Indian Journal of Geo-Marine Sciences
Vol. 39(4), December 2010, pp. 597-604
Impact of port development on the coastline and the need for protection
M D Kudale
Central Water and Power Research Station, Pune 411024, India
[E-mail: [email protected]]
Received 20 August 2010, revised 21 December 2010
Coastal areas are varied in physical features. The coastline shows constantly varying nature due to tidal effects and
seasonal changes in wave and wind climate. Occasional cyclones in the region also have influence on the overall
morphology. It is necessary to understand the coastal processes and predict likely effects before undertaking any coastal
project. Developments of major/minor ports and fishery harbours consist of the construction of coastal structures like
breakwaters, jetties, groynes and reclamation bunds. Developments of the ports also involve the dredging and disposal
activities to maintain the required depths for navigation. These coastal structures and the dredging activities interfere in the
coastal processes of the region. Modifications in the coastal processes have large impact on the coastline. Major
morphological impact is felt in the coastal region having high rate of longshore littoral drift. Accumulation of sediments on
the updrift side and erosion of the downdrift side is inevitable in these regions. Sand bypassing is one of the best solutions to
mitigate this problem. Sand bypassing should form an integral part of any port development project at the planning stage.
[Keywords: Port development, Breakwater, Coastal erosion, Coastal protection, Beach nourishment, Sand bypassing]
Introduction
Construction of the coastal structures and the
dredging activities for the development of ports
interfere in the coastal processes of the region. The
modifications in the coastal processes may have large
impact on the coastline. As such, it is necessary to
understand the coastal processes and predict the likely
effects before undertaking any coastal project. Apart
from the hydraulic studies, some foresight is essential
to avoid undesirable coastal changes. However,
sometimes the behaviour of the applied system may
not be as expected, because of inadequate knowledge
and the complex nature of the costal processes. Even
recently executed coastal projects have shown
undesirable effects on the coastline.
Materials and Methods
Dredging for port development generally lead to
significant changes in the configuration of the seabed.
These changes can significantly modify the currents,
waves and water quality in the project area. These
effects include1:
• Changes in circulation patterns and sediment
transport processes;
• Low mixing and poor water quality near the
bottom of dredged basins and channels, resulting
in low levels of dissolved oxygen;
• Potential for increased salinity intrusion in
estuaries;
• Potential for local increase in wave heights due
to changes in wave refraction patterns;
• Potential for increased sedimentation rates and
future maintenance dredging requirements and
• Potential for beach erosion due to loss of sand
sources.
Breakwaters and other large-scale port structures
can greatly affect local wave conditions, currents and
sediment transport processes and can cause significant
changes in the configuration of the adjacent shoreline.
Particularly severe effects can occur at open coastal
sites with high energy conditions and high rate of net
longshore sand transport. In such cases the breakwater
will block the longshore transport, causing rapid
deposition on the updrift side and concurrent erosion
of the coastline on the downdrift side. Coastal erosion
problem can be mitigated by periodic beach
nourishment by dredging sand from offshore sources,
bypassing the impounded sand on the updrift side of
the port or providing sand from upland sources. Coastal
structures such as groynes can be used in combination
with beach nourishment to reduce long-term
maintenance costs.
The impact of port development on the coastline
(especially due to obstruction to the longshore drift)
in the Indian scenario has been discussed in this
paper. The mitigation measures adopted by some of
the ports with their advantages and limitations are
also discussed, which would provide guidelines for
the future developments.
598
INDIAN J MAR.SCI., VOL 39, NO. 4, DECEMBER 2010
Results and Discussion
Coastal Processes
Construction of breakwaters, jetties, and other
structures on the coast should ensure that the adjacent
coast and beaches are not affected. In general these
tasks are not compatible to each other. Commonly
construction of such structures has adverse effect on
the adjacent beaches and may even affect beaches
some distance away. The coastal engineer has to
foresee this and try to prevent such damage by
adopting appropriate shore protection measures. An
understanding of the processes involved in the
near-shore region is essential for this purpose.
