ARTICLE in JOURNAL OF COASTAL CONSERVATION · MAY 2015 Impact Factor: 1.10 · DOI: 10.1007/s11852-015-0389-5 ·
Coastal Protection Measures: Review paper Ali Masria(1), Abdelazim Negm(2) 1
Egypt–Japan University of Science and Technology (E–Just), Energy Resources and Environmental Engineering Department, P.O. Box 179, New Borg El Arab City 21934, Alexandria, Egypt, Email:
[email protected] 1
Egyptian Ministry of Higher Education (MoHE).
2
Chair of Environmental Engineering Dept., and Prof. of Hydraulics, School of Energy, Environmental and Chemical and Petrochemical Engineering, Egypt-Japan University of Science and Technology, E-JUST, P.O. Box 179, New Borg El Arab City 21934, Alexandria, Egypt, Email:
[email protected].
Moheb M. Iskander(3), Oliver C. Saavedra(4) 2
Associate Professor, Head of Hydrodynamic Department, Coastal Research Institute, Alexandria, Egypt.
4
Dr. of Eng., Associate Professor, Dept. of Civil Engineering, Tokyo Institute of Technology (2-12-1 Oookayama, Meguro, Tokyo 152-0033, Japan), Also Adjunct Faculty at E-JUST
Abstract – The rapid erosion in most coastlines is considered a major problem not only in Egypt, but also around the world. The main causes are due to anthropogenic activities and/or coastal hydrodynamics. The coastal zone suffer from sedimentation , accretion, and pollution problems as well as the side effect of climate change. The climate change will increase sea level rise , salt water intrusions, and storm surge. Major efforts has been exerted to manage coastal erosion problems and to restore coastal capacity in order to protect housing, infrastructure and the cultivated land. These problems was encountered with various types of hard structures but most of these methods response were limited due to lack in evaluation for the entire ecological situation. This encouraged the coastal engineers to think about new types of environmental friendly structures work better with ecological situation. In this study, the protection measures worldwide are reviewed and divided mainly into four groups, hard , soft, combined, innovative measures. The usage and side effect of each type is mentioned briefly. It is clear that there is a predominant approach towards the soft engineering , the eco-engineering techniques or combination between them in order to enhance ecological situation. Recently, there are several efforts to apply these new technologies to protect the coastal zone as well as the environment with taking into consideration the effect of climate change. These new approaches in coastal protection are multi used, environmentally friendly, easy to modify and maintain, and efficient from economic perspective. Previous efforts in solving coastal problems in Egypt are analyzed and discussed taking into consideration the experience from similar cases worldwide. It is clear that the environmental friendly coastal structure is more suitable to solve most of our coastal problems with saving our ecosystem and reduce the protection cost. Keywords: coastal erosion, hard, soft, protection, Egypt, innovative.
1.
Introduction
Coastal erosion is a global problem[1]. Erosion is mainly caused by natural processes and to a little extent by anthropogenic activities over a long period of time. The continuous decline in the size of the zone might also be influenced by steady rise in sea levels accompanied by subsistence of the lower delta plain[2]. The problem will be amplified if the sea level rises accomplish with the
occurrence of greater and more frequent storms, as coastal flooding and erosion problems will become exacerbated in vulnerable coastal areas [3]. At least 70% of the sandy beaches around the world are retreated [4]. About 86% of the United States east coast barrier beaches have experienced erosion during the past 100 years [5]. Widespread erosion is also well documented in California [6] and the Gulf of Mexico [7]. Previously, protection works were focused only on solving the local problem which causes in many cases the
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transformation of the problems to the adjacent coastal area. Coastal protection structures such as seawalls and rock revetments have been used for centuries to protect and prevent further loss of coastal lands that are bases of economic activities. Whilst successful in preventing shoreline retreat, preserving the dynamic coastal landscape, but their presence often contributes to the denigration of natural coastal habitats. These concerns were the impetus for research into alternatives to hard protection [8]. With the beginning of the last century, the environment impact assessment revealed and new concepts as the environment protection and sustainable development have been established. With this new approach, the concept of coastal protection is changed from hindering the natural forces to building with nature, [9]. This new approach, which is building with nature, requires the knowledge of the exact behavior of the coastal zone, and hence addresses the main reasons for the problem in order to choose its suitable protective structure. This should be followed by the environmental impact study to identify the side effects of this structure and its mitigation measures. Accordingly, over the last two decades, as the importance of preserving natural coastal resources were realized on a global scale, efforts have been made to migrate from the conventional approach of hard engineering to soft engineering and eco-engineering especially in environmentally sensitive areas[10]. The novelty of these solutions is their ability to sustain natural resources and even add-value to the coastline. In addition, new approaches to deal with the coastal problems appear. Three basic choices are possible: no action, re-planning the coastal zones and relocating the existing structures to be far from the sea, and executing positive corrective measures. Egypt constructed the first economic harbor worldwide west of Pharos Island, Alexandria about 1800 B.C., [11]. Egypt as one of the pioneers in coastal protection should start work with these new concepts to protect its coastal environment and increase its economic values. This environmental approach requires the cooperation of all the social communities, executive sectors, and educational institutions. This contribution presents an overview of the various available methods for shore stabilization and beach erosion control, highlight on the new approach in coastal protection in order to recommend a proper solution for the Egyptian coastal problems.
