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IRD
Institute of Research for Development
NEW TECHNOLOGIES IN SURFACE HYDROLOGY
Data Acquisition and Data Processing
Abstract of the training course
1 - HYDRO- METEOROLOGICAL DATA ACQUISITION - TELEMETRY
The use of software is standard in modern hydrological services all over the world. It is obvious that such software are not fully utilised if preceding inputs are manually tabulated. It is more profitable to be able to input data directly into the computer system in the original field acquisition and storage format, without human interference. This system saves a lot of time and results in faultless data transfer.
Having briefly treated conventional field equipment the different types of new generation equipment (data loggers) are considered :
- encoder for water level recorder by float
- pressure sensors
- bubble system water level recorder, etc.
The main parts of the data loggers are studied:
- the interface
- the clock
- the control circuit
- the memory
- the power supply
- the sensor.
The introduction of telemetry completes the efficiency of the data loggers. The main telemetry systems such as phone, radio and satellite are presented. A particular detailed study of telemetry by satellites using the two main systems : ARGOS and METEOSAT is carried out.
2 - DISCHARGE MEASUREMENT
River discharge, which is expressed as a volume per time unit, is the rate at which water flows through a cross section. Discharge at a given time can be measured by several different methods, and the choice of methods depends on the conditions encountered at a particular site.
This course proposed a detailed study of the different methods, both conventional as well as more recent methods using new technologies equipment, and the limits of each method in their field of application.
Discharge measurement using a current meter
One point method ; multiple point method ; integration method; *Independent Vertical Rating method.
Independent Vertical Rating method is particularly convenient for discharge measurement at the outlet of small catchments or in case of flash floods in larger catchments. It allows the calibration of rating curves in good conditions, with a higher precision in the upper part of the curve, and an interesting knowledge of the vertical distribution velocities through the cross section, very important for improving float measurement results.
Discharge measurement using floats
Discharge measurement using new technologies equipment
Ultrasonic method ; intelligent sounding weight ; Acoustic Doppler Current Profiler.
Hydraulic formula
3 - RATING CURVE CALIBRATION
The rating curve calibration is the last step in the primary data field collection and process. The accuracy of the rating curve calibration is very important as all the further calculations, mathematical modelling, etc. are based on this calibration.
A detailed analysis of the hydrometric station file, of the river bed geometry, of the hydraulic conditions must be done before drawing the rating curve. Different methods have to be used for the extension in the upper part and the lower part of the rating curve.
During this course a full study of rating curve calibration will be carried out step by step from the hydrometric station file examination, the discharge measurement check, the hydraulic flow conditions to the final extension of the rating curve. Different methods such as logarithmic method, Slope-area, Conveyance, Stevens, approximation of Cease To Flow, etc. will be applied.
The limits of each method in their range of application will be defined during the hands-on exercises.
4 - LEVELLING SURVEY
The experience in the field data collection shows that the field teams must be equipped with survey levels and staves. Without survey input only 50% of the information available at the hydrometric station site is collected, thereby generating problems with rating curve identification and data processing.
Theoretical courses are proposed on the interest, the use (hydraulic formula, etc.) and the methodology of levelling survey, but also a large part of hands-on exercises in the field and calculations.
A specific item on GPS use will be included in this program.
5 - BATHYMETRY
The proposed methodology is applicable for discharge measurements in wide rivers (it was used for example on the Amazon river and on the Congo river), but also for bathymetry works on lakes and dams for silting evaluation studies.
The technique consists of successive crossings, the depth graph being continuously recorded by an ultrasonic transducer device, the boat positions on the cross-section being plotted from time to time by theodolite readings from the bank.
Having mastered the theory of the method, an exercise in the field will be carried out in order to use the different equipment to record data. Calculation will be carried out using the field data collected.
6 - RAINFALL-RUNOFF RELATIONSHIP ON SMALL CATCHMENT
Use of the method of the mini-rainfall-simulator
This method is used by the IRD hydrologists since many years for rainfall-runoff relationship studies on small catchments, but it's also a didactic experiment for the understanding of the infiltration and runoff phenomena.
The main aims of the rainfall simulation method are:
- an accurate analysis of the conditional factors of the infiltration and the runoff
- the study of the flood genesis
- a better use of the mathematical models that often require a calibration of observed values
- the study of the effect of the different surface features, cultural practices, etc.
- the study of the soil erodibility.
The course is divided in three parts : the theory of the method and the applications, a field experiment, and calculations using the field data collected.