Port Surveying
Hydrographic and land surveying for port projects. El-Eman Office provides coastal and marine surveying.
Planning a Hydrographic Survey in a Port
Before the survey boat goes into the water, the purpose of the survey must be clear: tracking dredging, checking the depth alongside quays, or producing a navigation chart. The purpose sets the line spacing, the type of instrument and the accuracy required. Survey lines are normally run perpendicular to the quay or the navigation channel, with cross-check lines that reveal any systematic measurement error.
- Define the survey limits and the nearest approved ground control points.
- Choose the coordinate system and the vertical reference to which depths will be tied.
- Assess sea state, wind and currents that could affect measurement quality.
- Obtain access permits and coordinate ship movements with the port authority.
Calibrating Instruments and Correcting Measurements
An echo sounder measures depth using the speed of sound in water, and that speed changes with temperature, salinity and depth. Surveyors therefore calibrate the instrument daily, using a sound velocity probe or a bar check, and apply the correction to the data. Vessel motion (heave, pitch and roll) is also recorded and the measurements are corrected accordingly.
Tidal correction is one of the most important adjustments. Recorded depths depend on the water level at the moment of measurement, so they must be reduced to a fixed reference level before two surveys taken at different times can be compared. A tide gauge close to the work area or a correction based on GNSS measurements is used for this.
Linking Marine and Land Surveys
A project loses its value if the depth chart is in one coordinate system and the quay levels are in another. The two sides must be tied to shared control points so that the shoreline, the quay edge and the basin floor appear on one consistent map. At the quay edge, the echo-sounder depth is checked against a direct tape or hanging-level measurement.
Common mistakes in this type of project include:
- Ignoring tidal correction, which creates false differences between two surveys.
- Not calibrating the sound velocity on the day of the survey.
- Leaving gaps between survey lines near quay edges that are hard for the boat to reach.
- Mixing marine datum levels with land levels without stating which is which.
Documenting Results and Handing Over Data
A survey is not finished with a single drawing. Deliverables usually include depth contour charts, digital terrain models of the seabed and a technical report describing the instruments, calibration, the vertical reference and possible sources of error. Comparing two consecutive surveys helps calculate siltation or dredged volumes, provided both use the same reference and accuracy. Raw data should be kept so it can be reprocessed if needed. Older quays also need an underwater inspection for scour or voids at their base, which a land survey cannot show.
Frequently asked questions
What is the difference between single-beam and multibeam surveying?
A single-beam sounder measures depth directly beneath the boat along one line, so closely spaced lines are needed to cover an area. A multibeam system covers a wide swath of the seabed in one pass, gives a fuller picture and detects small obstructions, but it costs more and produces much more data to process.
How often should a port be re-surveyed?
There is no fixed interval. It depends on how fast sediment accumulates, on dredging activity and on traffic. Areas that silt up quickly are surveyed more regularly, and a survey is also sensible after a severe storm or before receiving deep-draught vessels.
Is a hydrographic survey enough to design a new quay?
No. It only defines the shape of the seabed. Design also needs investigation of the soil beneath the seabed, a study of waves and currents, and a land survey of the back area. The hydrographic survey is one input in a wider data package.