2.
Coastal protection measures around world
Protection of the coast and the shore against the forces of waves, currents, storm surge and flood can be performed in many ways. There are two kinds of protective measures for controlling coastal erosion: structural measures and non-
structural measures [1]. Structures can be divided into hard and soft structures. Nonstructural measures include land-use controls, setting warning lines such as the coastal setback line and coastal construction control line to protect the coast from improper construction, and prohibition of unreasonable sand mining and reclamation.
3.
Types of Coastal protection measures and Their Usage
The coastal protection structures can be classified into four classes: hard structures, soft structures, combination between both, and new innovation one. Hereafter is a brief note about each class and its subdivisions.
3.1.
Hard defenses
Hard-engineered structures are designed to reduce or prevent shoreline erosion and retreat [12]. They succeed at local scales [13]. However, hard-engineered structures hinder the propagation of the sand to the coast [14]. Additional problems exist in the fact that hard structures can impede the recreational use of beaches and can be costly to construct and maintain [11]. These costs and benefits need to be considered .There are many types of hard structures like; Seawalls Sea wall is constructed parallel to the coastline to act as a barrier ranging from concrete to sand bags, and can vary in term of design[15],The major benefit of sea walls is that it can provide a great defense against flooding and erosion while also immobilizing the sand of the adjacent beach, fig (1). Unfortunately, these structures are expensive and their effectiveness depends on shape and size. A sloped wall requires more space on which to build. Reflection of a wave off of a vertically built sea wall causes turbulence and therefore erodes the sand at the base of the structure. This erosion can weaken the sea wall itself and result in large maintenance costs [15]. Revetments A revetment is, just as a seawall, a shore parallel structure fig. (1). The main difference is that it is more sloping than a seawall. A revetment has a distinct slope (e.g. 1:2 or 1:4), while a seawall is often almost vertical, the surface of a revetment might be either smooth or rough (a seawall is mostly smooth) and that the height of a revetment does not necessarily fill the total height difference between beach and mainland (a seawall often covers the total height difference). Although revetments provide hard face to cliff, easily installed, cheaper than sea wall, deflects and absorbs wave power, but it needs frequent maintenance.
Bulkhead
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Bulkheads are normally constructed in the form of a vertical wall built in concrete, stone, steel or timber. The concrete, steel or timber walls can be piled and anchored walls, whereas the concrete and stone walls can also be constructed as gravity walls fig. (2). The function of a bulkhead is to retain or prevent the sliding of land at the transition between the land, filled or natural, and the sea. Bulkheads are only suitable for low energy protected sites where large waves are not anticipated Dikes and Levees Sea dikes are onshore structures with the principal function of protecting low-lying areas against flooding. Sea dikes are usually built as a mound of fine materials like sand and clay with a gentle seaward slope in order to reduce the wave run-up and the erodible effect of the waves. The surface of the dike is armored with grass, asphalt, stones, or concrete slabs., fig. (2). The advantages is that they often form the cheapest hard defense when the value of coastal land is low, and reduce wave loadings on the structure compared to vertical structures . The disadvantages is the requiring of large volumes of building materials and wide area in order to resist high water pressures on their seaward faces. Groins Groins are straight structures perpendicular to the shoreline, fig(3). They work by blocking (part of) the littoral drift, whereby they trap or maintain sand on their upstream side. Groins can have special shapes; they can be emerged, sloping or submerged, and they can be single or in groups, the so-called groin fields. Types of groins are wooden groins, sheet-pile groins, concrete groins and rubble-mound groins made of concrete blocks or stones, as well as sand-filled bag groins. The advantages are; building up the beach, makes a wider beach, provides calm water, and encourages tourism. The disadvantages are; need repairs, suitable with medium waves but strong waves still get to cliff face, and leads to faster cliff erosion down the coast by robbing it of potential beach material.
