Nigerian Dredging Activities in Perspective
- A Feature Article.
By Engr. Emma
With the recent revolution in the indigenous dredging
industry and the associated mass exodus, recent survey has shown that
many firms and investors have entered the industry with little or no
requisite knowledge and expertise. This has led to heavy loss in terms
of finance, capital, man hours and reputation. To reduce this growing
disturbing trend and to prepare and empower dredging professionals and
new entrepreneurs who intend to invest into dredging as an investment
stream, a discourse of this nature is being written to cater for issues
associated with handling and managing dredging projects.
The discourse will be in series featuring: basic knowledge
of dredging and dredging types; dredging equipments and accessories;
dredging projects and types; site dredging personnel and their roles;
basic material requirements for dredging projects; preliminary site
requirements in terms of site inspection and geotechnical/hydrographic
surveys; basic tips on costing of dredging projects; elements of packaging
dredging contract; site management documentation etc. This first series
will consider understanding dredging, dredging areas and associated
What Is The Term Dredging?
Dredging is defined as the removal of soil from the marine environment
and subsequent transportation to another place either for deepening
of water or profitability uses of the soil. In other words, it involves
repositioning of soil from a marine environment, using specialized equipment,
in order to initiate infrastructural and/or ecological improvements.
In this definition "repositioning" stands for the process
of (1) removal, (2) transport, (3) placement and often (4) treatment
of soil; "soil" stands for sediment or silt, as well as for
specified soil types like sand, gravel and rock.
Definitions of dredging usually emphasize the excavation and removal
aspects, because originally the almost exclusive purpose of dredging
was the deepening or widening of silted waterways and harbors in order
to improve navigation ("maintenance dredging") or the creation
of new waterways like the Suez and Panama canals ("capital dredging").
In the 1980's and early 1990's definitions of dredging started to include
the removal of contaminated sediments from marine environments ("remedial
dredging"), as this became an important additional function of
At the end of the 20th and the early 21st century, following a technical
revolution in the dredging industry, large land reclamation projects
(for instance: the creation of artificial islands) were initiated. Today's
definition of dredging therefore speaks of the "repositioning of
soil" and not just of the "excavation of soil". In this
context dredged material is seen as a reusable resource.
The Major Economic Benefits for Dredging
1) Maintenance and expansion (deepening and widening)
of silted water ways and harbors for navigational and transportation
purposes to enhance the growing world trade
2) Flood control and associated coastal protection
due to climate change: The recent flood incident that occurred in Nigeria
where many coastal states were submerged is an instance: This was due
to absence of large scale dredging activities that would have led to
repositioning of silted soil from the channels and creeks as against
upsurge from the sea and since there was no basin to accommodate the
effect of the upsurge, hence the unexpected situation.
3) For the exponential growth in urbanization and industrial
expansion, there is a high demand for new land development hence leading
to large land reclamation projects, e.g. waterfront development and
the construction of artificial islands for airport etc as seen in Dubai
and Lagos (Eco Atlantic).
4) The growth in energy consumption worldwide has led
to dredging projects related to offshore farms, submarine oil and gas
pipeline crossings, and offshore drilling platforms
5) Dredging for beach replenishment and construction
of marinas and deep water cruise harbors for the purposes of water related
tourism (cruises, yachting and beach vacations).
6) Remediation of contaminated sediments, water ways
and habitat restoration leading to the growing need for ‘’
green’’ dredging solutions for sustainable development is
also another important benefit
7) Finally, dredging for mining for the recovery of
minerals, gems and precious metals etc
Different Areas of Dredging Projects
These include capital dredging, maintenance dredging, land reclamation,
sand stock piling, beach replenishment, sub marine pipe/cable line crossing,
rock dredging, contaminant remediation.
Capital: Dredging for creation of new slots, channel, harbor and berth
or deepening of existing facilities (jetty) in order to provide access
for larger vessels.
Maintenance: It involves maintaining navigable silted waterways which
probably become shallower for navigation due to sediments, debris and
mud etc. In other words, this involves dredging to increase the depths
and widths of previously dredged slots and/or access canals, harbors,
ramps, and jetties so as to permit access to a drilling barge or a work
over unit or a supply vessel as may be appropriate.
Land Reclamation: This involves hydraulic sand filling in swampy areas
adjoining creeks and rivers, estuarine coastlines and built up or urban
areas or for the stockpiling of sand. The reclaimed areas will later
be used as sites for land drilling locations and access roads or construction
sites for residential houses, flow stations, harbor works, gas plants
workshops, or offices.
Reclamation operation in progress
Stock Piling: This involves dredging and piling of sand in a dumpsite
for commercial purposes. It may require the deployment of dry plants
like bulldozer, excavator, pay loaders and tipping trucks to site etc
Stock piling operation in progress
Beach Replenishment: Due to erosion of sand by storms or wave action
from the beach, sand is mined offshore and place on a beach to replace
the eroded sand: Trailing suction hopper is mostly used for this operation.
