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Coastal Management Final

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    Katarina Chow (33) 3R

    Introduction

    The increasing attacks of the natural disasters and drastic change of the climate in

    the recent decade has resulted in massive amount of coastal and soil erosion along

    the coastal regions. While the rising economic concerns and stakeholder pressure

    on environmental sustainability of coastal and marine structural materials is in favour

    of a comprehensive and integrated approach. Current coastal management has

    focused on egocentric vision, recognizing the ecological uniqueness and particular

    value of the coastal zone. Coastal zones contain rich resources and are home to

    most commercial and industrial activities. In the European Union, almost half of the

    population now lives within 50 kilometres of the sea and coastal zone resources

    produce much of the economic wealth. Coastal protection takes consideration the

    balance of economic, ecological and social factors when measures are being

    implemented.

    In the past, the general practice was to use hard structures to protect the coastline.

    These structures include sea walls, revetments and groynes etc. (Please refer to

    next page for more details ). In certain resort areas, structures had proliferated to

    such an extent that the protection actually impeded the recreational use of the

    beaches. Erosion of the sand continued, but the fixed back-beach line remained,

    resulting in a loss of beach area.

    As new techniques were developed, the use of artificial beaches and stabilized

    dunes as an engineering approach was an economically viable and more

    environmentally friendly means for dissipating wave energy and protecting coastal

    developments.

    When the high flood tides and surges were absorbed by salt marshes along the

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    coast, these areas (e.g. in the Fens, Romney Marsh and Pett Level, Thames

    Esturary) were reclaimed to create fertile farmland over the years. From time to time

    these areas are flooded by the sea, and have been protected by higher and higher

    sea walls. As sea level rises owing of the Greenhouse effect it will cost increasing

    amounts to protect this land. In addition, changes on sea level have a direct

    adaptative response from beaches and coastal systems. When the sea level rises,

    coastal sediments are in part pushed up by wave and tide energy, so sea-level rise

    processes have a component of sediment transport landwards. This results in a

    dynamic model of rise effects with a continuous sediment displacement.

    Over the past hundred years the limited knowledge of coastal sediment transport

    processes at the local authority level has often resulted in inappropriate measures of

    coastal erosion mitigation. In many cases, measures may have solved coastal

    erosion locally but have exacerbated coastal erosion problems at other locations -up

    to tens of kilometers away- or have generated other environmental problems.

    In brief there are two types of coastal management- the hard engineering and soft

    engineering. We will discuss how each measure was in protecting the coastline in

    their respective places.

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    Seawalls

    Seawalls are built along the coast to protect valuable or resources. There are vertical

    Sea wall and Curved Sea wall. They absorb the energy of the waves before they

    can erode away loose materials. It can be made of concrete, rocks or wood. They

    can be found along the coasts of Penang , Malacca and Singapore. However, the

    energy of the waves would be redirected downwards to the base of the seawall that

    may cause a strong backwash. This backwash would further wear away the base of

    the seawall over years, causing it to weaken and eventually collapse if it is not

    carefully maintained. Seawall are costly to build and maintain as there constant

    repairs to be carried out throughout the years. As the strait of the seawall can be

    very long along the coastline, it can serve as a recreational purpose. Stanley Park

    Seawall in Vancouver is a good example.

    Stanley Park Seawall

    Vertical seawall

    Vertical seawalls are generally constructed in very exposed areas. They reflect

    waves. In severe storm situations, the walls can cause standing waves to develop.

    The seawall is the 22km pathway in Vancouver's waterfront from the convention

    centre on Burrard Inlet, around Stanley Park and False Creek, past Granville Island

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    and ending at Kitsilano Beach Park. It is the most popular recreational facility in

    Vancouver and is also a tourist attraction. The seawall is managed by the Vancouver

    Park Board together with City of Vancouver Engineering Services.

    The seawall is divided into two sections, one for walkers and joggers (closest to the

    water) and another for cyclists and inline skaters (inside path). Signs indicate use

    and warn of congested areas: Bikes must be walked in three areas in Stanley Park

    due to congestion.

    The seawall passes through 16 parks and past four community centres and nine

    concessions. Construction of this seawall began in Stanley Park in 1917 and not

    until 1980, the entire seawall loop around Stanley Park was declared officially

    completed with the final paving between Third Beach and Second Beach. Since 1980

    the seawall has been extended outside of Stanley Park.

    In 2010/2011, two portions of the seawall, Stanley Park (near Second Beach) and

    English Bay (near Sunset Beach) were renewed to address ongoing concerns with

    erosion. With deep foundations and renewed surfacing, the new seawall is built to

    withstand the tides for many years to come.

