THE GREAT WALL OF LAGOS
Eko Atlantic City
By: Colin Seckington, Project Manager at Royal HaskoningDHV
Reclaiming over 10km2 from the Atlantic Ocean to form the foundation upon which the new Eko Atlantic City
will be located has presented Royal HaskoningDHV together with their Client South Energyx Nigeria Ltd
(SENL) with many technical challenges. This 8 year long reclamation project takes place on the south coast
of Nigeria to provide an extension to the former capital and the expanding business district in Victoria Island,
Lagos.
Initially Royal HaskoningDHV were involved in the feasibility study in 2004 to come up with a sustainable
and permanent solution to the strong coastal erosion that had been afflicting the coastal area on the eastern
side of the entrance to the Port of Lagos. This had been taking place for over one hundred years since the
construction of the Lagos harbour moles and for which no adequate solution had to date been found.
Following extensive discussions with SENL it was concluded that it would be more appropriate not to
construct a protective sea wall where the sea had advanced to, but rather to construct a sea defence
structure on the line of the original coastline, as it was in 1905 prior to the construction of the moles. Royal
HaskoningDHV proposed a natural layout of the sea defence revetment and sand filling that would follow the
modern design philosophy for sustainable coastal rehabilitation and embrace the Dutch principle of “building
with nature”. This design philosophy was developed over the last several decades and has been
successfully applied recently on a large scale around the globe. The method implies that coastline
corrections or adoptions follow the historical trends as much as possible, taking into account the influence of
the present man-made situation, in this particular case the Lagos harbour moles.
It was from these humble beginnings that the idea of the Eko Atlantic City was born. The concept would
solve a multiplicity of problems not least the chronic land shortage of Victoria Island, Lagos with its ever
increasing population but also give a sustainable and permanent solution to coastal erosion.
To achieve this would in the end entail having to design and later construct the “Great Wall of Lagos” an
8.4km long sea defence revetment in the Atlantic ocean that would have to withstand the treacherous sea
conditions, caused by the long swell waves, generated from storms in the southern part of the Atlantic; this in
addition to having to retain in excess of 90 million cubic metres of reclamation sand fill which would form the
foundation for the new city.
Following the initial feasibility studies, SENL concluded a concession agreement with the Lagos State
Government for the execution of the project with Royal HaskoningDHV providing consultancy services for
the marine works. The Client was to construct the revetment themselves and employed Dredging
International Services Cyprus Ltd (DI) to supply the sand fill. Royal HaskoningDHV were appointed to design
the revetment and supervise its construction. The design of the revetment was tailored, due to harsh sea
conditions, to allow ease of rock placement using land based equipment only.
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The Great Wall of Lagos - Eko Atlantic City
In order to formulate designs that were appropriate to withstand such harsh conditions, it required imposing
strict design criteria. Design profiles of the sea defence revetment cross sections consisting of a rock core,
secondary rock armour, primary concrete armour unit, a toe berm and scour protection were made for
varying crest heights. The designs underwent rigorous physical model testing in the Danish Hydraulic
Institute in Denmark to investigate the stability and overtopping characteristics of the revetment. Tests were
undertaken in both 2D flumes and 3D basins. The crest level and crest berm of the sea defence revetment
were optimised in satisfying the allowable overtopping criterion. These criteria were set to safeguard the city
from coastal flooding and provide a high comfort and security level and also the hydraulic stability of the
revetment. The revetment has been designed not only as coastal protection but also as an amenity,
providing the foundation for an esplanade and a view across the Atlantic Ocean.
Constructing what ostensibly would become a 18m high structure sitting on the bed of the Atlantic ocean in
sea conditions that at times would be quite hazardous because of these long swell waves has, during the
initial construction stages, presented many technical and logistical challenges and will continue to do so in
the future as construction proceeds.
One of these major challenges on site was to determine an optimum phasing of construction of the
revetment and the sand filling. It became evident at an early stage that delivery of the sand fill should be
carried out from sheltered waters, which implied the optimal usage of the sheltered function of any of the
revetment that had been completed. This would mean that construction of the revetment should run
somewhat ahead of the major sand filling operations, starting from the east harbour mole. However, as
construction of the revetment is dependent on the sand filling to provide access to construction vehicles, it
was necessary to establish a construction front consisting of a small strip of sand filling on the landward side
of the newly constructed section of the revetment. This process would continue over the entire length of a
respective sand filling phase. Following this, major sand filling operations would continue in the fully
sheltered environment on the landward side of the completed sea defence revetment.
Although the above construction methodology is the current modus operandi on site it is a delicate balancing
act fraught with many challenges. The sea defence revetment is not an autonomous breakwater structure,
as it is necessary for protection of the sand fill slope, which makes both the delivery of the sand filling and
construction of the sea defence revetment highly interrelated.
This remains one of the biggest challenges on site, to proceed with the construction of the sea defence
revetment as fast as possible to protect the sand fill area, but at the same time balance this with protecting
the temporary works of the revetment with secondary and primary armour to form the permanent works. The
temporary works therefore proceed only 50 m ahead of the construction of the permanent works of the
revetment.
To date over 46 million m3 of material has now been reclaimed and deposited in the area of the new Eko
Atlantic city, resulting in an equivalent area of over 5 million m2 of land 2m above chart datum and a sea
defence revetment 3.8km long.
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The Great Wall of Lagos - Eko Atlantic City
Photo 1 - The Great Wall of Lagos at 3km length
Photo 2 - April 2012 aerial view of land reclamation
Photo 3 - 3D isometric view of The Great Wall of
Lagos
Photo 4 - Components of The Great Wall of Lagos
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