Breakwaters There are two types of breakwaters; the first one is detached breakwaters which are straight shore-parallel structures, fig.(3), normally built as rubble-mound structures with fairly low crest levels that allow significant overtopping during storms at high water. The low-crested structures are less visible and help promote a more even distribution of littoral material along the coastline. Submerged detached breakwaters are used in some cases because they do not spoil the view, but they do represent a serious nonvisible hazard to boats and swimmers . This decrease of transport results in trapping of sand in the lee zone and some distance upstream.. The second type is the breakwater that is connected to the coast, i.e. it is extending from the coastline to the offshore direction. This type of structures is used to protect harbors and navigation channels from wave action to create a calm area for ships and may be for swimming. Jetties A jetty is any of a variety of structures used in river, dock, and maritime works that are generally carried out in pairs from river banks, or in continuation of river channels at their outlets into deep water, fig. (4). Jetties are used for stabilization of navigation channels at river mouths and tidal inlets, and are in most cases designed as rubble-mound structures (breakwaters and groins) except that the outer part must be armored on both sides.
Figure 3: Two-row pile groins and adjacent shoreline position, Hel Peninsula (the Baltic Sea), (left)[20]. Detached breakwaters at Happisburgh, Norfolk, UK (right)[21].
Figure 4: Kaumalapau Harbor Breakwater, Island of Lanai, Hawaii (left). A jetty (right)[22]. Figure 1: Sea wall at Saint Jean de Luz ,(left)[16]. Major rock armour revetment in front of dune system, (right)[17].
Figure 2: Bayley Bulkhead, Scarborough, ME (left)[18]. A levee keeps high water on the Mississippi River from flooding Gretna, Louisiana, (right)[19].
3.2.
Soft defenses
Increasing awareness of the negative side-effects of hard structures on erosion and sedimentation patterns has led to growing recognition of the benefits of „soft‟ protection and the adaptation strategies of retreat and accommodate [23]. Beach Fills Beach nourishment requires the addition of sand to an eroded beach. Sand is imported and spread to increase beach width and elevation [24]. It is used worldwide as a
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form of soft engineering to protect coastal development from the impacts of unmanaged erosion [25]. It serves to maintain the value of coastal investments [26]and retain the value of beach amenity to tourism and recreation [27]; [28], figure (5-I). It allows the sand to shift continuously in response to changing waves and water levels. The advantages are: reducing the detrimental impacts of coastal erosion by providing additional sediment which satisfies erosional forces , beach nourishment is a flexible coastal management solution, in that it is reversible, and as a result of sediment redistribution by longshore drift, beach nourishment is likely to positively impact adjacent areas which were not directly nourished. The disadvantages; nourishment is not a permanent solution to shoreline erosion, periodic re-nourishments, will be needed to maintain a scheme‟s effectiveness. Sediment deposition can generate a number of negative environmental effects, including direct burial of animals and organisms residing on the beach. Dredging or Sand Bypassing Sand bypassing is the hydraulic or mechanical movement of sand, from an area of accretion to a downdrift area of erosion, across a barrier to natural sand transport such as large scale harbor or jetty structures. The hydraulic movement may include natural movement as well as movement caused by man. Bypassing commonly takes place by two main methods. First, pumping equipment and piping can be constructed that transfers sand from the updrift side of the littoral barrier, and deposits it as a slurry of sand and water on the downdrift side, figure (5-II). The second method involves the dredging or excavation of sand from the updrift side, using dredges or heavy machinery, figure (5-III), and the placement of this material on the downdrift side by the dredge (water based transport), or by trucks and other heavy equipment (land based transport). The advantages are: adding to tourist amenity by making bigger beach, attractive, and work with the natural processes of the coast. The disadvantages; needs frequent renewal of more sand, and does not protect cliff face from winter storm waves. Sand dunes stabilization Sand dunes are naturally wind-formed sand deposits representing a store of sediment in the zone just landward of normal high tides [29]. Dune/sand stabilization involves using structural controls and native vegetation to stabilize, build, or repair dunes. Vegetation can be used to encourage dune growth by trapping and stabilizing blown sand, figure (5-IV). Dunes provide habitat for highly specialized plants and animals, including rare and endangered species. They can protect beaches from erosion and recruit sand to eroded beaches. The side effects of these methods are nearly negligible and their costs are low compared with the hard structures. Sand dune stabilization commonly is used in conjunction with beach nourishment.
Sand dune stabilization face many of the same problems as does beach nourishment. Also, it hinders the development in the beach area , as the dunes require large amounts of land on which to build [15]. II
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Figure 5: Some types of soft defences from.
3.3.
