it is important to first calculate the stream velocity using flow
meter. It is also important to find out the cross section of the stream graphically. The simplest way to
measure discharge is to divide the channel cross section into vertical rectangular subsections. Once
the area (width X depth) of each of these subsections is established and multiplied by velocity to
determine subsection discharge, the results can be added together to calculate total discharge.
Discharge=Velocity x Cross sectional area
Or
Discharge = (Water velocity) x ((Width) x (Depth))
Where
Discharge = Q (
𝑚3
𝑠𝑒𝑐𝑜𝑛𝑑
) 𝑜𝑟 (
𝑓𝑡 𝑒
𝑠𝑒𝑐𝑜𝑛𝑑
)
Velocity = Meter/second or feet/second
Cross-sectional Area= Cubic meter or cubic feet

5. 5. MEASURING DISCHARGE USING A WEIR
Weirs are overflow structures built across open channels to measure Suppressed rectangular weir the
volumetric rate of water flow. Discharge in small streams can be conveniently measured using a weir.
A weir is a small dam with a spillway, usually made of erosion-resistant material such as concrete, of
a specific shape. Two common weir shapes are a 90° V-notch or a simple rectangular cutout. This
method for measuring discharge involves creating a dam just downstream of the weir. This dam
impounds in the weir, resulting in a more or less consistent stage height (e.g. a pool of more stagnant
water without complications determining height due to waves or ripples). Using the height of water in
the weir, one can determine discharge using one of the following empirically-derived equations :
For Rectangular weir,
𝑄 = 3.33(𝐿 − 0.2𝐻)𝐻3/2
The above formula is used for measurements in feet.
𝑄 = 1.84(𝐿 − 0.2𝐻)𝐻2/3
The above formula is used for measurements in meter.
For 90° V-notch weir,
𝑄 = 2.5𝐻5/2
For measurements in feet.
𝑄 = 1.379𝐻5/2
For measurements in meter.
Rectangular Weir and V Notch weirs for measuring flow

6. 6. BUCKETMETHOD
The Bucket method is a simple way to measure the flow rate using household items. It requires a
stopwatch, a large bucket, and preferably two to three people. To measure the flow rate using the
bucket method:
 Measure the volume of the bucket or container. Keep in mind that a typical 5 gallon bucket is
often actually less than 5 gallons.
 Find a location along the stream that has a
waterfall. If none can be found, a waterfall can
be constructed using a weir (see Figure Four).
 With a stopwatch, time how long it takes the
waterfall to fill the bucket with water. Start the
stopwatch simultaneously with the start of the
bucket being filled and stop the stopwatch when
the bucket fills. The bucket should not be filled
by holding it below the surface of the stream
because it is not the true flow rate.
 Record the time it takes to fill the bucket.
 Repeat steps two and three about six or seven
times and take the average. It is a good idea to
do a few trial runs before recording any data so that one can get a feel for the timing and
measurements required.
 Only eliminate data if major problems arise such as debris from the stream interfering with the
flow.
 The flow rate is the volume of the bucket divided by the average time it took to fill the bucket.
In thismethodthe Steamflowrate isdeterminedbyusingthe formula:
𝑄 =
𝑉
𝑇
Where,
Q= Streamflow in cubic unitsper second
V= Volumefilled in the bucketduring the time
T= Time estimated for thebucketfilling up to a certain level

7. 7. METERS
Metersare devicesthatmeasure the streamflow bydirectlymeasuringthe current.There are manydifferent
typesof metersbythe most commonisthe Pygmymeter,the vortex meter,the flowprobe,andthe current
meter:Theyare brieflydescribedbelow.
7.1 PYGMY METER
a wheel isrotatedbywaterflowandthe rate of the
rotationsignifiesthe watervelocity.Itisprimarilyusedin
measuringdischarge.
PYGMY METER
7.2 Vortex meter
Velocityisproportional tothe downstreamfrequencyof
the vortex flowandisread ona digital readout.Itis used
for measuringflowinpipes.
VORTEX METER
7.3 Current meter
Electronicpulsesdetermine watervelocity.Canbe usedin
large bodiesof waterlike oceanstomeasure the current.
CURRENT METER