    Overall, the Vancouver Seawall is a prime example of how seawalls can

    simultaneously provide shoreline protection and a source of recreation which

    enhances human enjoyment of the coastal environment. It also illustrates that

    although shoreline erosion is a natural process, human activities, interactions with

    the coast and poorly planned shoreline development projects can accelerate natural

    erosion rates.

    Sea walls are probably the second most traditional method used in coastal

    management. Modern seawalls aim to re-direct most of the incident energy,

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    resulting in low reflected waves and much reduced turbulence and thus take the form

    of sloping revetments. The most extreme example is that Sea walls at Kamaishi City

    where the world's largest sea wall at a cost of 1.5 billion dollars were built. However,

    after the attack of the recent tsunamis, much of Kamaishi City is now destroyed.

    A major tsunami can have a period of 10 minutes or more and a wavelength of

    100 miles or more, it may pile up and wash over seawalls

    The tsunami creates a strong downpour like flood waters rushing over a dam.

    The seawalls failed catastrophically to protect people and properties. The lesson to

    be learned is that sea walls and engineered structures can protect key facilities if

    they are built high enough and strongly enough, but they cannot be depended on to

    protect large areas in the largest tsunamis or the strongest hurricanes. Water will

    simply pass by well-designed structures that protect key facilities, leaving them

    undamaged. However, large tsunamis and hurricane storm surges can pile up water

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    in front of large sea walls then rush over them like water over a dam.

    When they are needed the most, building larger and stronger sea walls to protect

    large areas would have been too costly to be effective. In the case of the ongoing

    crisis at the nuclear power plants, higher and stronger sea walls should have been

    built if power plants were to be built at that site. However, the Japanese engineers

    made a fundamental design error. They built walls for a far smaller design basis

    earthquake than actually occurred. They built the reactor and sea walls for a

    maximum of M8.2 when this earthquake was M8.9.

    Curved seawalls

    Curved seawalls are designed to enable waves to break to dissipate wave energy

    and to repel waves back to the sea. The curve can also prevent the wave

    overtopping the wall and provides additional protection for the toe of the wall.

    -Concave structure introduces a dissipative element. Curved seawalls aim to re-

    direct most of the incident energy, resulting in low reflected waves and much reduced

    turbulence. The design and construction of curved seawalls are more complicated.

    The deflected waves can scour material at the base of the wall causing them to

    become undermined.

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    Though sea walls are considered strong in holding back waves, they are not always

    reassuring. At Torcross, a new curved seawall was built after an attack of enormous

    storm in 1979. Unfortunately, the following year, another bad storm caused the loss

    of up to five metres of the beachhead along a stretch of beach about 1000 metres in

    length. Part of the motor way ( A379 road) along Slapton Sands near the village was

    also destroyed. The maintenance of the road is imperative to Torcross as it is the

    main access route for the villagers and the local businesses. The South Hams

    District Council tried to keep the A379 from being eroded away by road realignment

    and the importation of shingle from parts of Slapton Sands.

    A study by Natural England after the 2001 storm confirmed that Slapton Sands is and

    will continue to retreat backwards, due to the reduction in the amount of shingle

    available, increasing frequency of storms and a rise in sea level over the next 50

    years.

    Another unsuccessful example happened at the Sandsend, North Yorkshire coast.

    The seawalls were built to redirect the wave energy, however, they failed to do this.

    Instead, energy was absorbed, causing them to brake and damage badly.

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    Generally speaking, seawalls are generally a successful way to control coastal

    erosion but only if they are constructed well with materials that are able to withstand

    the force of ongoing wave energy. Seawalls are considered useful as their usage

    expectancy is much longer than other soft engineering options, and they can

    simultaneously provide recreation opportunities and protection from not everyday

    erosion but that of extreme events. Evaluating the successes and shortcomings of

    seawalls after major natural events may enhance our understandings on their

    weaknesses for future improvement and reassessment.

    Revetment

    Revetments are always made as sloping structures and are very often constructed

    as permeable structures using natural stones or concrete blocks, thereby enhancing

    wave energy absorption and minimising reflection and wave run-up. They may be

    watertight, covering the slope completely or porous to allow water to filter through

    after the wave energy has been dissipated. Revetments can also consist of sand-

    filled geotextile fabric bags, mattresses and tubes. Such structures must be protected

    against UV-light to avoid weathering of the fabric. Sand-bagging is often used as

    emergency protection. Geotextile fabric revetments are fragile against mechanical

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    impact.

