Dr. Michel A. Thomet
Manager of Facilities Simulation
2014 World Congress PIANC
San Francisco, USA
Gabon is a rapidly developing country in West Africa which is undertaking the expansion of Port Gentil into a major multi service facility supporting the oil and mining industries. The major driver of the current expansion is a proposal to link the port to the rich iron ore deposits located in the interior of the country via a new rail line. This presentation summarizes the planning and design work prepared by Bechtel and other consultants to analyze and design the port and rail development.
Unlike many of the ports in West Africa, Port Gentil has deep water close to shore and it is relatively sheltered from ocean swells, behind Cape Lopez. Its main disadvantage is having no land links to the rest of the country, which isolates it and makes access difficult. At present, it is used mostly to export limited amounts of crude oil.
The country has an ambitious development plan, laid out in an economic vision for the country introduced and supported by the government. As part of the vision, Port Gentil will be playing an important role and grow much beyond its present size. New berths will be built to serve Capesize ore carriers that will export the ore from the large inland mine deposits.
The iron ore movement will be made possible by a new 650 km rail link connecting Port Gentil with the interior of the country. A new road link will also be built to further integrate Port Gentil with the rest of the country. As a value adding economic effort, some of the iron ore will be used locally in a mini steel mill located in a special economic zone at the port. The commercial port facilities will also need to be expanded with more general freight berths, a Roro berth, and some container berths, as the new land links will enable Port Gentil to supply the multi-modal needs of the country.
Lastly, because of its deep water access, Port Gentil could also become a trans-shipment hub, serving the adjacent African countries of Cameroon and The Congo. It would be able to receive and process efficiently large containerships in the 4,000+ TEU class.
Port Gentil is the second largest city of Gabon with 140,000 inhabitants. It is on an island – the île Mandji – in the delta of the Ogooué river. As of today, it does not have land links to the rest of the country. It is served by an international airport and can also be accessed by a fast ferry from Libreville and a riverboat from Lambaréné.
The city’s vocation is to serve the oil industry of Gabon. It has many offices for several large oil companies that operate in Gabon. It has an oil port for the export of crude and the import of other petroleum products needed in the country. It has a refinery to cover some of the country’s need in refined products. Butane is also produced and is bottled and distributed throughout the country for cooking needs.
The existing commercial/industrial port of Port Gentil, covers the general needs of the city and is also used to support the operation of the offshore oil platforms. The old port – Port Môle - is used by the passenger ferries and the riverboats, as well as by fisherman. There is also a wood port which exported the logs that were floated down the Ogooué river. A law recently enacted, prohibits the export of logs as such. The logs have to undergo at least a first level of in-country transformation before the wood can be exported.
To help foster the development and growth of Port Gentil, a new Special Economic Zone (ZES) was created by Presidential Decree, north of Port Gentil. Through favorable fiscal and regulatory policies, it is hoped that the ZES will attract foreign as well as Gabonese private investors. Such investments are expected to be downstream industries, complementing the present activities. For instance, using some of the crude oil and natural gas available, a new refinery will be built, together with a fertilizer plant and some petro-chemical plants. If and when iron ore becomes available, a mini-steel plant will be added, producing some of the structural steel and rebars needed domestically. Second and third level wood transformation industries could be included, producing plywood, glue-laminated beams and construction supplies like doors, windows, frames, stairs steps, etc.
This is the most favorable site within 500 km for the establishment of a deep water port, capable of handling Capesize bulk carriers, supertankers and post-Panamax containerships. It is sheltered from the Atlantic swells and within less than 1000 m from the shore, the bottom drops to more than 20 m.
From the Cricri Point (West) to the Chapuis Point (East), a wide sandbar has formed, whose depths vary from 0 m to 2 m. From the Chapuis Point (East) to the sand bank of the Pigeon Island (South-East), the Golf of Nengabembé is very close to the coast, and the depths reach very quickly 25m, while in the Bay of the Prince, depths quickly reach 100m (LAT), after a sandy plateau of a few hundred meters. Such uneven slopes stress the importance that should be paid to the stability of the seabed during the implementation of infrastructure.
