This document discusses methods for measuring stream flow. It describes what a stream and drainage basin are and defines stream flow as surface runoff. Direct stream flow measurement methods include area-velocity, dilution technique, and current meter methods. Indirect methods use hydraulic structures like weirs and the slope-area method. Current meters are commonly used to measure velocity and must be calibrated. The area-velocity method divides the cross section into segments and multiplies width, depth, and velocity to calculate discharge. Dilution techniques use tracers added to the stream. A stage-discharge relationship can also be developed using indirect stage measurement methods.

1. Hydrology
CEN 363
Credit : 3.00
Md. Mehedi Hassan Masum
Lecturer
Department of Civil Engineering
Port City International University
Stream Flow

2. Introduction of stream flow
•Stream - flow channel into which surface runoff from a
specified basin drains
• A river drains the water collected from a specific area, which is called its ‘catchment
area’.
• An area drained by a river and its tributaries is called a drainage basin.
• The boundary line separating one drainage basin from the other is known as the
watershed.
• The catchments of large rivers are called river basins while those of small rivulets and
rills are often referred to as watersheds.
•Stream flow – runoff
• Measurement - fairly accurate
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3. Stream flow measurement
•Direct determination (time consuming and costly)
• Area velocity
• Dilution technique
• Electromagnetic method
• Ultrasonic method
•Indirect determination
• Hydraulic structures
• Slope-area method
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4. Velocity measurement
•Commonly used device is current meter
•Float can also be used for approximate measurement
•Current meter consists of a rotating element
• Vertical-axis
• Horizontal-axis
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5. • Calibration
• Relation between stream velocity and revolutions per sec
• Field use
• Shallow stream (depth up to 3 m)
• Moderately deep – two point measurement at 0.2 and 0.8 times of depth. Avg
velocity
• Rivers having flood flow, only surface velocity is measured within a depth of
0.5m below the surface. Avg velocity is K times vs.
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Velocity measurement

6. Discharge measurement
• Area – velocity method
• Measurement of area of X-sec
• Measurement of velocity
• Method is suitable, when
• Stream have a well-defined cross section and does not change in various season
• Easily accessible throughout the year
• -- Straight and stable reach
• -- Gauging site should be free from back water effect
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7. •Cross section is divided into a number of sub
sections by verticals
•Avg velocity of these sub-sections are measured
by current meter
• Segment width should not be greater than 1/15 to 1/20 of river width
• Q segment should be less than 10% of total Q
• Difference in velocity in adjacent segment should not be more than 20%
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Discharge measurement

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Department of CEN, PCIU
Discharge measurement

9. Department of CEN, PCIU
Discharge measurement

10. •Moving-boat method for velocity measurement in area-
velocity method
• A special current meter of the propeller type in which the velocity and inclination of
the meter to the boat direction θ in the horizontal plane can be measured, is selected.
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Discharge measurement

11. •Dilution technique of stream flow measurement
•Tracer should be
• Not absorbed
• Non toxic
• Capable of being detected in small concentration
• Not expensive
• Types of tracer
• Chemical (salt)
• Fluorescent dye
• Radioactive material
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Discharge measurement

12. Indirect methods
• Flow measuring structure
• Notch, weir, flume, sluice gate etc.
• Slope area method-
Frictional loss, hf and length of the reach, L
n = Manning’s roughness coefficient
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13. Stage-discharge
•First a stage-discharge relationship (rating -
curve) is developed
•Then only stage is measured, which is easy,
inexpensive and continuous reading can be taken
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14. Stage measurement
• Elevation measurement from a fixed graduated staff
• Normally the staff is fixed to a rigid structure like abutment, pier wall
• If one staff is not sufficient
use of sectional staff
• Wire gauge
• From a bridge, a weight is lowered
by a reel to touch the water surface
• Automatic stage recorder
• Float-gauge recorder
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15. Stage discharge relationship
•Plot stage versus discharge
• Gives a relationship representing integrated effect of a wide
range of channel and flow parameter
• Combined effect of these parameters are known as control
• If control does not change with time  permanent control
• Otherwise shifting control
•Easy to measure discharge
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