    Revetment failure resulting in the exposure of the underlying geotextile layer

    ( Portsmouth Harbour Coastal, UK August 2007)

    A revetment is a passive structure, which protects against erosion caused by wave

    action, storm surge and currents. The main difference in the function of a seawall

    and a revetment is that a seawall protects against erosion and flooding, whereas a

    revetment only protects against erosion. It is used at locations exposed to erosion or

    as a supplement to seawalls or dikes where both erosion and flooding occur. Most

    revetments do not interfere with transport of longshore drift. Since the wall absorbs

    the energy instead of reflecting, erosion of the structure occurs from time to time.

    Major maintenance is required after a period of time. Example of the coastal

    revetments at Portsmouth Harbour (along side the motorway A27) illustrates

    wearing would have occurred after the revetment was built.

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    On site to the east of the A27 A2030 junction. Gaps in the block work

    developed along the revetment where the toe support was insufficient

    Groynes

    Groyne is a physical barrier, is often built at right angles to stop sediment transport in

    the direction of long shore transport. Groyne helps to conserve beach by delaying

    export of material. This type of structure is cheaper as it is often constructed from a

    variety of materials such as wood, rock or bamboo and is normally used on sandy

    coasts. Protection of the shore by use of one groyne only is most often inefficient.

    Therefore, shore protection by groynes is designed as a group comprising from a few

    to tens of individual structures. The main disadvantage of Groynes is that it induces

    local scour at the toes of the structures, causing erosion down drift. Moreover,

    groynes do not protect the beach against storm-driven waves. Groynes are

    considered as cost effective defence measure which requires little maintenance and

    is easily repaired.

    Long shore drift was causing problems at the Clifton Springs Boat Harbour, located

    near Geelong in Victoria, Australia. The sand was following the natural coastal

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    process and was filling up the harbour. This decreases the available drift for boats

    and also increases the maintenance cost. To alleviate this, the City of Greater

    Geelong proposed to construct a groyne, effectively blocking the sand from entering

    the harbour.

    Another successful example; the coastline along the East Coast Park of Singapore,

    where groyne is constructed at the right angles to the beach to prevent material from

    being carried away by longshore drift. It creates J-shaped beaches and thus

    preventing sand from being washed away. This structure has been in place for over

    years, providing protection for the harbour and improvement of beach amenity.

    However, at Sandsend there are groynes made of wood. These groynes cannot

    withstand the waves energy and get damage badly. They have to be changed every

    single year. The waves from the sea would rise onto the groynes causing the wood

    to gradually wear down until they were broken completely.

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    Sea swirling around groynes at Sandsend on the North Yorkshire coast

    Gabions

    Gabion revetments (foregound) are generally preferred to gabion walls (background)

    in coastal environments being less reflective of wave energy and more stable.

    Gabions are wire cages filled with crushed rocks that are piled up along coast e.g.

    gabions are found along the coast in North Norfolk, UK, to reduce coastal erosion.

    However, gabions offer short-term protection because the wire cages are corroded

    by sea water easily and need constant maintenance. It provides short term (5-10

    years) protection from backshore erosion by absorbing wave energy along the dune

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    face. They may be used to direct the force of a flow of flood water around a

    vulnerable structure. Gabions are also used as fish barriers on small streams. Their

    application is restricted to the upper part of sandy beaches, since they are not

    sufficiently durable to withstand regular direct wave action. They should not be

    installed on shingle beaches because wear and tear will rapidly cause damage to the

    baskets. As they are porous structures they will tend to trap wind blown sand and

    allow the growth of vegetation under favourable conditions. Gabions are also easily

    destroyed by excessive trampling. Gabions ruin the natural beauty of coastline,

    therefore gabions may not be appropriate in certain situations.

    Overstrand is at the north coast of Norfolk in England. The gabion embankment

    behind the promenade and retaining wall has been effective in stabilising one section

    of the cliffs. Following the cliff failure at Clifton Way in May 1990, work was

    undertaken to stabilise the site. As a result, surface and sub-surface drains were

    constructed and a large amount of rock armour was used to hold them in place.

    When the channels were first put in, they were put in the wrong places. This rock is

    clearly visible and vegetation was added to the soil at Clifton Way, but the shrubs

    died due to the bad soil condition.

    Rip-Rap

    Large boulders, of 10 tonnes or more, are piled up along the shoreline to form a type

    of sea wall. The rocks are dumped on top of each other leaving gaps between them

    that allow water through. This disperses the energy of the waves and reduces their

    eroding power. The boulders must be large, strong and resistant to erosion. Granite

    and basalt are often used. Small or weak rocks would not be able to withstand the

    impact from the waves and would quickly be eroded. The cost of building this

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    structure is relatively low.

