Water Measurement Techniques

HELLO

South Africa

Drainage Regions

Solution…

• Ancient Farmer’s Method• Today’s DWA Method

Techniquesand

Instrumentationused for

Flow Measurement

By: Mzukhona Hlazo

Hydrometry Services

• Design & Construct structures• Install instrumentation• Provide the data

Outline

• Acoustic Doppler Profiler• Gauging structures• Measuring instruments• Site Visit

Acoustic Doppler Profiler

• Used to:• Measure Velocity, depth & calculate flow (Q)• During floods when gauging weirs fail• To verify a gauging structure’s measurements

History

• Manual way (paper, measuring tape, stopwatch): Velocity= • Then: Flow (Q)= Area x Velocity• Mechanical propeller

Acoustic Doppler Profiler

• Uses wave technology (ultrasonic sound)• Doppler effect:

•f= x fo

Acoustic Doppler Profiler

Velocity of

source

Emitted wave Velocity

of receiver

Observed wave

Left Bank Right BankDirection of movement

Components• Boat• Transducer (SonTek M9)

• PCM (Base station for power)• GPS System• Laptop• Computer programme (River Survey)• Communication

• Direct connection (cable)• Bluetooth (200m)• Spread spectrum (2km)

Measuring Procedure• Set the programme• Calibrate compass• Minimum of 3 people

• 2 in river• 1 on laptop

• Remember: 1 accurate reading = 4 Transects• NB: Velocity of the boat < velocity of water

Challenges

• Negative results• Because of moving bed sediment

• Solved by using a GPS (RTC station)

Site selection

• There should be no:• Bends• Rocks• Vegetation on river bed• Clear water• Uniform flow

Gauging Weirs

• Used to get the stage:• Stage is height of water above low notch (crest)• Stage is then used in Discharge Table to get the Flow (Q)

ComponentsUpstream gauge plate

Downstream gauge plate

Hydraulic jumpand

Super critical flow

Clear pool lengthAnd

Sub-critical flow

Gauging structures

• Sharp Crested• Broad Crested• Crump & V-Crump• Hydro Flume• O-Gee Crested

Formulas for Design (Crump Weir)

• Froude number: Fr=• Energy Head: H= h + (Bernoulli's formula)• Gauge plate position: 2 x Hd (upstream) & 10 x (Hd + Z)

(downstream)• Flow: Q = 1.981 x b x H1,5

• Pool characteristics:• Minimum Length: 5 x length of structure• Minimum Depth:

Site selection• Longitudinal Section• Easy Access• Straight• Froude number (subcritical flow)• Pool length• Width of river• Vegetation in water• Obstructions (Down stream)

• No swamps or wetlands• No dumping sites nearby

Maintenance• Remove debris & island (upstream and downstream)• Remove vegetation growth• Clean Gauge plate

Gauge Plate (Parent)• Metal plate (1m long & 300mm wide)• Used to measure the stage• Invert level = crest of structure (low-notch)• Placed against a structure or as a stand alone• Must be cleaned or replaced when dirty• Used to calibrate instruments and double check their

readings• Position: use formula depending on structure (e.g. 2 x Hd for

upstream)

Type X

• Float and counter-weight method• Records on a chat (graph)• Heavy maintenance

• Changing of chats (every two weeks)• Tracing data into computer

• Not effecting in high siltation sites

Thalimedes

• Manufactured by OTT• Replacement of the TypeX• Float and counter-weight• Uses a shaft encoder• Stores electronically

• Stores for 8 months (then starts to over write)

Stilling Well• For Float and Counter-weight systems

Position of Inlet pipe• Must be inline with gauge plate, centre of the pipe crown must be at invert of plate.

STS pressure transducer• Works on the pressure principle• Has two parts:

• A sensor part (with diaphragm)• Has ranges from 0-4m up to 0-100m

• Logger part• Uses a signal of 4 – 20mA (so is be supplied by Alkaline batteries)• Needs a laptop/PDA to retrieve data

Pressure principle

Atmospheric pressure

Water pressure

Pressure principle

Loggers

• Data Collection Platform (looks like an electric circuit)• Power supply

• Battery (12v)• Solar panel

• Kept clean• Protect from vandalism

• Power regulator• Surge protection• GSM/GPRS communication• Logger (Logo Sens/Dou Sens)

Loggers cont.

• Fault finding• Use multi meter• Follow current and voltage

Cello

• Good in signal strength• Can act as a multi logger

Weather station

• Help estimate water inflow (precipitation)• Rain gauge (Tipping Bucket)• Anemometer (Wind speed & direction)• Barometer ( Atmospheric pressure)• Viewing screen

Basic tools to take along

• Keys for the recorder hut• Inspection form• Camera (to take pictures of damages)• Laptop/PDA & DouLink cable• Multi meter (to check power for DCP)

• For STS pressure transducers laptop will show the remaining power

Site Visits• Goosen Bay Canyon on the Vaal River

Conclusion

What WhyWhere Ho

w

Who When

?

The End!!!

• Remember: if you can’t measure, you cant control…

Questions?