Combined protection works:
• Submerged Breakwaters Submerged breakwaters can reduce beach erosion and protect coastal structures by dissipating a significant amount of wave energy [30]. They are coast-parallel, long or short; figure (6-I). Submerged breakwaters have small effect on the coastal environment and do not spoil the view. They have many types and shapes such as the wide crested breakwaters, narrow crested breakwaters and reef breakwaters. Recently there are many attempt to create a predictive empirical model exclusively for SBWs (submerged breakwaters) in terms of mode (erosion or accretion) and magnitude (size of salient) of formation by [31]. Perched Beaches Is the construction of a low retaining sill to trap sand and to elevate the beach above its original level. Perched beaches have many of the same qualities as natural beaches, and the submerged sill does not intrude on the view of the waterfront. Perched beaches are appropriate erosion control measures where a beach is desired and sand loss is too rapid for convenient or economical replacement. They can also be used to create a new beach for recreation and shore protection figure (6-II). Artificial Headlands Artificial headlands are rock structures built along the toe of eroding dunes to protect strategic points, allowing natural processes to continue along the remaining frontage, thus trapping littoral drift and creating a stable embayed beach. This is significantly cheaper than protecting a whole frontage and can provide temporary or long term protection to specific assets at risk. Temporary headlands can be formed of gabions or sand bags, but life expectancy will normally be between 1 and 5 years, figure (6-III).
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Figure 6: Some Types of combined protection from.
3.4.
Innovations in erosion control
More recent innovations have exploited advancements in specific areas of engineering associated with erosion control. Some of these techniques are as following:
4.4.1 Geotextile structures Geotextile systems utilize a high-strength synthetic fabric as a form for casting large units by filling with sand or mortar. Geotextile systems can be bags, mattresses, tubes, containers and inclined curtains. All of which can be filled with sand or mortar. Geotextile bags, or tubes are now gaining wide acceptance in coastal protection. They have been used as nearshore breakwaters (placed parallel to shore), as groins (placed perpendicular to shore) and even as revetments. Nearshore, low geotextile breakwaters are designed to a height sufficient enough to eliminate storm waves from reaching the shoreline but allows smaller waves to penetrate. Figure(7-I) show geotextile sandfilled breakwaters. Sand-filled bags are relatively flexible and can be repaired if some of the original bags are dislodged figure (7-II). In addition, stacked bags are suitable as temporary emergency protection measures. On the other hand, they are limited to low energy areas, have a relatively short service life compared to other revetments, and generally have an unattractive appearance. Installing structures of this type is rapid and less costly than heavy structures. They do not disturb the littoral ecosystem very much. I
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Figure 7: Geotextile types for coastal defences
4.4.2 Beach Drainage Systems (BDS) Beach drain concept initiated fifty years earlier . It worked in two parallel fields of coastal research: the role of beach face permeability in controlling erosion or accretion[32]and the tidal dynamics of beach groundwater [33]. The installation within the last ten years of prototype beach dewatering systems in Europe and the United States (Lenz, 1994) signified the transition of the beach dewatering concept from the hypothetical to the practical [34] . The Beach Drainage Systems (BDS) working principle is based on the concept that by keeping the groundwater level low, back-swash is inhibited by increased grain friction in a non-saturated medium. Percolation of 'swash water' into the beach means less backwash energy, which encourages suspended sand to settle out on the beach face. Saturated sand allows less sand to accrete than non saturated sand [35]. Increasing swash infiltration also slows longshore sand transport, which increase sand accretion locally [36]. Twenty four beach drainage systems have been installed since 1981 in Denmark, USA, UK, Japan, Spain, Sweden, France, Italy and Malaysia. There are two innovations based on improving the beach drainage have been tried and are discussed below: Beach Management System The Beach Management System (BMS) works on the principle that a saturated beach is more erodible than an unsaturated beach. This is achieved by draining water from buried, almost horizontal, filter pipes running parallel to the coastline. The pipes are connected to a collector sump and pumping station further inland. The buried shore-parallel drains of the BMS are in the form of perforated pipes wrapped in geotextile. Gravity drains the ground water beneath the beach and through the pipes to the sump and then the water is pumped from the sump. The sand filtered seawater can be returned to the sea or used for other purposes[37]. Figure 8 presents a schematization of the BMS.
