Streamflow gauges.pptx for lab course, civil engineering
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- 2. INTRODUCTION TO STREAMFLOW GAUGES • DEFINITION: The measurement of discharge and stage (depth) in a stream is referred to as stream flow gauging. • The instruments and some structures used for the measurements of flow or discharge are termed as stream flow gauges. 2
- 3. TYPES OF STREAMFLOW GAUGES • There are four main types of stream flow gauges which are further subdivided. 1. Non recording gauges or manual gauges. 2. Recording gauges or automatic gauges. 3. Wiers, Notches. 4. Flumes. 3
- 4. 4 NON RECORDING GAUGES Non recording gauges are of two types. 1. Staff gauges. 2. Wire weight gauge. Staff gauge is further divided as 1. Immersed staff gauge. 2. Short sections staff gauge. 3. Inclined staff gauge.
- 5. 5 NON RECORDING GAUGES(cont…) • IMMERSED STAFF GAUGE: A staff gauge is set so that a portion is immersed in water in all the times. The gauge may consists of a vertical scale attached to bridge pier, pilling or other structure that extends into a low water channel of the stream.
- 6. 6 NON RECORDING GAUGES(cont…) Immersed staff gauge staff gauge
- 7. 7 NON RECORDING GAUGES(cont…) • SHORT SECTION STAFF GAUGE: – If no suitable structure exists in a location accessible at all depths, a section staff gauge may be used. – Short sections of staff are mounted on available structures or on specially constructed supports. in such a way that one section is always accessible.
- 8. 8 NON RECORDING GAUGES(cont…) SHORT SECTION STAFF GAUGE
- 9. 9 NON RECORDING GAUGES(cont…) INCLINED STAFF GAUGE: • The inclined staff gauge is placed inclined along with the bank of the river and is consists of heavy timber.
- 10. 10 NON RECORDING GAUGES(cont…) • WIRE WEIGHT GAUGE: – In this type of gauge, a weight is lowered from a bridge or over head structure until it reaches the water surface. – By subtracting the line paid out from the elevation point of a fixed reference point on the structure, the water surface elevation can be determined.
- 11. 11 NON RECORDING GAUGES(cont…) weight weight moves up / down with water surface WIRE WEIGHT GAUGE
- 12. 12 RECORDING GAUGES • There are four types of recording gauges 1. Float gauge. 2. Bubble gauge recorder. 3. Crest water gauge recorder. 4. Current meters. 1. Price current meter. 2. Propeller current meter.
- 13. 13 RECORDING GAUGES(cont…) • FLOAT GAUGE: – This type of equipment is often located inside of a stilling well, and used to record the rise and fall of the water level. A float is attached to a pulley with tape, and the float is able to move with the watercourse level.
- 15. 15 RECORDING GAUGES(cont…) • Bubble Gauge Recorder: – The bubble-gauge recorder consists of an orifice attached to the stream bed through which gas is expelled and a measuring device , which measures the resistance to the release of the gas produced by the column of water above it. – A compressed gas normally nitrogen gas is used.
- 17. 17 RECORDING GAUGES(cont…) • CREST WATER GAUGE RECORDER: – During high floods staff gauges cannot measures the stage, they will be totally under water. For such conditions crest gauges provides information about the flood water level. – The gauge used by the USGS consists of a length of pipe containing a graduated stick and a small amount of granulated cork. – The cork floats as the water rises and some adheres to the stick at the highest level reached by the cork. – The stick is then removed and the reading is taken, then the cork is wiped of and the stick is replaced for the next time.
- 18. 18 RECORDING GAUGES(cont…) CREST WATER GAUGE RECORDER
- 19. 19 RECORDING GAUGES(cont…) • CURRENT METERS: – Current meters are the most commonly used instruments for measurements of flow velocities of stream water. – There are two types of current meters. 1. Price current meter 2. Propeller current meter
- 20. 20 RECORDING GAUGES(cont…) PRICE CURRENT METER: • It consists of 6 conical cups rotating about a vertical axis who has electric contacts, driven by the cups along with the recorder. • The circuit is closed through a battery and the wire of a supporting cable to cause a click for each revolution or each 5th revolution. • The clicks are recorded through headphones worn by the operator or some other electronic devices can be used.
- 21. 21 Rotating cups make clicking sound in headphones If current strong may need weight
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- 23. 23 RECORDING GAUGES(cont…) • PROPELLER CURRENT METER: • The contacting mechanism is similar to that of the price meter and similar suspension are made a;ong with some weight . • The difference is that it uses a propeller turning about a horizontal axis.
- 25. Current Meter 25
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- 28. 28 WEIRS • WEIRS: – These are the structures built into the stream that force the water to flow through an opening of a known size and shape. A weir includes all components of a stream gauging station as well as a notch control. – The notch can be V-Shaped or trapezoidal.
- 29. 29 WEIRS(CONT…)
- 30. 30 FLUMES • FLUMES: – Flumes are artificial open channels built to contain flow within a designed cross section and length. – There is no impoundment, but the height of water in the flume is measured with a stilling well. – Measurement of the height of water in the flume allows one to calculate discharge.
- 31. 31 FLUMES(cont…)