This is done to enhance the recreational and protective function of
the beaches, which can be eroded by human activity or by storms.
Rock Dredging: Blasting is carried out prior to the deployment of a
dredger. However, in recent years, dredgers with more powerful cutters
have been built in order to excavate harder and harder rock without
Rock (quay) dredging process
Pipe/Cable line River crossing: This involves excavation and creation
of trench for pipe/cable line across the sea/river.
Pipeline River crossing operations
Contaminant remediation: To reclaim and remediate areas affected by
chemical spills, storm water surges (with urban runoff), and other soil
contaminations. Disposal becomes a proportionally large factor in these
Types of Dredgers
These include plain suction, cutter suction, trailing suction, auger
(wheel) suction, bucket ladder,
backhoe/dipper and grab dredger.
Plain Suction: It sucks materials through long pipe in form of vacuum
cleaners. It has no cutter at the suction inlet. Jet pumps are commonly
Trailing suction: A trailing suction hopper dredger (TSHD) trails its
suction pipe when working, and loads the dredge spoil into one or more
hoppers in the vessel. When the hoppers are full the TSHD sails to a
disposal area and either dumps the material through doors in the hull
or pumps the material out of the hoppers. Some dredges also self-offload
using drag buckets and conveyors.
Trailing Suction Hopper Dredger
Cutter suction: A cutter-suction dredger's (CSD) suction tube has a
cutter head at the suction inlet, to loosen the earth and transport
it to the suction mouth. The cutter can also be used for hard surface
materials like gravel or rock. The dredged soil is usually sucked up
by a wear resistant centrifugal pump and discharged through a pipe line
or to a barge
Cutter suction dredger
Auger (Wheel) suction: The dredger resembles cutter dredger, but the
cutting tool is not like the common cutter for cutter dredgers rather
it is a rotating set of screw at right angles to the suction mouth.
It is not common in this part of African continent.
Bucket Ladder: A bucket dredger is a dredger equipped with a bucket
dredge, which is a device that picks up sediment by mechanical means,
often with many circulating buckets attached to a wheel or chain. Some
bucket dredgers and grab dredgers are powerful enough to work through
coral reefs to make a shipping channel.
A Grab Dredger: A grab dredger picks up seabed material with a clam
shell grab, which hangs from either an onboard crane or a crane ship,
or is carried by a hydraulic arm, or is mounted like on a dragline.
This technique is often used in excavation of bay mud. Most of these
dredges are crane barges with spuds.
Grab dredging process
Backhoe/dipper: backhoe/dipper dredge has a backhoe
like on some excavators. A crude but usable backhoe dredger can be made
by mounting a land-type backhoe excavator on a pontoon.
Trends in Nigerian Maritime and Dredging Sectors
major focus in this edition is the trend of harbor dredging activities
which are on an upward tick. It is no longer news that the current stock
of river ports in Nigeria are overstretched due to the increase of Nigeria’s
economy and the inadequacy of road and rail infrastructure to cope with
cargo delivery from the quays. In July, the Apapa-Ijora road was blocked
for two straight weeks as all hell was let loose on account of the number
of trucks and trailers jostling for the limited road space. Even though
the Lagos State Government is fast-tracking road reconstructions, albeit
belatedly, there seems to be no solution in the short term.. Read
Other Articles &
Mr Pier Luigi Carrodano on his
work with Gen. T Y Danjuma's companies and the Chinese sea trade with
Engr Akin Olaniyan on need for NIMASA
to return to original mandate and harnessing cabotage trade...NEW
Dr. Wilson Odafe Omene on Niger
Delta politics, amnesty programme, Nigerian maritime and local govt,
Adeyemo on River Niger Dredging...
P.C. Nwilo on his assessment of NIWA during sabbatical ...
Nseyeng Ebong on his 8-year tenure as rector of Maritime Academy
of Nigeria Oron...
Dumo Lulu Briggs as
chairman of Maritime Academy of Nigeria Oron, his vision...
Muyiwa Omasebi: The face-off Between NIWA, MMSD and Lagos State Govt.
K Folarin: The Collapse
of Nig. shipping lines.
Carrodano: How govt
can revive Nig. shipping lines.
Epia: The struggles
of Nig shipping lines with cargo reservation scheme.
Gibb: Intricacies of
the equipment market in Nigeria.
many choppers has DPR got?" - Chief Ogunsiji.
Dredging the Niger Delta: Interview of Ben Efekarurhobo.
of Surveying in the Dredging Industry
Of Myth, Reality and Resource Control
Law: A judgment on the ownership of a sand dredging site by the
Court of Appeal.
Lagos State Attorney General Interpretes state law on sand dredging
NIWA public notice on Lagos State intervention in inland waterways regulation.
Extract Of The Law To Provide For The Regulation Of Waterfront Infrastructure
Development In Lagos State.