Figure 8: Figure 8: Beach Management System - schematization,[37]
Pressure Equalization Modules This marine engineering system consists of polyvinyl chlorine (PVC) pipes strategically placed within the uprush zone to boost the vertical infiltration of seawater into the bed [8]. Several benefits from the implementation of this technology in coastal areas include the increase of erosion-resistance and the negligible alteration of biological and physicochemical beach characteristics [38],(see Figure 9). The infiltration of seawater into the bed is limited by the existing level of
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groundwater. Hence, if the groundwater can be lowered, more water from the run-up can percolate into the bed and less will run down the surface dragging sediments with the flow. In summary, the PEM increases vertical infiltration of uprush in the swash zone. The potential advantages of a beach drainage system include: 1. minimal environmental impact of the operating system compared with nourishment or existing hard engineering solutions, 2. provide a buffer zone from storm events and seasonal erosion and improved recovery time to pre-storm equilibrium following storm events, 3. protect of coastal fresh water environments from sea over-topping and seepage contamination, 4. better „natural character‟ outcomes than hard engineering or nourishment The disadvantages are represented in the following; limited to certain types of beaches. Also, sediment under the foreshore must be thick and permeable (between 0. 1 and 0. 5 mm) to allow pipelines to be installed and avoid clogging. Furthermore, a very slight slope is preferable from 1/10 to 1/50). Moreover, draining weakens one erosion process and does not solve the sedimentary deficit problem; thus it is better suited to bay head beaches (that make up a sedimentary compartment themselves).
Figure 9: Pressure qualisation Module-schematisation (left), and Pressure Equalisation Module pipe at Teluk Cempedak beach( right), (36).
4.4.3 Ecological engineering Ecological engineering integrates engineering principles with ecological and geomorphological processes [39] to create new ecosystems or restore systems that have experienced degradation or been destroyed [40]. For example, enhancing foredune vegetation increases sand accretion rates and dune elevation, which provide a greater buffer from advancing seas [41]. Ecological engineering can be used with the other adaptation options [42]. Preexisting hard engineered adaptation options can be retrofitted with design features, such as holes and caves that provide habitat [41]. For example, artificial habitat structures are attached to the seawalls in Sydney Harbor, Australia [43]. Increasing habitat and potential niches on hard-engineered structures at existing and/or new construction sites serves to facilitate decolonization of species displaced by hardengineered options [44].
Ecosystem engineering uses pioneer species to reengineer the environment or create habitat suitable to recruit other species forming an ecosystem [45]. For example, dune vegetation is commonly used in the rehabilitation of coastal dune systems as it stabilizes sandy beaches and captures windblown sand forming dunes [46]. Pioneer species can restart successional processes and prepare the new environment for subsequent colonizers. For example, dune plants reduce wind and wave erosion and protect less-tolerant plants from salt spray and storm damage [47].
4.4.4 Bio-technical Concepts The concept of bio-technical is based on producing coastal restoration products. Bio-technical structures are “soft” measures that both simulate natural coastal structures and enhance the growth of marine flora. For instance, “artificial seagrass systems”, when securely attached to the seafloor, play a crucial role in enhancing fish habitats [48]; [49]and reducing the velocity of the water current [50]. Similar to artificial sea grass habitats, “artificial mangrove roots” are another promising type of bio-technical structure. Based on the natural characteristics of the mangroves and their function as an efficient wave breaker, artificial structures provide protection to the shoreline developments in an event of storm surges, and also protect young mangrove seedlings from being washed away due to wave action [51]. Artificial Sea grass Many attempts at placing artificial seaweed mats in the near shore zone in an effort to decrease wave energy by the process of frictional drag were accessed ,figure(10). The most successful trials have been in areas of very low wave conditions, low tide range and relatively constant tidal current flows, when some sedimentation was found to take place. On open coast sites there have been major problems with the installation of the systems and the synthetic seaweed fronds have shown very little durability even under modest wave attack. The synthetic seaweed has tended to flatten under wave action, thereby having minimal impact upon waves approaching the coast. Field trials in the United Kingdom have been unsuccessful and the experiments were abandoned in all cases, due to the material being ripped away from the anchorage points. As it behaves as a drag barrier against often strong currents, much of the success of artificial grass systems are dependent on secure anchoring to the sea bed. Concrete block bases are frequently used as the anchoring mechanism [52].There are many experimental studies conducted to address the effect of sea grass on the wave dumping and velocities [53].
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Figure 10 : Natural sea grass (left) and artificial sea grass (right),[8].