    Building rip-rap walls at Aldeburgh is another approach to dealing with erosion along

    the coastline. These aim to lessen the force of the destructive waves. As the waves

    break on the shore they fail against large boulders or concrete blocks. The many

    gaps in between the blocks help to absorb the energy of the waves.

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    Rrip-rap adjacent to a concrete wall on the Cornish coast runs below a road and

    protects the soft cliff rocks from the sea where the waves hit it at an angle. As the

    coast bends, the wall is replaced by rip-rap that is capable of withstanding the direct

    impact from the waves. The rip-rap is also a less expensive alternative to building a

    longer wall.

    Offshore Breakwaters

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    Offshore breakwaters reduce the intensity of wave action in inshore waters and

    thereby reduce the damage of the coastal erosion. They protect the coast and

    harbor by reducing force of high energy waves before they reach the shore.

    Breakwaters can be built with one end attached to coast or away from coast. The

    breakwaters may be small structures, placed one to three hundred feet offshore in

    relatively shallow water, designed to protect a gently sloping beach. e.g. breakwaters

    can be found along beaches at East Coast Park as well as Siloso Beach on Sentosa

    in Singapore. They will serve to protect the beach there, as erosion has been

    accelerated by the wash from the high-speed ferries plying between the nearby

    World Trade Centre and the Riau islands of Indonesia. However, breakwaters are

    unable to provide complete protection so unprotected parts of the beach will still be

    prone to erosion. therefore breakwaters are not always effective

    The breakwater is placed offshore from and usually parallel

    to the shoreline to protect a shore area from waves

    In 1994 a breakwater was constructed as part of a coast defence scheme at

    Sidmouth in Devon. Sidmouth is a popular holiday destination which depends on it

    shingle beach for both protection from storms and as an am entity for tourists. The

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    severe storms in 1989 and 1990 caused substantial depletion of the beach and

    exposure of the foundations of the seawall.

    A coastal protection scheme comprising of an offshore rock breakwater, rock

    groynes and beach replenishment scheme. The construction works were carried out

    in the winter months to minimize disruption.

    The breakwaters at Sidmouth offer protection from the prevailing south-

    westerly seas

    Beach Nourishment

    This measure requires adding large amount of sand to the beah to replace the ones

    eroded away. This leads to the improvement of the beach quality and storm

    protection. However, this measure is expensive to transport large quantity of sand to

    fill up the beach as sand is continually getting eroded away. Coral reefs also get

    destroyed as the extra sand washed out to sea and covers the corals, depriving them

    of the light which they need to survive.

    Nourishment gained popularity because it preserved beach resources and avoided

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    the negative effects of hard structures. Instead, nourishment creates a soft (i.e.,

    non-permanent) structure by creating a larger sand reservoir, pushing the shoreline

    seaward.

    It is important to note that beach nourishment does not halt erosion, but simply

    provides sediment from an external source, upon which eroding forces will continue

    to act. In this regard, beach nourishment provides a sacrificial, rather than a fixed

    barrier against coastal erosion. Shoreline erosion will continue to occur, but the

    widened and deepened beach will provide a buffer to protect coastal infrastructure

    and other assets from the effects of coastal erosion and storm damage.

    Gold Coast beaches in Queensland Australia have experienced periods of severe

    erosion. In 1967 a series of 11 cyclones removed most of the sand from Gold Coast

    beaches. The Government of Queensland engaged engineers from Netherlands to

    advise them. The recommendations include beach nourishment and an artificial reef.

    It was required to dredge 3,500,000 cubic metres (4,580,000 cu yd) of compatible

    sand from the Gold Coast Broadwater which is delivered through a pipeline to

    nourish 5 kilometers (3.1 mi) of beach between Surfers Paradise and Main Beach.

    The new sand was stabilized by an artificial reef constructed at Narrowneck out of

    huge geotextile sand bags. The new reef was designed to improve wave conditions

    for surfing.

    The cost/benefit ratio was conservatively estimated at 75:1 for a AUS$10million

    investment into beach replenishment. Coastal tourism heavily depends on sun, sea

    and sand. Beach nourishment has the potential to promote recreation and tourism

    through beach widening (Nicholls et al., 2007b). This may serve to enhance pre-

    existing tourism or may serve to attract tourists to the area, thus encouraging

    development. This project is considered as successful as it improves beach amenity,

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    allowing more open space with improved fishing, diving and surfing conditions.

    These help to flourish the tourism market, in return bring along the economic

    benefits.

