Impact of port development on the coastline and the need for protection

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1 Indian Journal of Geo-Marine Sciences Vol. 39(4), December 2010, pp Impact of port development on the coastline and the need for protection M D Kudale Central Water and Power Research Station, Pune , India [ kudale_md@cwprs.gov.in] 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 include 1 : 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.

2 598 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

3 KUDALE at el IMPACT OF PORT DEVELOPMENT ON COASTLINE 599 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 and utilization of the dredged material from the ports for the beach nourishment on the downdrift side, is an excellent method for coastal protection. 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 literature 5 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 , 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

4 600 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 beach 2. 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 CWPRS 2. 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 ensured 3. 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.

5 KUDALE at el IMPACT OF PORT DEVELOPMENT ON COASTLINE 601 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 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.

6 602 INDIAN J MAR.SCI., VOL 39, NO. 4, DECEMBER 2010 during a cyclone in 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 trend 4. 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.

7 KUDALE at el IMPACT OF PORT DEVELOPMENT ON COASTLINE 603 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 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 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.

8 604 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 Gregory P Tsinker, Port Engineering, (John Wiley & Sons Inc., USA) 2004, pp 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 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 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 Per Brunn, Port Engineering, (Gulf Publishing Co.) 1976, pp