The shortest definition for hydrographic survey is surveying water bodies. It deals with the measurement of physical characteristics of surface and subsurface water bodies, i.e. boundaries (X, Y coordinates) depth (Z coordinate), surface level (Z coordinate) as well as other measurements like flow velocity, sampling of river bed and suspended sediment materials. As it is important to be aware of the fact that, the quality of any study is only as good as the quality of the information gained through the data collected, and the influence of any error incurred during the measurements leads to limiting the accuracy of the study, a highly trained researchers and technicians equipped by up to date surveying equipments are responsible for the data collection. HRI developed surveying system that proofed high quality performance. The following is a summarize of this system.
MAJOR ELEMENTS OF HYDROGRAPHIC SURVEY
Field measurement campaign, hydrographic survey consists of three phases:- Design
- Field work
- positioning of surface objects (edge of water, pillars of bridges etc.; X, Y and Z coordinates)
- positioning of subsurface (under-water) objects (X,Y and Z coordinates) – water depth measurements
- recording flow velocities.
- Data Analysis, Processing and Quality Checks
- A reference point data which is the raw data of the GPS units that fixed on the reference Bench Mark point.
- A Bench marks data which is the raw data of the Fixed GPS units that identifying the position of these Bench Marks
- Topographic data which is the raw data of the Rover GPS units that leveling the banks, the islands and the water-line.
- Bathymetric data which is the raw data of the Rover GPS unit that equipped on the boat to identify the coordinates of bathymetric pass and the water depths data that collected from the echo-sounder during this pass.
- Data quality checks and compilation
- Checking the closure error of leveling the constructed benchmark. The maximum acceptable error not exceeds 3mm.
- Filtering the errors of the bathymetric survey depths, simply by mentoring it even on computer screen or in hard print-out.
- Filtering the errors of the measuring points coordinates which is with ambiguity status no.
- Checking that the results of the re-surveyed area (overlap area between two days of measurements) is acceptable.
In the design phase, maps, aerial photographs and other pieces of information (e.g. results of previous campaigns) are used to define where and how the measurements will take place. It is always useful to have an inspection of the area to have the most up-to-date insight into the circumstances, to minimise the unforeseeable difficulties. The output of this phase is a measurement plan in forms of charts, time planning, personnel and budget estimates.
During the field work, the following measurements are taken and documented:
After the data has been collected from the site the data processing stage then started to produce a day by day dataset in the form of:
The GPS software allows processing GPS observations that have been recorded in the field to achieve their coordinates and their relative accuracy. The data to be processed may be selected graphically. All selected data is processed automatically in a batch process without the need for any user interaction.
All rover points are listed together with its coordinates, quality and the ambiguity status. The Ambiguity Status is an essential indicator for the accuracy of measuring point. It indicates that the determination of the integer number of cycles between the satellites and the GPS receiver was successful.
After the data processing is completed the results can be viewed and stored for further use in the results-view in the form of a file contains X-Y-Z for the topographic data where Z is the point level and X-Y-T for the bathymetric data where T is the measuring time.
The water depth results can be collected from the data logger of the echo-sounder in the form a file contains D-T where D, is the water depth and T, is the measuring time. By matching the two files of the bathymetric data and the echo-sounder data with respect to the time of measurement T, a new file contains X-Y-D can be produces
Quality checks for the measured data are carried out at the end of each survey day to meet the accuracy requirements. It is important to be aware of the fact that the quality of the total study is only as good as the quality of the information gained through the collected data. Thus, the influence of any error incurred during the measurements leads to limiting the accuracy of the study. Therefore the following checks are daily conducted:
After the daily data set is analyzed, processed and checked for any errors the whole data for the over all period of data collection is compiled. One input file is prepared per each data type, bathymetric data, topographic data (left and right banks of the river reach), benchmarks and hydraulics structures data.
EQUIPMENTS:
The department has up to date surveying equipments as follow:DIFFERENTIAL GEOGRAPHICAL POSITIONING SYSTEM (DGPS)
| Model: | LEIKA GPS 300&500 |
| Description: | For measuring the global coordinates. It is also used for monitoring and recording the boat position as well as the bed level (output of the echo sounder). The data acquisition is done by the computer. |
| Range: | 0-100 km |
| Accuracy: | ± 0.10 m |
| Model: | LEIKA, TS 1700, SWISS |
| Description: | It is used for measuring the horizontal distances, horizontal, vertical angles and target coordinates. The data is recorded on a special tab using a built-in recording system. The data is easily transferred to the computer. The system is operated by a rechargeable battery. The battery life is 8 hours. |
| Range: | 0-5 km |
| Accuracy: | ±0.002 m and 1.5 degree |
| Manufacturer: | METOROLLA, USA |
| Model | Falcon IV |
| Description: | It is used for measuring the horizontal distances and horizontal angle with north direction. The data is recorded on a special tab using a built-in recording system. The data is easily transferred to the computer. |
| Range: | 75 km |
| Accuracy: | ± 2 m |
| Manufacturer: | TAMAYA TECHNICS INC., JAPAN. |
| Model | TDM-9000 |
| Description: | It is a compact and advanced precision echo-sounder. It is used for measuring the bottom profile. The instrument is connected to a pen recorder for plotting the sea bed configurations. |
| Range: | 0.70-100 m |
| Accuracy: | ± 0.03 m |
| Manufacturer: | SonTek and Argonaut, USA |
| Model | The Argonaut-XR |
| Description: | For current and wave measurements and current profiling |
| Range: |
Accuracy: (0.016 ft/s) ±1% of measured velocity, ±0.5 cm/s Accuracy = 0.1% Reflected echo intensity output Compass/two-axis tilt sensor Temperature sensor on exposed titanium pin for fast response Son Wave real-time non-directional wave spectra package |
| Manufacturer: | DH,(Netherlands)-HRI, (Egypt) |
| Model | Sampler |
| Description: | For Sediment Transport measurements |
- Fiber Rubber boats
- Power boats
Different boats were used in the bathymetric survey with capacity up to 7 persons, and 55 HP outboard motors.
The dimensions of the boats are:Item |
Dimensions |
|
Big Boats |
Small Boats |
|
Length |
4.7 m |
3.96 m |
Width |
1.90 m |
1.68 m |
Draft |
0.25 m |
0.20 m |
Capacity |
0.70 ton |
0.50 ton |
Motor |
55HP |
40HP |
To have suitable space for personnel, work area and instruments, as well as sufficient generating capacity to operate the equipment on board for calibration, checking and data retrieval. The boats have sufficient fuel capacity to allow for a full day's activities with minimum refueling time.
SEDIMENT LABORATORY
A sediment laboratory is available for analysis of bed and suspe nded sediment samples. Sieve analysis and pipette tube are used for determining grain size distribution for sediments. Also the laboratory is provided with other instruments such as Owens, scale, ....etc.
Key Person:
Dr. Ahmed Mostafa Amin Email : a.amin@hri-egypt.org