Artificial reefs Artificial reefs reduce the wave energy liberated on the beaches behind them, it can be set on offshore or fore shore. They slow down the long-shore drift and favour foreshore growth, thus limiting erosion. They react in the same way as submerged breakwaters, and are often made up of coils or bags of geotextile, but other materials that can be used include sand, large blocks, concrete or pit run material. Low crested and submerged structures as detached breakwaters and artificial reefs are becoming very common coastal protection measures used alone or in combination with artificial sand nourishment, [54]. The main purpose is to reduce the hydraulic loading to a required level allowing for a dynamic equilibrium of the shoreline. To obtain this goal, they are designed to allow the transmission of a certain amount of wave energy over the structure in terms of overtopping and transmission through the porous structure (emerged breakwaters) or wave breaking and energy dissipation on shallow crest (submerged structures). Due to aesthetical requirements low, freeboards are usually preferred (freeboard around SWL or below). However, in tidal environment and frequent storm surges they become less effective when design as a narrow crested structures. That is also the reason that broadcrested submerged breakwaters (called also, artificial reefs) became popular, especially in Japan (Fig. 11). However, broad-crested structures are much more expensive and their use should be supported by a proper cost-benefit studies. On the other hand the development in alternative materials and systems, for example, the use of sand-filled geo-tubes as a core of such structures, can reduce effectively the cost ([55][56].
Figure 11: Example of Aqua reef, [57],( left), and Reef Balls units, [58], (right)
The relatively new innovative coastal approach is to use artificial reef structures called “Reef Balls” as submerged breakwaters, providing both wave attenuation for shoreline erosion abatement, and artificial reef structures for habitat enhancement. An example of this
technology using patented Reef Ball is shown in Fig. 11. Reef Balls are mound-shaped concrete artificial reef modules that mimic natural coral heads [58]. The modules have holes of many different sizes in them to provide habitat for many types of marine life. They are engineered to be simple to make and deploy and are unique in that they can be floated to their drop site behind any boat by utilizing an internal, inflatable bladder. Stability criteria for these units were determined based on analytical and experimental studies. Artificial Mangrove Root Systems Mangrove systems minimize the action of waves and thus prevent the coast from erosion. The reduction of waves increases with the density of vegetation and the depth of water. This has been demonstrated in Vietnam. It is proved the tall mangrove forests, the rate of wave reduction per 100 m is as large as 20% . Another work has proved that mangroves form „live seawalls‟, and are very cost effective as compared to the concrete seawall and other structures for the protection of coastal erosion [59]. Another function of this type is to trap sediment and thus acting as sinks for the suspended sediments . The mangrove trees catch sediments by their complex aerial root systems and thus function as land expanders. Experimentally, the influence of strength, shape and configuration (or arrangement) of an „engineered‟ mangrove root-system is currently being studied by local researchers to determine how they interact with waves [60]. Numerically, Zakaria and Febrina[61] studied the dispersion effects of wave propagation over mangrove models in shallow water environments. Figure 12 shows the natural and artificial mangrove.
: Figure 12: Natural mangrove roots (left) and an artificial mangrove roots system,south-east coast of India, (right),[62].
Though the limitations based on morphological, hydrodynamical and water quality conditions, to realize a combination between traditional engineering and ecological engineering is revealed, the inclusion of ecological engineering in coastal protection is shown to be a promising approach to integrate multiple functions in areas where demands for space are becoming more urgent every day [41]. Full-scale field projects are probably the only way to determine the effectiveness of eco-based techniques. However, when coastal projects are implemented, tried and tested methods are generally preferred over new innovations unless sufficient proof of success at pilot sites have been confirmed. Without major scale field experiments, bio-technical systems may be confined to be used as ancillary protection schemes.