    In Netherlands, more than one-quarter of the land is below sea level and about 80%

    of the coast consists ofsand dune or beach. The shoreline is closely monitored by

    yearly recording of the cross section at points 250 meters (820 ft) apart, to ensure

    adequate protection. Where long-term erosion is identified, beach nourishment using

    high-capacity suction dredgers is deployed

    Natural Beach (Do nothing)

    In some areas, it is accepted that nothing can be done, and the local authority may

    draw a line to alert the community that building is not allowed and no protection will

    occur. It is a cheap and expedient strategy, which is also considered as very

    environmental friendly, the only pollution produced is from the resettlement process.

    A good example is at Dunwich (South west coastline of England), where low cliffs

    made of soft sands are being eroded, however, there has been no attempt to stop

    this. Many people believe that the only effective way to stop erosion is to allow the

    waves to create a new beach. This would mean losing some of the shore and

    perhaps the village at Dunwich itself. Thus, this Do Nothing approach is not well

    received socially in the local community.

    Another example on Do Nothing approach is from the angle of the ecological and

    wildlife value such as those at Keyhaven and Lymington. The area is low-lying with

    the threat of flooding at times of highest tides or during severe storms. There is a

    growing body of opinion which believes that flooding of certain coastal areas should

    be allowed as a natural event (which would preserve natural habitats) rather than

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    protecting them by expensive schemes. Attempts have been made to protect wildlife

    habitats by creating Nature Reserve and a bird sanctuary, and to encourage

    sustainable tourism by establishing country parks. This is the approach that the New

    Forest Council has explored.

    Managed Retreat

    An alternative option is to move structures and infrastructure inland as the shoreline

    erodes. Retreat is more often chosen in areas of rapid erosion and in the presence of

    little or obsolete development. It is cost effective. It preserves natural coastline and

    probably saves lives. There are no direct costs apart from that of removing any

    defences already in place and maintenance costs are very low.

    Sediment flow is also restored to its natural state, beaches can be naturally

    replenished due to erosion of the coast, providing protection and the balance of the

    coastline returns.

    To the west of the beach at St Margarets at Cliffe, in Kent UK, is a headland made

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    from chalk. Longshore drift is moving sediment from the west towards the east, so

    the pebbles on St Margarets beach will have come from the far side of this cliff.

    The headland projects further out to sea than the beach at St Margarets and thus

    protects the beach to some extent. However, because the headland is subjected to

    the full force of the waves moving in from the west, it is vulnerable to erosion.

    Stabilizing tall cliffs such as these can very difficult and expensive. Preventing these

    cliffs from eroding could also cut off the supply of sediment that is needed to maintain

    the beach.

    This is an example of Managed Retreat. Nature is taking its course and a recent

    rock fall can be seen at the base of the cliff. This approach saves money and helps

    to ensure a supply of sediment for St Margarets beach, but at the cost of losing the

    buildings on the cliff top. Compensation may have to be paid for the loss of the

    buildings.

    Freiston Shore and Abbott's Hall Farm, at Great Wigborough in the Blackwater

    Estuary, it is one of the largest Managed Retreat schemes in Europe. It covers

    nearly 280 hectares of land on the north side of the estuary. As monitoring of the

    managed retreat scheme is lacking, very few sites are effectively monitored and

    evaluated. This hampers the future managed realignment projects.

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    Freiston Shore Managed Realignment site, Lincolnshire

    Conclusions

    Over the years various measures have been developed to defense against flooding

    and erosion. Traditional defences include the building of concrete sea-walls and the

    construction of groynes. Although their main purpose is to prevent material moving

    along the beach, they can help to reduce the effects of breaking waves and by

    widening the beach. However, it is now realized that concrete sea walls, apart from

    being eyesores and at variance with local habitats, absorb rather than reflect wave

    energy. Without constant maintenance and expense, they can be breached. The

    modern approach is to work with nature, rather than against it and to implement

    schemes that are more cost effective, which retain wildlife and which enhance the

    environment. Combining hard and soft engineering measures is sometimes

    necessary to improve the efficiency and provide an environmentally and

    economically acceptable coastal protection system. Hard engineering measures are

    known to be relatively costly and spoil the aesthetic aspect of the beaches or

    coastline. Meanwhile, soft engineering can take time to become effective, and the

    protection may only last for 5 to 10 years, which is rather short term. To optimize the

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    long term positive impact, an integrated approach is preferred (i.e combining hard

    and soft engineering measures). For example, combining beach nourishment and

    groynes ; and rock revetments and groynes. There is evidence that coastal forest

    and trees can play a protective role in coastal erosion. Their clearance has

    increased the vulnerability of coasts to erosion. The vegetation can improve slop

    stability, consolidate sediment and diminish the amount of wave energy moving

    onshore, which should be encouraged.

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