Bathymetry of Mandji Site - Bay of Cape Lopez
The climate of Port Gentil is a transitional equatorial climate: warm and humid, it is strongly linked to ocean conditions. Mean monthly temperatures are high throughout the year and range between 23° C and 28° C. Rainfall in the Port Gentil area varies from 1800 mm to 2200 mm/year. The dry months extend from June to August, with monthly rainfall of about 20 mm. From October until May, the monthly rainfall exceeds 100 mm. In addition, in this region the ten-year downpour over a period of 15 minutes can reach about 180 mm / h.
The following extreme wind speeds can be expected, for a sustained 1h wind at 10m altitude and from Southwest:
- Annual Wind: 11m /s
- Ten-year Wind:12m /s
- Hundred-year Wind: 13m / s.
The tide at Port Gentil is of low amplitude and semi-diurnal type. The water levels above the datum point are:
- Average level: +1.23 m
- Maximum High Water Springs: +2.20 m
- Mean High Water Springs: +2.00 m
- Mean Low Water Springs: +0.40 m
- Minimum Low Water Springs: +0.20 m
These levels do not take into account the possible phenomena of atmospheric pressure or concomitant depression, or their long-term evolution by climate change.
According to the BCEOM study (hydrographic report - April 19776), the maximum velocity at 2 m depth is 0.45 m/s for the ebb flow and 0.3 m/s for the flood flow. The ebb current is parallel to the coast, while the flood is perpendicular to the shore.
In November 2012, Egis commissioned a study on large-scale metocean conditions along the Gabonese coast based on a satellite hindcast WaveWatch III and a transfer model SWAN for wave propagation taking into account diffraction, reflection , refraction, shoaling and breaking.
According to the study of GlobOcean (Climate wave off the coast of Gabon), the swells off Mandji Island were in the main directions from South to Southwest. Thus, the site of Mandji is found to be protected from offshore swells, which are refracted and greatly reduced in the east side of the Mandji island.
It appears that the diffraction around Cape Lopez Bay towards the Prince is limited. On the east shore, the significant swells exceed 0.75 m less than 1% of the year. The calculation of the ten-year wave was obtained by BCEOM (Project of a deep water port, hydrographic report) on the basis of observations made between 1972 and 1973. The maximum ten-year waves is Hmax = 2 m with an average period of 6 seconds.
Iron ore trade
Gabon has untapped reserves of iron, estimated at 1 billion tons of in Belinga , in the northeast of the country, with a high content of iron (64%). Other deposits of medium sizes were found in the provinces of Nyanga and Ogooué Lolo. The development of these iron ore deposits is one of the major strategies of the Gabonese Government to diversify its sources of growth.
The various transformations of ore depend on the desired final product, determined both by the project sponsors and potential buyers (from untreated ore to specialty steels, going through ore concentrate, pre-reduced iron pellets, ingots and steel billets).
The Gabonese government has recently awarded to a well known and respected company, the task of establishing the size and quality of the Belinga ore bodies at a world class standards (bankable document). This study is expected to be completed in late 2014. After that study has been completed and endorsed, the government would award a concession to interested bidders. The concession will include the following four components which will be implemented in partnership with the government.
- exploitation of iron ore in Bélinga
- construction of a power plant
- building a railway track
- construction of a deepwater bulk terminal in Port Gentil
Depending on the quantity and quality of the ore established, the exploitation of the mine may last 25 to 30 years or beyond. The initial throughput may be 25 million tons per annum (MTPA). Eventually, this throughput may rise to a level of 100 MTPA.
The construction of the heavy haul rail link from Belinga to Port Gentil is going to require more time than the development of the mine concession and may be completed several years after the start of production at the mine.
In a first phase, the iron ore might be moved on the existing Transgabonese railroad to the port of Owendo and exported on small, sub-optimal bulk carriers. The channel depth to Port Owendo is limited to 13 m and the largest ships that can be served are 70,000 DWT, like those used at present in the trade of manganese concentrate. After the rail link to Port Gentil is completed, as well as the mineral terminal, the iron ore can be exported on larger, more economical bulk carriers (Post-Panamax and Cape-size).
