Design of Marine Protection Works for New
Container Terminal in Karachi, Pakistan
Steve Hinton Project Director, Royal HaskoningDHV, London, UK
Farooque Chaudhry Local Project Director, Techno Consult, Karachi, Pakistan
Mark Hill Project Manager, Royal HaskoningDHV, London, UK
Alec Sleigh Technical Director, Royal HaskoningDHV, Peterborough, UK
Siong Hong Ting Design Engineer, Royal HaskoningDHV, Peterborough, UK
Summary
This paper is a case study covering the planning and design of the marine protection works
(breakwaters) for a new container terminal in Karachi, Pakistan for the Karachi Port Trust. The paper
concentrates on the development of the plan layout for the breakwaters and the cross-sectional
design of these structures.
Introduction
In 2006, Karachi Port Trust (KPT) commissioned a team led by Royal Haskoning (now Royal
HaskoningDHV (RHDHV)) to carry out the planning, design and contractor procurement for the
construction of a new state-of-the-art deep water container port at Keamari Groyne, which is situated
to the south and at the approaches to Karachi Harbour, Pakistan (see Figure 1). The port is to
accommodate container vessels up to 400m LOA (length overall) with a draft of 16m and a capacity of
approximately 13,500 TEU (twenty-foot equivalent unit).
RHDHV was responsible for management of the overall project including contractor procurement and
supervision of the site investigation, masterplanning the port, preliminary and detailed design of the
dredging, reclamation and marine protection works (breakwaters) and contractor procurement for the
dredging and reclamation and marine protection works construction contracts. RHDHV also assisted
KPT with the award of a concession contract for the provision of buildings, services, container
handling equipment and operation for the first phase of the terminal. The concession was awarded to
Hutchinson Port Holdings (HPH) in 2008 and the new facility is to be known as South Asia Pakistan
Terminals (SAPT).
Sub-consultants to RHDHV included Scott Wilson (now URS), HR Wallingford (HRW) and TechnoConsult International (TCI). URS contributed to the terminal masterplan and were responsible for
preliminary and detailed design of the quay wall and contractor procurement for the quay wall
construction contract. HRW was responsible for carrying out hydraulic modelling studies used for
design of the marine protection works and real-time navigation studies which were carried out in
consultation with the KPT Port pilots. TCI, who are based in Karachi, were initially responsible for coordinating and supervising the site investigations and surveys which were carried out by specialist
sub-contractors and throughout the duration of the project contributed to the design and contractor
procurement processes.
The masterplan required the capacity for this port extension to be able to accommodate up to 10
berths in the future; however, Phase 1 is for the delivery of the first 4 berths, comprising 1.5km of
quay wall, together with 75ha of container stacking yard to cater for a throughput of 3 million
containers per year. Phase 1 also included over 30,000,000m3 of dredging, 4,500,000m3 of
reclamation, over 5,000,000m3 of material stockpiled for use in the future development of the port,
with the remainder of the dredged arisings dumped at sea, and 4.6km of marine protection works
(breakwaters and armoured revetments). The breakwaters provide shelter and calm conditions for
safe navigation of the container vessels in and out of the port and the armoured revetments contain
the reclamation material which forms the container stacking yard.
Following on from the design phase, RHDHV, along with TCI, are now carrying out the construction
supervision for the dredging, reclamation and marine protection works construction contracts which
are currently on-going and due to be complete in late 2013.
The paper discusses the planning and design of the marine protection works. The design of these
works was independently reviewed by Baird and Associates.
N
Figure 1: Location plan
Wave Conditions at Site
Weather conditions at the site are dominated by the two monsoon seasons. The south west (SW)
monsoon which occurs in the summer months between May and September and is associated with
hot and humid weather, heavy rainfall and strong and persistent winds which generate swell waves
with long periods (12 seconds and above). These swell waves approach Karachi from the SW. The
north east monsoon occurs in the winter months between December and February and brings some
relief from the weather conditions that persist during the summer monsoon. The wave conditions at
Karachi during the winter monsoon are also modified.
Cyclones occur in the Arabian Sea during the SW monsoon season; however, a review of historical
tracks has shown that there is no record of a cyclone hitting the city. Karachi does, however, suffer
from the effects of passing cyclones and experiences strong winds, rough seas and swell and
torrential rain.
Layout of Breakwaters
Initial Layout
Following the decision to develop a new port to the east of Keamari Groyne, studies were completed
to develop a layout of breakwaters that would provide acceptable wave conditions at the new berths
and in the approach to the entrance. The final layout is provided in Figure 4; however, this section
describes how this layout was developed.