The environmental forces acting on the beaches
and coasts give rise to a variety of coastal processes in
the nearshore region. Major environmental forces
which are important for coastal processes are waves,
tides, currents, wind and storm surges.
Coastal currents are responsible for large sediment
transport along the open coast. These currents are
influenced by tides and morphological features of the
region, and generally the sediments transported are of
fine nature. The wave action results in causing shear
on the sea bed due to oscillatory currents. In the close
vicinity of the coastline, the dominant effect is due to
breaking of waves. Wave interaction with the
coastline results in onshore, offshore and alongshore
movements of sediments. The littoral drift prevalent
due to wave action is a function of wave and beach
properties and shows seasonal variations. During the
variation of the water level with the tides, the zone of
sediment transport due to waves also changes.
Particularly in the regions, where the tidal ranges are
more than a half meter, the water level variation
considerably influences the beach behaviour. At the
coastal inlet, the sediment transport process is
complicated by influence of the tidal currents.
Typically during the flood tide, the sediment transport
takes place from the shallow bar region to the inside
of the inlet which settles on the inside shoals and
during the ebb tide, part of it, is transported back to
the sea with the flow. The shallow bar at the entrance
provides a bridge for transporting the sand from
updrift to downdrift directions depending on the
prevalent wave directions. In the case of wide
estuaries, the sediment transport takes place in
different reaches, and shows considerable spatial
variations. The density currents due to salinity mixing
process also influence sediment transport having
upstream oriented bias. In the case of gulf, generally
the tidal ranges are large and are associated with the
strong tidal currents. The wave action on the gulf
banks are spread over a wide region. The magnitude
of sediment transport is also large in these regions.
Effects of Construction of Coastal Structures
Construction of major, intermediate and minor
ports on open coast causes considerable changes in
the vicinity in majority of the cases. These effects
include accumulation of sediment on the updrift side
with progressive advancement of the shoreline and
erosion of the coastline on the downdrift region. Since
major port developments involve construction of the
breakwaters much beyond 4 to 5 m depths, major part
of the littoral drift is blocked on the updrift side and
corresponding inevitable lack of sediment supply on
downdrift side. Due to prevalence of large wave
energy on downdrift side the coastline gets eroded
severely with formation of even large embayment.
The effect can extend to even 8 to 10 times the length
of the protrusion. Dredging of a channel for
navigation at the entrance of the port also disrupts the
sediment supply on the downdrift side. When there is
strong directional bias in the littoral drift process, like
on the east coast of India, the effects of accretion on
the updrift side and the erosion on downdrift side
have been aggravated over the years with only
marginal reversing trends. The accumulation on the
updrift side also has adverse effects like choking of
inlets, progressive advancements of the shoreline
which in effect reduce the tidal exchange with the
backwaters and adversely affect water quality in the
lagoons/rivers/creeks. Even though, there is overall
eroding trend on the downdrift side, there could be
formation of small fillet on the downdrift side due to
influence of the diffracted wave flux from the
breakwater tips and marginal reversal of littoral drift
in the other season.
The adverse effects of the undesirable erosion and
accretion can start even at the construction stages of
the port development. These adverse effects can be
excessive erosion as well as undesirable shifting of
the sand in the port development area. The large scale
bathymetric changes may lead to modifications in the
originally planned structures. In the event of
providing seawalls in the eroding reaches, adverse
effect could be the excessive deepening in front of the
seawall and erosion on the downdrift side. With the
deepening in front of the seawall, larger and larger
waves approach the seawall causing damage.
