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Specifications   Hydrology Project   Surface Water
 
Specifications for Surface Water Equipment
 
Measuring water level

Water level (or stage) is the elevation of water surface above an established datum. Records of water level are used with a stage-discharge relationship to compute the river flow (or discharge).

Staff gauge - The simplest measurement uses manually-read level gauges, the most common of which is the vertical staff gauge which is simple, robust and easily understood. Other types include inclined/ramp staff gauges, crest staff gauges for maximum water level, and electric tape gauges. An observer reads the gauge at the same time(s) each day, and reports the quantity as a water level.
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Float in a stilling well - measures water level by the movement of a float in a stilling well connected to the river such that the water levels in the river and the stilling well are the same. The float is usually connected to a chart recorder (from which an observer manually extracts water levels at the required time interval) or a shaft encoder (which provides a digital recording of float movements).
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Gas bubbler system - measures water level by the pressure of gas needed to release bubbles at the tip of a pipe in the centre of the river. The bubbler is usually connected to a chart recorder (from which an observer manually extracts water levels at the required time interval) or a shaft encoder (which provides a digital recording of float movements).
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Pressure transducer - a pressure sensor located on the bed of the river which measures water level by the pressure of water above. The logger can be set to record data at the required time interval.
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Radar - a radar instrument mounted vertically above the water surface which measures distance to the water surface by analysis of a reflected signal). The logger can be set to record data at the required time interval.
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Comparison table for different types of water level sensor at end

Measuring flow

Spot measurements of water level and river flow are used to develop a stage-discharge relationship which can be used to convert water level data into river flow.

Current metering - the rotating element (impeller or cup-type) meter is the most commonly used method of velocity measurement in India. Flow is derived from the mean velocity and cross-sectional area. Electromagnetic current meters also exist.
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Float methods - the simplest, cheapest and earliest form of flow measurement, though less accurate than other methods. The technique involves the timing of floats over a measured length of uniform river reach. Flow is derived from the mean surface water velocity and cross-sectional area. Floats are not as accurate (+/-20%) as current meters and ADCPs.

Acoustic Doppler Current Profiler (ADCP) - a rapid, accurate (+/-10%) and increasingly used method of direct flow measurement. The velocity throughout the water column is measured by a method based on the Doppler effect of sound waves scattered on particles suspended in the water, and combined with measurements of depth and ADCP movement. The recommended ADCPs are manufactured by Sontek and Teledyne RDI.
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Slope-area methods - a method based on open channel formulae for estimating velocity using surface water slope and channel geometry (e.g. Manning's formula), traditionally used to estimate peak discharges when it is not possible to make flow measurements by the other means listed above. Flow is derived from the mean velocity and cross-sectional area. Slope-area methods are not as accurate (+/-25%) as current meters and ADCPs.

Artificial control - different flow measuring structures include thin plate weirs, broad-crested weirs, triangular profile weirs, compound weirs, flumes, and reservoir spillways, sluice gates and other control structures. Structures have a high capital cost, but are highly accurate (+/-5%) providing the flow is within the modular range of the structure.

Specifications for other surface water equipment and instruments can be downloaded from the links below

Item ID
Approval Date
ACOUSTIC DOPPLER CURRENT PROFILER
10.021 July 2009
ADCP PROCUREMENT NOTE
10.021A Pending
ALUMINIUM BOAT (6M)
10.035 May 1998
AUTO LEVEL 10.028 October 1999
AWLR, FLOAT TYPE WITH CHART (SW)
10.004 July 2009
BATHYMETRY SOFTWARE
10.018 May 1998
BATHYMETRY SYSTEM 10.013 May 1998
BOAT OUTFIT 10.032 April 1999
BOAT TRAILER
10.037 May 1998
BRIDGE OUTFIT 10.031 April 1999
CABLEWAY GUIDANCE NOTE 1 - DESIGN   N/A

CABLEWAY GUIDANCE NOTE 2 - DRAFT SPECIFICATION

10.030 N/A
COMPASS
10.023 May 1998
CURRENT METER, CUP TYPE 10.007 October 2007
CURRENT METER, ELECTROMAGNETIC 10.022 May 1998
CURRENT METER, ELECTROMAGNETIC (WADING USE) 10.050 October 1999
CURRENT METER, PROPELLER TYPE 10.009 October 2007
CURRENT METER, PYGMY TYPE 10.008 May 1998
DATA RETRIEVAL SYSTEM 10.044 July 2009
DIFFERENTIAL GPS September 2010
DIGITAL CAMERA Pending
DWLR, BUBBLER TYPE (SW) 10.045 July 2099
DWLR, FLOAT TYPE WITH SHAFT ENCODER (SW) 10.045 July 2009
DWLR, PRESSURE TYPE (SW) 10.005 July 2009
ELECTRICAL LEVEL INDICATOR TAPE 10.003 October 2007
ELECTRONIC STOPWATCH 10.011 October 2007
FRP BOAT (5.5M) 10.047 August 1999
FRP BOAT (7M) 10.033 May 1998
FRP CATAMARAN (8M) 10.034 May 1998
GPS, HANDHELD July 2009
HYDROGRAPHIC ECHO-SOUNDER 10.014 May 1998
LASER DISTANCE METER 10.029 May 1998
LEVEL INDICATOR TAPE 10.002 October 2007
LEVELLING STAFF 10.027 May 1998
MOTOR LAUNCH 10.051 October 1999
OUTBOARD ENGINE 10.036 May 1998
PORTABLE ECHO-SOUNDER 10.012 August 1999
PORTABLE GENERATOR 10.019 May 1998
PULSE COUNTER 10.010 November 2000
SOUND VELOCITY CALIBRATOR 10.015 May 1998
STAFF GAUGE 10.001 May 1998
STEEL BOAT (5.5M) 10.048 August 1999
STEEL BOAT (8M) 10.049 August 1999
SURVEY EQUIPMENT 10.025 May 1998
TENT 10.038 May 1998
THEODOLITE 10.026 October 1999
TOTAL STATION 10.041 May 2010