Initial layouts looked at the retention of the existing Manora Breakwater as the primary defence
against the monsoon swell with a secondary structure (Keamari Breakwater) extending the existing
Keamari Groyne to the south east by approximately 600m. The latter structure was to protect the new
basin from swell passing the end of the existing Manora Breakwater. The layout also included the
construction of a 2,800m long lee breakwater (Oyster Rocks Breakwater) to protect the basin from
locally generated waves from the south east and to also prevent the migration of sediment from the
Clifton foreshore into the new berths.
This layout was tested by HRW in their wave penetration model, ARTEMIS and the results for a 1
year wave from 210° and 240°N are shown in Figure 2.
Figure 2: Initial layout - 1 year waves
The modelling indicated good conditions at the berths with wave heights less than 0.5m under a 1
year return period storm. However, conditions were a concern in the final length of the approach
channel, at the confluence of the existing Lower Harbour and in the channel into the new port, where
the modelling indicated wave heights up to 2.5m. This raised concerns over whether or not wave
conditions were calm enough to allow tugs to be made fast to vessels entering the port (to help
control navigation) and whether or not the vessel could reduce speed sufficiently and still maintain
steerage into the new port. It was also important to ensure that the incoming vessel had sufficient
distance to reduce speed and stop at the manoeuvring basin, located at the northern end of the port
basin.
Alternative Layout
From these initial tests it was apparent that whilst the layout of the breakwaters provided acceptable
conditions at the berths, changes were required to provide acceptable conditions in the navigation
channel. An alternative layout was developed which extended the existing Manora Breakwater so
that the roundhead was positioned close to the navigation channel. The Keamari Breakwater was
removed from the layout because of the additional protection provided by the extended Manora
Breakwater. Two variations to this layout were tested by HRW in their ARTEMIS model; one with the
roundhead next to the channel and a second with the roundhead located 150m back from the
channel. The results are illustrated in Figure 3 for 240°N.
The figure indicates that extending the Manora Breakwater significantly improved wave conditions in
the final length of the approach channel and further fast time simulations demonstrated that vessels
would be able to safely enter and exit the harbour. With the wave height reduced to 1 to 1.5m, it
would be possible to attach tugs to the vessels in the area behind the new breakwater. The modelling
also demonstrated that the conditions were sensitive to the location of the roundhead and it was
concluded that it should be located as close as possible to the channel.
The extension of the Manora Breakwater also significantly improved wave conditions in the Lower
Harbour (see Figures 2 and 3) which will be a benefit for the whole of Karachi Harbour.
The wave penetration modelling has shown that the side slopes of the deep dredged channel into the
port are, in part, responsible for the good wave conditions at the berths. The side slopes refract
energy away from the channel (see Figure 3) and reduce the height of waves that enter the basin.
This process, however, resulted in a concentration of energy along the west side of the channel and a
focussing of waves towards the southern corner of the quay wall. There were concerns that this
focussing of waves could result in poor conditions on the most southerly berth and a decision was
taken to introduce a short stub breakwater to stop this energy entering the basin. This focussing of
energy is shown in Figure 3 together with the short length of breakwater (Keamari Breakwater).
Longer Breakwater
Figure 3: Alternative layouts – 1 year waves
Shorter Breakwater
Final Layout
The final layout for the new container terminal is shown in Figure 4. The marine works comprise the
1,100m long New Manora Breakwater, the 2,500m long Oyster Rocks Breakwater and the 300m long
Keamari Breakwater. In addition, the works comprise the 700m long Keamari Revetment which is an
extension of the Keamari Groyne and protects the reclamation fill for the new container yard.
Figure 4: Final layout
The final layout was verified using real-time navigation modelling which was also undertaken at HRW
with the Karachi Port Pilots in attendance. Following this exercise, minor modifications were made to
the dredging layout but the breakwater layout remained unchanged.
Existing Manora Breakwater
The existing Manora Breakwater and Keamari Groyne were constructed at the end of the nineteenth
century (in the 1870’s) to train the flows into and out of the natural harbour at Karachi and so improve
the depth of water over the entrance bar. The breakwater was additionally designed to protect the
entrance to the harbour from swells during the SW monsoon and, with the groyne, to also control the
movement of sediment from the adjacent foreshores.
As originally constructed the Manora Breakwater consisted of large concrete blocks weighing
approximately 27t placed on a rubble mound foundation. Since completion, settlement has been an
on-going problem and has resulted in the movement of the blocks. As a consequence the crest has
been raised on a number of occasions by the addition of a reinforced capping. In 1968 the
breakwater was strengthened with 28t, 14t and 7t concrete cubes placed in Pell-Mell fashion so
effectively converting the vertical breakwater into a rubble mound structure. The current structure is
illustrated in Figure 5.