In the case of construction of short breakwaters in
the vicinity of coastal inlets, the effects on the
KUDALE at el IMPACT OF PORT DEVELOPMENT ON COASTLINE
shorelines are prominent. There is an accumulation on
the updrift side and corresponding erosion on the
downdrift side immediately due to construction of
such training bunds/breakwaters. The deepening of
the river inlet, which is suitable for navigation, also
results in transport of sand to deeper reaches. With the
deployment of short length bund, not only
accumulation occurs on the updrift side but also
accumulation tends to block the inlet.
Many a times, more than one project is executed in
close proximity and the combined effect of all such
developments with the proper time frames are
required to be visualized to identify the likely erosion
and accretion trends. In the case of deltaic regions of
large rivers, the effects of tidal currents and the fresh
water discharge are prominent and beyond the control
by containing the local hydraulic parameters.
Moreover, such deltaic regions are part of the large
scale morphological processes and these large scale
changes many times cause severe erosion or accretion
trends of undesirable nature.
Pre-Assessment of the Projects
For site specific investigations, the processes to be
examined are wave climate in different seasons, tidal
flow patterns with seasonal effects, effect of fresh
water discharges, sediment transport and beach
behaviour. Estimation of littoral drift and sediment
budgeting are the most important for prediction of
likely morphological effects.
Variety of coastal protective measures has been
tried in mitigating erosion caused naturally as well as
due to human interference. These coastal protective
measures have their own advantages and
disadvantages. The following aspects need to be
considered while suggesting the appropriate solution
for the coastal erosion:
(i) Seawall with steep impermeable slope tends to
cause reflection of the waves resulting in the
depletion of the beach on the foreshore. Severe
wave attack on the seawall progressively.
(ii) Groyne field also requires adequate supply of
sand for their effectiveness and can cause
erosion on the downdrift side if all the supply
of sand is trapped.
(iii) Detached offshore breakwater tends to provide
beach in the shadow zone, for which adequate
supply of sand for beach formation is required.
(iv) Artificial beach nourishment revives the beach
but for its success periodic nourishment and
containment of sand by providing small
groynes are required. Sand bypassing
utilization of the dredged material from
ports for the beach nourishment on
downdrift side, is an excellent method
coastal protection.
599
and
the
the
for
Case Studies
The case studies discussed in the following
paragraphs can provide some vital guidelines for
introspection and for the planning of future port
development projects.
Chennai and Ennore Reaches, Tamilnadu
The coastline behaviour in the Chennai-Ennore
reach has revealed many important aspects. For
example, the effects like formation of an extensive
beach on the south side (Marina beach) and
progressive erosion and eventually formation of
Royapuram Bay has been well documented in the
coastal engineering literature5 more than 50 years
back. The formation of a beach on the south side has
been used with advantage for various urban
developments and the region has been the pride of
Chennai City. Even the formation of the Royapuram
Bay, which had been of concern, has been eventually
used for extension of major port and for the
development of fisheries harbour with minimal capital
dredging. However, it is well known that severe
erosion has resulted in the northern reaches up to
Ennore, which has aggravated over the years despite
some local protection works.
The Marina beach had beneficial effects of
providing vast additional land area for urban use.
However it is adversely affecting the hydraulic
exchange mechanisms in the Cooum River, which has
been a sore feature in the region. Progressive seaward
advancement of the Marina beach has aggravated the
Cooum river problem. In the year 2000-2001,
construction of groyne/training jetty of 150 m length
on the south side of the Cooum river has not only
aggravated the choking of the river inlet but also has
caused erosion in some reaches of the Marina beach.
The Ennore port, situated about 13 km north of the
Chennai Port is located between two coastal inlets viz.
Ennore inlet and the Pulikath inlet. The port
development has caused large scale changes in the
surrounding regions. These changes started during the
construction stages of the port affecting the area
within the port as well as on south and north sides of
the port. Excessive accumulation of the sand on the
south side has resulted in increase of the beach width
600
INDIAN J MAR.SCI., VOL 39, NO. 4, DECEMBER 2010
in front of the Ennore inlet. The sand barrier between
Pulikath Lake and the sea on the northern side of the
port has suffered severe erosion. Series of groynes
have been provided recently to mitigate erosion of the
reaches between Ennore port and Chennai fisheries
harbour. Small deposition of sand is also seen
between the groynes. However, there is no adequate
supply of sand from the south side for the expected
beach development between the groynes.