A major new infrastructure needed for the export of the Belinga iron ore is a new heavy haul rail line to Port Gentil, as shown in Figure 4. This line will be about 653 km long and will consist of a single track capable of supporting railcars with a maximum 32 MT axle load. This would allow each railcar to carry up to 100 MT of payload. Additional branches may be added later to exploit other iron ore mines in the Congo or in the Cameroon.
The Belinga mine is at 510 m of elevation and the track from there will go across rolling hills, descending progressively until it reaches the station of Abanga on the existing railway which is at about 50 m. Although the final alignment has not yet been determined, the grades will be kept at a maximum of 0.5% for loaded trains (towards Port Gentil) and 1.0% for empty trains (back to the mine).
From Abanga, the new track will leave the right-of-way of the existing track and head for Port Gentil, across the delta of the Ogooué. One possible alignment is on solid ground through the Wonga Wonge National Park (northern option). If this option should be disallowed by the government, a southern option will avoid the park, but will be on more swampy terrain and will have to cross several arms of the river.
If the line has to have an ultimate capacity of 100 MTPA, the single track should be able to accommodate daily up to 10 trains of 300 railcars each. The basic assumptions are that the trains can operate 340 days a year (leaving 25 days for track maintenance), and have a top operating speed of 70 kph (loaded) and 80 kph (empty). A minimum of 14 passing sidings will be needed, each one capable of accommodating trains of up to 3.3 km in length.
Proposed New Rail Line from Belinga to Port Gentil (Green)
This spacing of the sidings would allow 10 ore trains a day in each direction to be run in 16 hours. Another 5 hours could be used for 3 more trains which could carry general freight and/or passengers. This would leave 3 hours for track maintenance. The trains would take about 11-12 hours for a one-way trip, and including the loading, unloading, fueling and inspection times, the trains could cycle once every 32 hours. Some 4 train sets would be needed to operate at the starting level of 25 MTPA. This number would increase to 15 train sets at the ultimate level of 100 MTPA.
At the mine, the trains would be loaded by moving continuously under a loading tower (0.5 to 1.2 kph). As the empty cars approach the tower, they are weighed and their gross weight is used to determine their payload within 0.5% such that the maximum axle load is not exceeded. The exact quantity of ore is then dropped from the storage bin of the tower into a surge bin. As the car body passes under the chute, a fast door is opened and the car gets filled by the time the end of the car body reaches the chute. After leaving the tower, the cars are weighed again to verify that their axle loads are not exceed and to recalibrate the loading rate for the next cars.
In the port facility, the railcars are unloaded through a rotary dumper. Two cars at a time are pulled in the rotary dumper by the train positionner, and then are rotated upside down after being securely clamped. The cars have special couplers that can rotate around their axis so that the dumping operation can proceed without having to uncouple the railcars. After the iron ore in the railcars is dropped into an underground hopper, the dumper rotates the cars back to their vertical position, unclamps them and the train positionner pulls the next two cars into the dumper. The whole cycle takes about 1.5 minutes to unload two cars (200 MT) which translate into an unloading rate of 8,000 MT per hour. From the underground hopper, the iron ore moves on conveyor belts to the stockyard where one or more stacker/reclaimers drops it on longitudinal pile of up to 15 m in height.
In the Abanga station, the new rail line will connect to the existing line through a Y-junction. This will allow general freight and container trains to go from the commercial port of Port Gentil to Libreville and the rest of the country. Because much larger container ships (liners) could call in Port Gentil than in Owendo, Port Gentil could even become a trans-shipment hub for Gabon and neighboring countries. In addition, Port Gentil could become the main port for Libreville in particular and the rest of the country in general.
Freight trains to Libreville would take 6-7 hours, which is all right for general freight and containers. The trip would add some cost to containers delivered in Libreville, however, it would be more than offset by travelling on larger, more economical containerships to Gabon. Also, with increased traffic and ship sizes, the port of Port Gentil would offer a much larger choice of destinations to prospective shippers. For passengers, a train ride between Libreville and Port Gentil would not be very attractive, considering that even the slowest ferry takes only 4 hours and is likely to be cheaper than the train fare.