RC Capping Concrete Cubes
Concrete Blocks
Figure 5: Existing Manora Breakwater
Once the layout of the marine protection works had been finalised a decision had to be made over the
future of the existing Manora Breakwater. There was the option to improve and extend the existing
structure or to construct a new breakwater alongside.
The ongoing settlement of the existing structure was a concern. Although not fully understood,
investigations suggested that it was a result of internal instability with the loss of small rock from the
mound and underlying fill rather than poor ground conditions. This together with the risk of voids
under the capping due to movements of the blocks meant that if the new breakwater was to be
constructed over the existing then it would have been necessary to dismantle much of the structure to
provide internal stability between the rock layers and ensure voids were not encapsulated into the
structure. It was, therefore, concluded that it would be preferable to construct a new breakwater
alongside the existing structure.
Design of New Structures
Design Conditions
Offshore wave data was obtained from the UK Met Office global wave model and the data base of
Voluntary Observations from Ships (VOS). These data sets were extrapolated to give extreme
offshore wave predictions. It was found that the VOS extreme predictions were considerably more
severe than the Met Office model. This was considered in part due to the length of the model data
record (5 years) and that the model would not adequately resolve tropical storms. The VOS
predications were, therefore, adopted for the design conditions and transformed inshore by HRW
using their TOMAWAC model. Design significant wave heights at the New Manora Breakwater were
up to 6m.
A detailed assessment of design wave heights along the New Manora and Oyster Rocks Breakwaters
was undertaken using the results from the TOMAWAC and ARTEMIS models. This allowed armour
sizes and crest levels to be optimised over the length of these structures.
Design water levels were based on historical records for Karachi and led to the adoption of a level of
+4.15m Port Datum (PD) which included an allowance for storm surge and sea level rise.
Development of Cross-section
The development of the breakwater cross-section and subsequent detailing of the structures followed
recognised coastal engineering practise and guidance set out in documents such as BS 6349 i, The
Rock Manual ii and the Coastal Engineering Manual iii. Aspects of the design are discussed below.
Selection of Crest Detail
One aspect that influenced the design of the structures was the decision to adopt a cross-section
comprising a simple mound with no crown wall or roadway. This was possible as port operations will
not take place immediately in the lee of the three breakwaters which meant that it was not necessary
to apply strict operational limits on wave overtopping. Following discussions with KPT it was decided
that a cost effective cross-section with a relatively low crest and without the inclusion of a costly wave
wall should be adopted. This decision, however, meant that the roundhead navigation beacons would
have to be located on free-standing steel structures located adjacent to the roundheads.
Selection of Primary Armour
The wave conditions at the outer lengths of the structures meant that concrete units were needed for
the primary protection. A decision was taken to adopt single layer units because of the savings that
could be achieved in the volume of concrete required and the steeper slopes that could be adopted.
The latter leading to savings in the volume of rock in the core. In practice a slope of 1 in 1.5 had to be
used (rather 1 in 1.33) to achieve geotechnical stability under seismic loadings.
Single layer units rely on careful placing to achieve good interlock and this raised some concerns over
the work that could be completed during the SW monsoon. It was concluded that placing armour units
(and potentially also rock placing) would have to be suspended on the exposed New Manora
Breakwater during the monsoon season but that there was sufficient work in the more sheltered
locations of the site to allow the efficient construction of the marine protection works. It was,
therefore, concluded that any programming issues were outweighed by the savings available from the
use of single layer armour.
Core-LocTM units were selected as primary armour on all three breakwaters because of their good
hydraulic characteristics which meant that they were also cost effective. Three sizes were used in the
design: 20t (8.5m3), 14.6t (6.2m3) and 5.6t (2.4m3).
The less exposed lengths of the breakwaters were armoured with rock using a maximum weight of
1.5t following investigations into the likely size that could be consistently produced by local quarries.
Larger 3t, 4t and 5t rock was used selectively as toe armour.
Crest Levels and Widths
A limit of 100 to 200 l/s/m was initially set for overtopping of the structures under the design wave
conditions and the required crest levels calculated. This led to roundhead crest levels of +9.0m PD on
the New Manora Breakwater and +7.5m PD on the Oyster Rocks Breakwater. The levels were
confirmed during the physical model tests (see later) when the limits on overtopping were based on
the stability of crest armour rather than overtopping discharge. A crest width of 10m (equivalent to 6
Core-LocTM units) was adopted for the New Manora Breakwater.
The final design cross-section for the New Manora Breakwater is shown in Figure 6.
Figure 6: Cross-section through trunk of New Manora Breakwater
Design of Roundheads
The existing sea bed at the entrance to the port is relatively shallow (typically -10m PD) with rock
close to the surface. This necessitated dredging a deep channel through the entrance to achieve the
required navigation depth of -16.0m PD.