The coastline from the region south of Cooum river
upto the north of the Pulikath Lake reveals that the
coastal erosion involves very extensive areas. The
remedial measures like groyne fields adopted in the
reach between the Ennore port and the Chennai
fisheries harbour are required to be nourished. The
proposed developments of the Chennai port like
creation of the reclamation on seaward side of the
breakwaters or extension of the port, development of
sand trap and Cooum river improvement are also
required to be studied in totality rather than in
piecemeal. The sand from the capital dredging
operation of Chennai and Ennore Port have seldom
been made use of for mitigating the overall coastal
erosion problem. Presently, the sand is disposed off
at –20 m contour to avoid re-entry of the sand in the
approach area of the fisheries harbour of Chennai
Port. Beach nourishment by using the sand
accumulated in the sand trap of the Chennai Port can
ease the erosion north of the fisheries harbour.
Visakhapatnam Port, Andhra Pradesh
The shoreline near Visakhapatnam Port has been
marked by the presence of a rocky headland with
narrow beaches (Fig. 1). Even when only the inner
harbour of Visakhapatnam was developed, the beach
behaviour had been very carefully monitored.
Creation of navigation channel for the inner harbour
by intercepting sand in the sand trap, protection
against waves by using sunken ships and sand
bypassing with the use of dredgers and floating
pipeline had been in vogue even before 1960s when
the outer harbour development was taken up. Since
the length of the breakwaters of the outer harbour had
been more than 1500 m, most of the littoral drift was
blocked. Studies for morphological aspects like
littoral drift, provision of sand trap and sand bypassing
were taken up prior to the project and helped in
identifying the exact need of bypassing/beach
nourishment on the northern beach2. Sand trap has
been provided in a gap between the western tip of the
south breakwater and Dolphin Nose Headland
(Fig. 2). Presently, the dredger bypasses the sand from
a jetty by using shore connected pipeline, which has
been proved a successful strategy.
The beach nourishment has been optimized by
extensive studies at CWPRS2. The need for bypassing
at least 0.3 million cum of sand yearly, on the
northern beach has been identified. Considering the
existence of a fisheries harbour facing north and a
Catamaran basin and the need to avoid formation of
shoals in their approaches, the beach nourishment is
presently required to be restricted but with more and
more bypassing, wider sandy beach can be ensured3.
Case of Visakhapatnam Port shows how prior studies,
judicious and careful planning of dredging operations
and continuous monitoring can help in stabilizing
Fig. 1- Imagery of Visakhapatnam Port and Adjacent Coast.
KUDALE at el IMPACT OF PORT DEVELOPMENT ON COASTLINE
adjacent coastline in effectively despite the large
littoral drift in the region.
Paradip Port, Orissa
Port of Paradip is another case where triggering of
coastal erosion due to obstruction to the littoral drift is
clearly evident (Fig. 3). The construction of two
601
breakwaters caused accretion on the southern side and
erosion on the northern side. The port had installed a
sand pump on a trestle constructed south of the south
breakwater, so that the material accumulating on the
southern side could be pumped across to the eroding
northern beach. However, there were problems in
operating the pumps and the trestle was damaged
Fig. 2- Layout of Visakhapatnam Port Showing Breakwaters and Sand Trap.
Fig. 3- Imagery of Paradip Port and Adjacent Coast.
