Application of ADCP to Ocean Current Measurement in Zanzibar Port

1. Where is Zanzibar Port

Zanzibar Port is located on the western coast of Unguja Island, part of the Zanzibar Archipelago in Tanzania. Thus, this is a very important strategic maritime gateway for the region.   Scale of the Port and Throughput It is an averagely-sized port, occupying a very important position in the economy of Zanzibar. It is a general cargo, container, and bulk commodity port. It handles quite a substantial amount of cargo every year, whose throughput is affected by factors such as the growth of local industries and international trade relations. For instance, it is a significant point of export for agricultural produce such as cloves, one of the major cash crops of Zanzibar, while vital items like machinery, building materials, and consumer goods are imported.

Shipping Routes and Services

International shipping routes serve the port, There are scheduled shipping services with ports in East Africa, the Middle East, and Europe. These services are provided by various shipping lines, facilitating the movement of goods both locally and globally. Some of the common shipping lines operating from here include MSC (Mediterranean Shipping Company) and CMA CGM. These lines offer different types of services, such as full-container load (FCL) and less-than-container load (LCL) services, to meet the diverse needs of shippers.

Port Management and Operation

The port in Zanzibar is managed by local port authorities. It ensures that there is smooth functioning of the port in terms of berthing, cargo handling, and security in the port area. It functions on a regular schedule with a specific number of working hours allocated for loading and unloading. This management also coordinates customs and other regulatory bodies to follow international trade regulations.

Port Facilities It contains modern berths that are able to handle ships of different sizes. It also contains a container terminal with the handling equipment that includes cranes and forklifts in loading and unloading containers with efficiency. Goods in transit can be stored using storage facilities, such as warehouses and open storage areas. Additionally, it would contain fueling stations to refuel ships, and minor repair facilities.

Waterways and Direct Navigation

The approach channels to the port are maintained for safe navigation. Depth of the channels is constantly checked, and dredging is done whenever necessary to accommodate vessels with draft up to a certain draft can enter the port. There are also navigational aids installed along the waterways such as buoys and lighthouses that help the ships while passing during day and night. The port has a direct entrance to the Indian Ocean, which links it directly with international shipping lanes.

2. Why measure the ocean currents in Zanzibar Port?

Navigation Safety

Ocean currents may immensely affect the movements of ships. In Zanzibar Port, precise knowledge of current patterns aids ships in routing their courses effectively. These strong currents might take a vessel off its intended course, particularly when the ship is in a place where berthing and unberthing are concerned. By monitoring the currents in the ocean, captains can adopt the necessary changes in speed and course for a safe and smooth docking of their ships. For example, with a strong incoming current, the ship has to approach the berth at a certain angle and speed to avoid hitting the pier.

Cargo Handling Efficiency

Currents can also disturb the stability of ships while cargo is being loaded and discharged. A current which is too strong will prevent a ship from holding an exact position next to loading gear, thereby slowing the pace of the operations of cargo handling. The efficiency of a port would increase since by understanding in advance the state of currents, the port operator is able to plan cargo handling during those times when currents are relatively stable.

Protection of the Marine Ecosystem

The understanding of the currents also forms a foundation for protection of the marine ecosystem both inside and around the port. The nature of the current causes spreading of pollutants, movements of marine organisms, and the distribution of nutrients.

Currents can be measured by environmentalists to predict the ways in which pollutants from the port, like oil spills or chemical waste, will spread through the water. This information gives a way through which strategies might be developed minimizing the impact of this on marine life. With this knowledge in mind, regarding the current-should a given pollutant take hold, help can be assessed regarding the spots that are mostly affected, a more specific method of response shall be created thereby.

Modern and Efficient

Acoustic Doppler Current Profiler(ADCP) Among the many methods of measurement, the ADCP is relatively newer and easier to use in measuring ocean currents. ADCPs are capable of measuring current speed and direction at very high resolutions in real time-a very crucial requirement for proper management of the Zanzibar Port.

3. How do the Doppler principle ADCPs work?

Measurement Principle

ADCPs are based on the principle of the Doppler effect. An ADCP transmits acoustic signals, or just sound waves, into the water. These sound waves are reflected by very small particles suspended in the water-like plankton, sediment, or even bubbles. When these particles are moving along with the current, the frequency of the reflected sound waves is changed. This change in frequency is the so-called Doppler shift and is measured by the ADCP.