Finally, the new rail line might be used by the trains of COMILOG from Moanda to export the manganese ore more economically on larger ships from Port Gentil than from those than call in Owendo today. Other mines that started (manganese in Ndjole) or will soon start (rare earth in Maboumine) their operation would also benefit from exporting their ore through Port Gentil.
Bulk terminal in Port Gentil
The following landside facilities are needed to support train operations, track maintenance, handling and storage of ore, and general administration of the terminal:
For bulk handling
- A rotary dumper
- A open air stockyard
- A sampling tower
- Conveyors belts and transfer towers to move the ore
- Hoppers for buffering the bulk material
- A workshop equipment maintenance
- Three electric substations
For the operation of trains and railway
- A train turnaround loop
- Receiving tracks for holding arriving and departing trains
- Shunting tracks for breaking up trains into rakes suitable for the dumphouse
- A maintenance workshop for railcars and locomotive
- A workshop for track maintenance
- A locomotive refueling and washing station
- A rail traffic control tower
- An electrical sub-station
For the overall operation of the terminal
- Administrative buildings: Harbor Master building; Customs; Terminal operator
- The access roads
- Buildings and facilities for monitoring and control
- A tank farm
- Emergency services
Trains arriving from the Belinga mine will have up to 300 gondola railcars and 3-6 locomotives depending on the power of these units. The locomotives will distribute along the train and remotely controlled from the head locomotives. This is done in very long trains to stabilize the slack action and reduce the maximum stress on the couplers. The receiving tracks will have to be long enough to store a full 3.3 km long train. After arrival, the train will be broken up into 3 one hundred railcars rakes and each rake will be shunted to the dumphouse where the train positionner will process the rake through the dumphouse, two cars at a time. The empty rake will then be pulled by the shunt engine through the rail loop and set on the departing track. In the meantime, the mainline engines will be fueled, washed and inspected.
The stockyard, is dimensioned for a throughput of 25 MTPA. The bulk material is stored in 12 active piles, which corresponds to 18 days of production or 1.5 million MT. Each pile can consist of different products, such as sinter feed or pellets of different composition. Stackers and reclaimers circulate between the piles to drop bulk material from trains or collect it for ship loading. Conveyor belts connect the dumphouse to the piles and from there to the sampling tower and the trestle for ship loading. The layout of the conveyor belts will also enable the direct loading of ships from the dumphouse, while by-passing the stockyard.
When the throughput is increased to 50 MTPA and ultimately to 100 MTPA, the stockyard size will be doubled and quadrupled. These areas will be reserved in the facility layout. A second and third dumphouse will be added and additional tracks going to/from these dumphouses and around the loop will be needed.
Bulk Handling Facilities and Stockyard
Depending on the markets and clients served, different ship sizes can be expected. The fleet mix will include bulk carriers from Panamax size (50-100,000 DWT) to the largest Cape Size (200-250,000 DWT). Their characteristics are summarized in Table 1. To accommodate the largest ships, the mooring area will have to be 23 m deep to ensure operation in all conditions. This area will measure 450 m x 170 m for a single berth. The turning basin will have a diameter of 660 m, but need to be only 12.5 m deep, since it is used only by empty ships (half-ballasted) on their arrival. Loaded ships will sail straight out.
Bulk carrier berths of this size are often made of composite steel and concrete structures, with the following composition:
- Loading platform fully drivable or partly drivable
- Foundations: Grid of steel pipe piles, with sand filling, and concrete in the pile heads to ensure rigidity
- Lower deck: Matrix of standard structural steel or prefabricated concrete beams according to local code
- Upper deck: prefabricated concrete slabs in general,
- Docking structures with dolphins regularly spaced (about every 30m for a Capesize)
- Foundations: Several steel tubular piles, inclined or vertical depending on soil, with sand filling, and concrete in the pile heads to ensure rigidity
- Generally no intermediate structure is needed when berths are not across each other. Otherwise a massive reinforced concrete slab provides an important anchoring of the piles. One or two bollards with automatic decoupling are attached to each berth.