602
INDIAN J MAR.SCI., VOL 39, NO. 4, DECEMBER 2010
during a cyclone in 1972. This resulted in short supply
of sand to the northern beach, causing erosion. A
seawall of about 5 km length was constructed from the
root of the northern breakwater along the coast to
prevent erosion of the shoreline. Though the seawall
has been found to be successful to a certain extent in
preventing the landward encroachment of the sea,
reflection of waves caused scouring at the toe of the
seawall. The effect of erosion can be seen in
deepening/scouring of the coast which has resulted in
shoreward shifting of the -3 m and -5 m depth contours
(Fig. 4). Nourishment of the northern beach by sand
bypassing would be the best solution for the problem.
Coastline near Mangalore, Karnataka
The coastline near Mangalore has witnessed many
developments over the last four decades. The major
development had been the construction of the new
Mangalore port which is an artificially developed
lagoon type harbour with depths of about –15 m in the
channel and the port basin. Two breakwaters have
been provided on the south and north sides of the
channel. As a result of all these developments, there is
limited movement of sand across the harbour.
Generally, there is tendency of the sand movement
from the north to south due to northwesterly waves
during the non-monsoon season and westerly waves
during the southwest monsoon. Some littoral drift
occurs from south to north direction at the beginning
of the southwest monsoon season. The shoreline and
the overall foreshore on the north side show almost a
stabilized trend4.
Subsequently a minor port (Old Mangalore Port)
had been developed at the inlet where Gurpur and
Netravati rivers meet the Arabian Sea, about 10 km
south of the New Mangalore Port. Two training walls
(breakwaters) were constructed to provide protection
against waves to the vessels entering the port through
the approach channel (Fig. 5). The breakwaters also
Fig. 4- Increase in the Depths on Northern Coast of Paradip Port.
Fig. 5- Imagery Old Mangalore Port at Ullal Inlet.
KUDALE at el IMPACT OF PORT DEVELOPMENT ON COASTLINE
channelise the river discharge/tidal flow and help in
stabilizing the inlet. The depths over the sand bar in
front of the mouth are also maintained by the
channelized flow. The construction of 375 m long
north breakwater (Bengre Point) and 580 m long
south breakwater (Ullal point) was completed in
1994. After the construction of breakwaters, the
northern beach (coast between North breakwater of
Old Mangalore Port and south breakwater New
Mangalore Port) started accreting and within a couple
of years, deposition of sand reached beyond the
roundhead of the north breakwater. Seasonal changes
in the south beach (Ullal) were seen, however, there
was net erosion, which caused recession of the
southern coastline (Fig. 5). The beach width along the
southern coastline at Ullal has been reduced
considerably and the foreshore depths have been
increased. A sand bar is also formed between the tips
of breakwaters. Offshore submerged reefs along with
the beach nourishment would appropriate solution for
preventing erosion at Ullal.
Inlet at Beypore, Kerala
Under natural conditions, the Inlet of Beypore
River had a wide half moon shaped sand bar with
depths of not more than 1.2 m. The inlet also showed
considerable cross-sectional variations. These
conditions have been unfavourable for navigation of
fisheries crafts. The improvement scheme comprising
about 800 m long parallel breakwaters have enabled
providing depths of about 4 m and removal of shallow
bar. There has been an advancement of the shoreline
on the north side but after its stabilization, the depths
at the tip of the northern breakwater have remained
more than 3 m. This can be particularly due to small
littoral drift in the region and some natural bypassing
across the inlet. The shoreline on the south side;
however, is showing accretion mainly because of the
river borne sediments, which are flushed out of the
inlet during monsoon season.
Inlets at Bhawanapadu and Nizamapatnam, Andhra Pradesh
The coastal inlets of Bhawanapadu and
Nizamapatnam on Andhra Pradesh show prominent
influence on the littoral drift. In the case of
Bhawanapadu inlet, prior to training of the inlet,
natural bypassing was taking place on the shallow bar
at the river inlet. After construction of two long
training walls/breakwaters for fisheries development,
significant changes occurred in the region. Excessive
accumulation of the sand on the south side has
resulted in advancement of the shoreline and
603
formation of a wide bar in front of the breakwater
entrance in a short time. The shoreline on north side
has shown considerable erosion. Under the present
conditions the inlet has been very shallow and the
shallow bar on the seaward side of the breakwater
entrance has almost choked the entrance. Even
though the northern coastal erosion has not been
considered a problem, improvement of the inlet
by dredging is needed for navigation. The sand
getting deposited in the channel can be periodically
bypassed to the north.