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4.5 Potential Adaptation Responses In order to address the potential risks of climate change to existing assets and people, some form of protection is required for coastal environments, such as cities, ports, deltas and agriculture areas. Although the main focus is only on mitigation measures for climate, adaptation is necessary as climate changes and its effects are now inevitable [63],especially for coastal areas where there is a strong „commitment to sealevel rise and a commitment to adaptation‟ [64] Coastal protection to sea-level rise is often a costly, but a straightforward way to overcome the adverse impacts of climate change. Despite developing countries have very limited capacity to adapt, global and regional studies have highlighted that adaptation to climate change in developing countries is very vital and is an urgent priority. However, limitations both in human capacity and financial resources make adaptation difficult for the poorer nations such as Tanzania for example ([65]. The generic adaptation strategies are the following : 1. (Planned) Retreat – the impacts of sea-level rise are allowed to occur and human impacts are minimized by pulling back from the coast via appropriate development control, land use planning, and setback zones, etc. Managed retreat has been employed in a number of countries, including Australia and the United Kingdom, as an alternative to the construction and maintenance of hard- engineered structures [66]. However, to date, it has primarily been used in areas such as agricultural land, where the minimum economic impact is expected [67]. 2. Accommodation – the impacts of sea-level rise are allowed to occur and human impacts are reduced by adjusting human use of the coastal zone to the hazard through early warning and evacuation systems, increasing risk-based hazard insurance, increased flood resilience (e.g., raising houses on pilings), etc. 3. Protection – the impacts of sea-level rise are controlled by soft (e.g., beach nourishment) or hard (e.g., dikes construction) engineering, reducing human impacts in the coastal zone that would be impacted without protection. However, a residual risk always remains, and complete protection cannot be achieved even in the richest and more developed countries, such as The Netherlands. A list of the physical impacts of sea-level rise and some examples of potential adaptation responses illustrating these three generic strategies can be seen in[68]; [64] . The choice and use of these adaptation strategies with the objective of protecting the human use of the coastal zone would generally depend on the nature characteristics of the coastal zone and the type and extent of impacts [64]. For instance, unlike the first option (protection), the two adaptation strategies (accommodation and retreat) reduce or avoid the problem of „coastal squeeze‟ (preventing onshore migration of coastal ecosystems) between fixed coastal defences and rising sea levels. However, soft protection measures
(such as beach/shore nourishment and sediment recycling) can minimize this problem. It is also important to identify the benefits of applying adaptation strategies (see [69]), for example dikes can be combined with building codes/flood-wise buildings and flood warning and evacuation systems, and quite different adaptation strategies might be applied in a city versus a rural area. In regards to local shoreline management options, responsibility may fall either upon an individual property owner or on a community as a whole ([70]. In addition, ” there are three major constraints on what an individual can do in terms of coastal management. These constraints include: “…local and state rules and regulations including building standards that pertain to land use and development in shoreline areas [71].
4.6 Egypt coastal protection measures Nile Delta suffers a lot of coastal issues such: shore line retreat, pollution , salt water intrusion, etc. Also, an important parameter is the vulnerability to the impact of climate change and related sea level rise. Due to large subsidence in the Nile delta region, Egypt is considered one of the top five countries expected to be mostly impacted with a 1 m sea level rise resulting from global warming [72]. Egypt is ranked as the fifth in the world concerning the impact on the total urban areas, Egypt‟s GDP would be significantly impacted, and Egypt‟s natural resources such as coastal zone, water resources, water quality, agricultural land, livestock and fisheries maybe subjected to vulnerability. Moreover, Egypt may face environmental crises such as shore erosion, saltwater intrusion, and soil salinity. The adaptation measures that were identified to deal with the impact of climate change on coastal zone areas include: beach nourishment, construction of groins and breakwaters, tightening legal regulations, integrated coastal zone management and introducing changes in land use [73].
4.6.1. Traditional coastal measures (Hard) • Seawalls: The old Mohamed Ali seawall at Abu Quir bay, the old Burg El Burullus seawall, and the old seawall west of Damietta Nile estuary are some examples of the usage of this structure in the past to protect the Egyptian coast. Mohamed Ali seawall is the oldest seawall in the country which constructed to protect the low lying industrial district of Alexandria (some of it up to 3 m below sea level). However, extensive erosion is identified in front of this wall before its modifications to slope the face which improved the situation, [74]. • Revetments : This kind of structures is widely used in Egypt in the east and west of Rosetta estuary, the east side of Burg El Burullus, east of Damietta Nile estuary, and for the protection of the sea road west of Port-Said.
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These structures increase the erosion rate in front of them and shift the erosion problem to the downdrift areas, so they are used when no beaches in front of them are required. • Breakwaters: This type is widely used in Egypt at northwestern coast as in Marabella and 6th of October resort village, and Delta coast as in Baltim, Damietta, and El Gamil areas. The second type is the breakwater that is connected to the coast, i.e. it is extending from the coastline to the offshore direction. This type of structures is used to protect harbors and navigation channels from wave action to create a calm area for ships and may be for swimming. In Egypt this type is used in Sidi Kerair port, Sidi Kerair coastal resort, Edku LNG harbor. All of these structures cause sedimentation and erosion problems in the updrift and downdrift zones respectively, [75], [76] . • Groins: Some examples of using this structure along the Egyptian coast can be found in: the middle part of Marina El-Alamien center, El Mandara beach, east and west of Rosetta protection works, east Baltim sea resort, and on the western and eastern sides of El Arish port,. Typical shoreline changes are observed around these structures. • Jetties: They are widely used in Egypt on the both sides of the artificial lagoon inlets of El Alamien marina center, Maadia outlet, Burullus lake outlet, Damietta Nile estuary and El-Bardawil Lake outlets,. Sand accumulated on the western side of these jetties and noticeable erosion found in the eastern sides. It is clear that the tradition coastal structures, which used along the Egyptian coasts, have side effects on the environment and considered as overload on Egypt‟s economy. In general, applying hard defenses in Egypt proved to be unsuccessful as it conveys the problem from one side to another as it represent a constraint for the natural process.