ADCP Applications in Zanzibar Port

Ship - borne ADCP: Ship-borne ADCPs are installed in Zanzibar Port for big-scale surveys in the port area and its surrounding waters. They can be fitted out on vessels, which could map out the current patterns across different areas of the port. It continuously emits and receives acoustic signals while the ship is in motion, thus providing a detailed picture of the current profiles at various depths along the path traveled by the ship. This information can be built into an extensive map of current conditions around the port for navigation planning and possibly for environmental monitoring.

Fixed ADCP: Fixed ADCPs are installed on the seabed or other fixed structures in the port. They are thus used in monitoring long-term current conditions at specific locations. For instance, a fixed ADCP can be set near a berth or in a channel to make continuous measurements of the speed and direction of the current. Such information is quite useful in understanding the day-to-day as well as the seasonal variations in the patterns of currents, which can help in optimizing port operations.

4. What is needed for high - quality measurement of Zanzibar Port currents?

Reliability of Material

The casing of the ADCP current profiler used in Zanzibar Port should be made of highly reliable materials. Titanium alloy is an excellent choice for the casing. Titanium alloy has several advantages. It is highly corrosion-resistant, which is essential in the harsh marine environment of the port. Seawater in Zanzibar Port is so salty that less resistant materials will be corroded in a very short time, which may lead to equipment failure.

Titanium alloy also has high strength-to-weight ratio, which means the mechanical stresses during installation and operation can be withstood while being relatively lightweight. This makes it easier to handle and install, whether it's a ship-borne or fixed-mount ADCP.

Besides, there is a very low magnetic permeability exhibited by the use of titanium alloy, which is advantageous to the ADCP since it does not allow interference of the internal magnetic sensors. Further, this serves to ensure true current measurement: magnetic interference does distort data recorded by an ADCP flow meter.

Size, Weight, and Power Consumption

Smaller in size and lighter in weight: Because of its compact design, the ADCP would be easier to install on ships, especially the smaller vessels normally used for local surveys in the port. It also reduces the load on an installation structure that could be the ship's hull or a seabed-mounted frame. The other important factor is low power consumption. In fixed-mounted ADCPs, they may have to operate for extensive periods of time when access to power supplies may not be easy. The low power consumption ADCPs can be operated on batteries for longer durations and thus avoid frequent replacement of batteries or being connected through complex power supply networks.

Cost-effectiveness

The cost of the ADCP, however, is a consideration factor for large-scale deployment in Zanzibar Port. This is very cost-effective to enable numerous installations for comprehensive monitoring of current conditions within the port. More importantly, such low-cost devices will make them more feasible to be invested in by local research institutions and port authorities that have budgetary constraints with regard to current measurement equipment.

5. How to select appropriate equipment to measure current?

Based on Purpose of Use

• Ship-borne ADCP: If the goal is to undertake large-scale surveys of the port and surrounding waters, then one should use the ship-borne ADCP. It covers the area over a wide range and can present current conditions in each different area in one snapshot for the whole of the port. For example, in order to map the overall current patterns for navigational purposes, a ship-borne ADCP may be installed on a dedicated survey vessel.
• Bottom-mounted ADCP: Long-term monitoring of fixed locations in a port, such as near a critical berth or in a narrow channel, is better served with a bottom-mounted ADCP. This unit can record the current data continuously at one point and obtain valuable information on the local current variations over time.
• Buoy-mounted ADCP: Buoy-mounted ADCPs shall be helpful in the measurement of surface-level current conditions in a port. They can serve to monitor the current at the water-air interface, which is important in understanding the interaction between the atmosphere and ocean in the port area.

Based on Water Depth

• 600kHz ADCP: This frequency works best with water depths not exceeding 70 meters. In Zanzibar Port, some areas are characterized by shallow waters; therefore, an ADCP working on this frequency is ideal for accurate measurement of the current profile in those shallow regions.
• 300kHz ADCP: Shall be better for waters with a depth of approximately 110 meters. It offers better penetration in the water column, with an acceptable level of accuracy in the measurement of the current.
• 75 kHz ADCP: This should be used in areas with water depths of up to 1000 meters, found in some open ocean areas off the Zanzibar Port.

It has a longer range and can effectively measure current in deeper waters. Some of the well-known ADCP brands in the market include Teledyne RDI, Nortek, and Sontek. However, for those looking for a cost-effective yet high-quality option, the China Sonar PandaADCP is worth considering. The all-titanium alloy construction makes it highly durable and very effective. With its incredible cost-performance ratio, it is a great choice for Zanzibar Port's current-measurement needs. For more information, visit https://china-sonar.com.

Here is a table with some well known ADCP instrument brands and models.