In the case of Nizamapatnam, the littoral drift has
not been as large as compared to Bhawanapadu inlet,
due to its different orientation. As a result,
advancement of the shoreline has occurred on both
the sides of the inlet after construction of two training
jetties/breakwaters at the entrance.
Development in Mirya Bay, Ratnagiri, Maharashtra
The Mirya Bay in Ratnagiri has excellent
conditions for port development due to stable bed
conditions in the main Bay with depths of more than
8 m. No major siltation occurred after the construction
of breakwater at the southern tip of the Bay for the
development of Bhagwati Bandar. A fisheries
harbour with two breakwaters was developed in the
southeast region of the Bay on a sandy beach. As a
result, excessive accumulation of sand has occurred
on north of the north breakwater and the approaches
to the fisheries harbour are getting silted up (Fig. 6).
On the other hand, severe erosion has occurred in the
northern portion of the Bay, for which seawall has
been provided. In order to contain the siltation
occurring in the fisheries harbour and to arrest
southerly movement along the Bay, T-shaped
groynes were suggested. These are yet to be
implemented. Recently a proposal of ‘providing
offshore reef in front of the northern coast and
artificial nourishment of the northern coast by
utilizing the sand deposits on the south side’ is under
active consideration.
Conclusion
The construction of breakwaters and dredging of
navigation channels for port development interfere
with the longshore littoral drift. The main impact
of the port development is accumulation on the
updrift side of the longshore drift and erosion of the
downdrift side. The impact is prominent on the
coastline having high rate of longshore sediment
transport.
604
INDIAN J MAR.SCI., VOL 39, NO. 4, DECEMBER 2010
Fig. 6- Imagery of Mirya Bay, Ratnagiri.
Sand bypassing (i.e. dredging of sand from the
updrift side and artificial nourishment of the
downdrift side) appears to be the best solution to
mitigate the problem of siltation and erosion.
Sand bypassing need to be made mandatory for
the port development projects and it should form
an integral part of the project at the planning stage
itself.
Sand removed during the capital and maintenance
dredging operations can form a very good source of
sand for beach nourishment to mitigate the adverse
effects likely to be caused by the project.
Different case studies reveal large differences in the
coastal setups and also reveal the major influence of
port development on the coastal regions. As such, it is
necessary to understand the coastal processes and
predict the likely effects before undertaking any
coastal project.
.Acknowledgement
The author is grateful to the Director, Central Water
and Power Research Station, Pune for his kind
consent for presenting this paper.
References
1
2
3
4
5
Gregory P Tsinker, Port Engineering, (John Wiley & Sons
Inc., USA) 2004, pp. 829-830.
Phani Kumar M, Joshi V B & Purandare U V, Sand Trap –
Salient Feature of Port on Drift-prone Coast, (National
Conference on Hydraulics-Hydro) 2001, pp. 358-364.
Phani Kumar M, Joshi V B & Purandare U V, Planning of
Coastal Structures for Development of Landing Facility for
Catamarans at Visakhapatnam Port, (National Conference
on Hydraulics-Hydro) 2003, pp. 234-239.
Jagadeesh H B, Joshi V B & Purandare U V, Long-Term
Effects on Siltation Patterns due to Developments at New
Mangalore Port, (National Conference on Hydraulics-Hydro)
2003, pp. 228-233.
Per Brunn, Port Engineering, (Gulf Publishing Co.) 1976,
pp. 493-563.