- Connections to limit any transfer of horizontal force to the platform
- Independent docking structures at the ends, connected by pedestrian bridges only on single or multiple dolphins depending on the soil. Double bollard with automatic decoupling.
Table 1: Ship characteristics and fleet mix
|Nominal Ship Size
||75 000 DWT
||180 000 DWT
||250 000 DWT
||179 900 DWT
||89 000 T
||205 000 T
||280 000 T
||205 000 T
|Length Over All (LOA)
|Max Mooring speed (with tugboats)
|Number of holds
|Length of the holds
The trestle must support the following static loads:
- A roadway for vehicle and a maintenance crane of up to 60 MT
- A polar shiploader with a slewing and luffing boom weighing 1200 to 1300 MT
- A 70 m long tripper for the conveyor belt weighing 200 to 600 MT
- A buffering hopper of 1800 m3, weighing up to 5500 MT fully loaded
- A protected conveyor belt along the trestle
- Pipes for fire water, potable water, and dust abatement water
- Electric cables
The trestle for loading up to four iron ore bulk carriers (at 100 MTPA) will be located in the bay adjacent to parcel F of the Special Economic Zone. This is across the existing basin of the crude oil terminal in the “Baie du Prince”. Available depths allow access of the design ship to the maneuvering areas and to dock in any tidal conditions, including in case of a low pressure through. Because the bottom drops rapidly, no dredging is needed, but the end of the trestle will be in 40+ m water, which will present technical difficulties. The advantage of this layout is that the ships will be moored in a direction perpendicular to the waves.
Plan and Elevation of a Typical Trestle with a Roadway
Port facilities layout
The area needed by the stockyard and rail facilities will cover from 95 to 280 ha, depending on the annual volume of ore handled. The whole area is low and subject to flooding and must therefore be raised. This will require about 3 million m3 for the initial development phase. Most of this material can be dredged from the Prince sandbank, which is quite extensive and shallow.
Bulk Terminal Layout
- The project is technically feasible for the export of iron ore from 25 to 100 MTPA, while remaining compatible with existing nearby facilities (Total Gabon crude oil terminal and the airport) as well as plots F and G of the future special economic zone (ZES).
- A long term land commitment of nearly 900 hectares in northern Mandji is required (nearly 200 hectares of land for startup).
- The completion of a heavy rail line from the Mine site of Belinga to Port Gentil is required, which is one of the major challenges of project.
- All the operational needs of the mine can be provided from the Mandji terminal.
- The project is conditioned on the implementation of the infrastructure of the adjacent ZES (power generation, port services , oil terminal, container terminal)
- The project requires (like the ZES) the use of hydraulic fill of sand off the bank of the Prince for achieving the desired level of the platform.
- More than 80 % of the mangrove area can be kept free of any infrastructure.
- For 25 MTPA, one berth at sea - with a polar loader and connected by a trestle on steel piles of about one kilometer – is enough. This berth can accommodate bulk carriers up to 250,000 tonnes of payload
- Calls of ships of less than 100 000 tonnes will have to be avoided in order to achieve the annual targets export.
- A priori, there is no need to build a breakwater
- A 25 MTPA , it is possible to avoid dredging near the coast, and thus preserve the sediment balance and the mangrove intact
- Finally, this project fulfills some of the presidential visions in the “Gabon Emergent” strategy, namely the spreading of the country’s development to other provinces of Gabon in general, and the re-attachment of Port Gentil to the hinterland in particular.
- Etudes des Ports Nationaux, volet 2 – Terminal Minéralier de l’Ile Mandji, Aout 2013, Egis International
- Etude sur les liens alternatifs de transport entre Lambaréné et Port Gentil, Rapport Intermédiaire, BNETD, Septembre 2013
- Plan Stratégique Gabon Emergent, Stratégie Nationale d’Industrialisation, Ministère de l’Industrie et des Mines, République Gabonaise, Juin 2013