Figure 7: Cross-section through roundhead of New Manora Breakwater
The presence of rock complicated the design of the roundheads as there were concerns over the
geotechnical stability of the structures if placed close to the 6m high slope into the channel. This left a
choice between either pulling the roundheads back from the edge of the channel or lowering the
founding level so that it was closer to the dredged channel level. The latter approach was adopted
based on the results of the modelling which indicated the wave conditions in the channel and basin
were sensitive to the length of the breakwater. A typical cross-section through the New Manora
Breakwater roundhead is shown in Figure 7.
Access to Navigation Aids on Roundheads
As noted earlier a decision was taken in the early stages of the design to place the roundhead
beacons for the breakwaters on free-standing steel structures. However, a late decision to place the
beacons on the roundheads left a problem of access for maintenance.
Enquiries, including contact with Concrete Layer Innovations (CLI); the developers of the Core-LocTM
units, were made to see if any innovative methods had been devised for providing access onto the
crest. This led to discussions with a port in Argentina where a ladder arrangement had been placed
over the surface of the concrete units and tied to individual units. However, from the discussions with
the port, it appeared that this solution was not successful and had been abandoned.
In the absence of a suitable detail a set of access steps was developed using large mass concrete
blocks. The step blocks were located in the lee of the roundhead away from direct wave attack and
placed onto the underlayer with Core-LocTM units laid against the blocks. The base of the steps was
supported on an extended toe berm. The access steps are shown in Figure 8.
Figure 8: Stepped access onto Keamari Breakwater
Confirmation with Physical Modelling
2D and 3D physical model tests of the New Manora Breakwater were completed at HRW to confirm
the stability of the Core-LocTM units and the overtopping characteristics of the breakwater.
The modelling indicated that the selected units were stable under the design conditions but that some
rocking and settlement occurred under overload conditions. A decision was, therefore, taken to
increase the size of the units on the New Manora Breakwater as this structure would be exposed to
persistent and harsh wave conditions during the SW monsoon when, for a period of approximately 5
months per year, it would not be possible to undertake any repairs.
In addition to the assessing the performance of the New Manora Breakwater, the results from the
stability and overtopping tests were used to calibrate the design equations used to assess armour
size and overtopping on the Keamari and Oyster Rocks Breakwaters. For armour stability this
involved comparing the Core-LocTM stability coefficients from the modelling with those published by
the developers and, for overtopping, fitting curves to the model results. This work led to some final
optimisation of armour sizes and crest levels on these structures.
Construction of Marine Protection Works
A marine works construction contract was awarded to China Harbour Engineering Company (CHEC)
and works commenced on site in early 2010. The works are now (January 2013) nearing completion
which is scheduled for late 2013. Two photographs illustrating the construction of the New Manora
Breakwater are provided in Figure 9.
Placing Underlayer rock
Placing Core-LocTM Units
Figure 9: Construction of New Manora Breakwater
Concluding Remarks
The conditions during the SW monsoon have made the planning, design and construction of the
marine protection works for the new container terminal at Karachi a challenge. The conditions meant
that in planning the layout of the breakwaters careful consideration had to be given to both navigation
issues and wave protection at the berths. The project has shown that developing the layout of the
breakwaters is an iterative process and for this to be done efficiently requires the navigation and wave
penetration studies to be undertaken in parallel.
With the marine works comprising three separate structures totalling 4.6km in length it was not
practicable to test representative cross-sections from all three structures in a physical model.
Nevertheless, the project has shown the value of physical modelling in not only refining the design of
the tested cross-section but also in using the model results to “calibrate” the design formula for the
specific conditions at the site. This allowed refinement / optimisation of the structures which was an
important aspect during the design of these long structures.
It is considered that the steps developed to gain access to the roundhead provide a solution that
could be used on other breakwaters where there is no overriding requirement for access along the
crest. The approach can lead to considerable savings, particularly on long structures. It should be
noted on the Karachi project a decision was taken not to introduce the steps on the roundhead of the
New Manora Breakwater because of the wave exposure and the potential for the development of high
pressures behind the step blocks. It was considered that the stability of the blocks and adjacent
armour units would need to be tested in a physical model before adopting the steps on this exposed
structure. Nevertheless, the detail has potential applications for other projects.
Finally the authors would like to thank the Karachi Port Trust who generously gave permission for this
paper to be published.
i
British Standards Institution (1991). BS 6349-7, Maritime structures- Part 7: Guide to the design and
construction of breakwaters. BSI, London
ii
CIRIA, CUR, CETMEF (2007). The Rock Manual. The use of rock in hydraulic engineering (2nd
edition). C683, CIRIA, London.
iii
US Army Corps of Engineers (2002). Coastal Engineering Manual, Engineer Manual (EM) 1110-21100. US Army Corps of Engineers, Washington, D.C.