The project involves comprehensive works to provide a supply of seawater for industrial purposes in the Special Economic Zone at Duqm, Sultanate of Oman. The aim of the Marine Survey is to characterize the shore approach, bathymetric conditions, water quality, geophysical aspects, and met-ocean conditions of the site necessary for the design of seawater intake and outfall structures north of Duqm Port.

Scope of Work

• Bathymetric survey using single beam echo-sounder, or other approved equipment, for depths below 5 m with an accuracy of ±0.1m and a positional accuracy of ±0.5m. Survey area covered at a grid spacing of 15m x 15m. Three (3) locations, each 160 m wide, were surveyed in higher resolution.
• Tide recordings taken at frequent intervals for accurate soundings.
• Horizontal positioning controlled by Differential Global Positioning System (DGPS).
• Survey to be reported at a scale of 1:2500, tied into the national grid system and national vertical control datum, as well as Admiralty Chart Datum.
• Survey of existing shoreline topography including the inter-tidal zone to correlate with the bathymetric survey.
• All data subject to quality control according to IHO S-44 standard, order 1a.
• Deployment of 4 ADCPs for a full lunar cycle at a depth of -12m CD, and 2 Wave and Current meter buoys for one month at a depth of -20cm CD.
• Collection of water and sediment samples from 50 locations, with sampling conducted in both summer and winter seasons.
• Geophysical survey including seismic and side scan surveys.
• Collection of 20 water samples for analyzing suspended sediment concentration.
• Measurement of water quality parameters such as salinity, pH, dissolved oxygen, and turbidity at 15 locations.

Equipment List

• Teledyne Odom’s Echotrac MKIII (Survey Depth Collection Sonar)
• Valeport Tide Gauge
• RDI Teledyne ADCP Current Meter
• GeoPulse GeoAcoustics Pinger
• Van Veen Grab (Sediment Sampler)
• Niskin Water Sampler
• Midas CTD+ (Conductivity, Temperature, and Depth Data)
• VideoRay Pro III XE GTO ROV System
• Oceantools VO-5 Video Overlay
• 14" Composite Video Monitor
• Pioneer DVD Recorder

Data Collection Systems

• Sokkia RTK GPS Receiver - BASE (Survey Navigation Positioning and Benchmark Positioning)
• Sokkia RTK GPS Receiver - Rover (Survey Navigation Positioning and Benchmark Positioning)
• ADL Vantage Pro - Pacific Crest (Wireless Digital Data Link)
• Hemisphere DGPS (Survey Navigation Positioning)

Survey Methodology

Water and Sediment Sampling

The Van Veen grab is a lightweight sampler designed to collect large samples from soft bottoms. Its long lever arms and sharp cutting edges enable it to cut deeply into softer bottoms. The grab is manufactured in two sizes from stainless steel with weighted jaws and chain suspension to ensure vertical descent and minimize disturbance.

Samples were collected at surface, mid-depth, and bottom using a Niskin water sampler. The Niskin sampler uses rubber tubes to seal and can be used singly or in series, or mounted in a rack (rosette).

Bathymetry

A pre-survey investigation ensured a safe working area and met the client’s survey objectives within pre-defined areas. A Valeport Tide Gauge was installed for tide correction. An Odom Echotrack MK III Dual Frequency Echo Sounder was utilized with 210 kHz and 33 kHz digital output logged by the navigation computer. CTDS dips and bar checks were conducted daily. The Hemisphere Sokkia RTK system was used with HydroPro software for converting antenna positions into local UTM projection coordinates.

Current and Wave Measurement

Current speed and direction were measured using an RDI-Teledyne ADCP current meter over a 30-day period, with data recorded at 10-minute intervals. Wave and current meter buoys were deployed for one month to measure wave and current conditions.

Geophysical Survey

Side Scan Sonar was tested and deployed according to the manufacturer’s instructions. The towfish was towed behind the survey vessel, with the cable length adjusted for water depth. RTK GPS was used to record exact coordinates, and data were continuously recorded using CODA survey software in .SGY format, converted to .COD format for processing.

Sediment Sampling

Sediment samples were collected using the Van Veen grab sampler. Samples were taken from various depths and analyzed for nutrients, heavy metals, and hydrocarbons.

Results

The bathymetric data were collected and processed using the HydroPro software. The project successfully characterized the shore approach, bathymetric conditions, water quality, and geophysical aspects of the site. The seabed features and conditions have been well documented and analyzed to support the design of seawater intake and outfall structures.