4.6.2 Soft protection measures • Beach Fills: Six successful projects of sand nourishment were executed within Alexandria coast during the period from 1986 to 1995. Most of these beaches are still acting well. • Dredging or Sand Bypassing: Some dredging projects are executed within the Egyptian coast in Edku LNG harbor and its navigation channel, Rosetta estuary outlet, Damietta harbor navigation channel, and El Manzala lake outlets. The soft approach may be the most successful option with or without the hard one.
4.
Proposed Coastal Protection for the Egyptian coasts
It is difficult to obtain a proper technique for all kinds of coastal problems or preferred from an environmental standpoint[77]. We have consider the environmental side for each region, and address the suitable alternatives of
protection measures based on identifying coastal processes in order to obtain an idealized solution.
4.1.
Proposals
1. Apart from the protection already in place, Coastal Research Institute, Egypt has a list of proposals for more barriers to be built. The international highway could be elevated to 5 m above the sea level with „a wall on the side facing the sea‟; sand dunes should be protected and restored to function as natural walls; all development in the Delta ought to be subject to integrated management and planning to ensure that no new structures are put in the wrong place, [74]. Beaches should be nourished. A method already deployed with some success, beach nourishment entails a regular, recurrent deposition of sand onto beaches to uphold and strengthen their lines of defense against the sea. Large-scale transportation of sand could be organized on the basis of Egypt‟s practically unlimited desert reserves. 2. Proposals for solving problems in the Nile Delta coastal zone, [77]: First of all, there is an erosion problem due to the lack in sediment supply from the River Nile. This problem can be overcome by dividing the beaches into small cells by using headlands. The numerical and physical modeling can identify the suitable cell size .This solution may have the ability to minimize the sediment transport outside each cell and stop the retreat of the beaches. The flood problems of the low land and sabakha can be partially stabilized by using sand dunes with vegetation to support the outside face. Siltation problem of the lake entrances, drains and river outlets can be solved by dredging or by increasing the water velocity across the mouth by using the equilibrium cross section or by using open cycle pumping system. Constructed jetties with sand bypass from upstream side to downstream side can also solve this problem. The pollution problem in the northern lakes can be solved by controlling the pollution sources or by the increase of circulation system between the lakes and the sea. 3. A new technique to overcome Rosetta shoreline erosion is under development depending on reestablishment of natural hydrologic conditions such as providing a unique discharge processes and sediments through the estuary to enhance the stability of Rosetta estuary, Masria PhD study.
5.
Conclusion
This paper has investigated the different types of coastal protection defenses used around the world. In this investigation, the aim was to assess each type of coastal protection by identifying its advantages and
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disadvantages in order to suggest suitable protection method for the Egyptian coasts . The protection types are divided into four categories, hard, soft, combined, and innovative ones. One of the more significant findings to emerge from this study is that you can't stop the invasion of the sea by putting obstacles in front. It is shown from above cases that most traditional ways of protection which were used around the world , and our Egyptian coast have side effect on the environment and beach morphology. Also it has a relatively high construction and maintenance cost. The findings of this study suggest that , using the innovative techniques with the soft ones (beach nourishment, sand dune stabilization) can affect significantly on the restoration of the beach without affecting the environment , and the habitat of aquatic organism. The second major finding particularly in Egyptian coast is that, many coastal problems can be solved by reach the natural situation before the building of Aswan high dam. Because the stop of sediments and flow create a disrupted situation represented in severe erosion, water degradation. This situation can be achieved by artificial flood, sand engine and redistribute the end points of the drainage system. Further work needs to be done to identify whether the innovative techniques are suitable for Egyptian coast. Also, more experimental work needed to be done in order to address the all characteristics of these techniques. Also, the ICZM strategy is the predominant attitude of almost all the world to achieve the sustainable use of coastal zone resources, preserving biodiversity and habitat.
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ACKNOWLEDGMENT The first author would like to thank Egyptian Ministry of Higher Education (MoHE) and Egypt-Japan
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University of Science and Technology(E-JUST) for their support. AUTHORS’ INFORMATION 1,2,4
Department of Environmental Eng., Egypt-Japan University of Science and Technology, E-JUST . 3 Hydrodynamic Department, Coastal Research Institute, Alexandria, Egypt. The group is very interesting in the fields of hydrodynamics. The group is interesting in using SMS in simulating the coastal processes and sediment transport.
