Coastal Protection Structures

CONSTRUCTION TECHNOLOGY VI (QSM652) CIVIL ENGINEERING CONSTRUCTION: MARINE CONSTRUCTION COASTAL PROTECTION STRUCTURES Prepared by SITI SARAH MAT ISA Introduction  The coast is always subjected to natural erosion and that erosion caused by man. Wind, waves, currents; and by dredging and construction of structures along the coasts are the main causes of erosions.  These erosions will changed the existing profile of the coasts and create instability to the soil structure along the coasts Introduction  Coastal protection is very important in the Peninsular Malaysia particularly in the east coast.  The east coast is constantly subjected to aggressive natural waves of the South China Sea while the west coast is exposed to the heavily navigated Malacca Strait.  In Malaysia, there is 4900 km of coastline with 29% of it is threatened with erosion. 200km is in critical erosion areas, 235km will be endangered within 5-10 years if no remedial action is taken; and 955km is in areas of acceptable erosion. A Typical Beach Profile Terms and Description Terms Shoreline Coastline Beach (Shore) Description Where land and water meets The line where the coast and the beach meets The area between the mean low water line to the inner edge of the landward limit of effective wave action, normally to the foot of a coastal cliff or to a line of permanent vegetation. The sloping portion of the beach profile lying between the low and high water marks where waves up rush and backwash. The area from the high water shoreline landward to the point of development of vegetation or change in physiographic e.g. cliff, sandbank field etc. Limit of waves during the most severe storm. From the low water mark to the area where bore like translation of waves occur following wave breaking. The sea outwards from near shore The strip of land of indefinite width that extends from the coastline landwards to the first major change in terrain features. the near shore and beach which include the near shore, beach and coast. Foreshore Backshore Near shore Offshore Coast Coastal areas Why coastal protection and sea defense are required? • Marine structures are built to protect the existing and land reclaimed in the near shore and beach and to make those areas more valuable, useful and even beautiful. • Protection from erosion and floods. • Creating a save area for ships, protecting the beach areas Why coastal protection and sea defense are required? • Land reclaimed needs protection in order to maintain its materials from being drifted, washed by the waves and the under currents. • The land reclaimed along the coastal areas are use for many human activities such as for agriculture, settlement, tourism, buildings, transportation and to house maritime activities and structures; and these need to be protected. Coastal Protection Structures The main influencing factors on the choice and the cause of problems in constructing the coastal protection and sea defense systems are: •The nature of the site •High winds and extremely low temperatures •Protection of flora and fauna, etc. •Access to the working areas i.e. the distances from roads, heights and space for machineries •Tides i.e. low and high tides and their occurrences •The conditions of the ground i.e. soft or loose ground as heavy machineries may be required Coastal Management • Changes on sea level have a direct adaptative response from beaches and coastal systems • Coastal zones contain rich resources to produce goods and services and are home to most commercial and industrial activities • When the sea level rises, coastal sediments are in part pushed up by wave and tide energy, so sealevel rise processes have a component of sediment transport landwards. • This results in a dynamic model of rise effects with a continuous sediment displacement that is not compatible with static models where coastline change is only based on topographic data. Coastal Management There are five generic strategies for coastal defense: •Inaction leading to eventual abandonment •Managed retreat or realignment, which plans for retreat and adopts engineering solutions that recognise natural processes of adjustment, and identifies a new line of defence where to construct new defences •Hold the line, shoreline protection, whereby seawalls are constructed around the coastlines •Move seawards, this happens by constructing new defenses seaward the original ones •Limited intervention, accommodation, by which adjustments are made to be able to cope with flood by raising coastal land and buildings vertically Coastal Management The decision to choose a strategy is depend on: • site-specific, • pattern of relative sea-level change, • geomorphological setting, • sediment availability and erosion, • series of social, economic and political factors. Coastal Management • Human strategies on the coast have been heavily based on a static engineered response, whereas the coast is in, or strives towards, a dynamic equilibrium (Schembri, 2009). • Solid coastal structures are built and persist because they protect expensive properties or infrastructures, but they often relocate the problem downdrift or to another part of the coast. • Soft options like beach nourishment, while also being temporary and needing regular replenishment, appear more acceptable, and go some way to restore the natural dynamism of the shoreline. Coastal Management • However in many cases there is a legacy of decisions that were made which have given rise to the present threats to coastal infrastructure and which necessitate immediate shore protection. • For instance, the seawall and promenade (walkway) of many coastal cities in Europe represents a highly engineered use of prime seafront space, which might be preferably designated as public open space, parkland and amenities allow greater flexibility in terms of future land-use change, for instance through managed retreat, in the face of threats of erosion or inundation (flood) as a result of sea-level rise. • Maintenance of those structures or soft techniques can arrive at a critical point (economically or environmental) to change adopted strategy. Coastal Management • Structural or hard engineering techniques • using permanent concrete and rock constructions to "fix" the coastline and protect the assets locate behind. These techniques--seawalls, groynes, detached breakwaters, and revetments--represent a significant share of protected shoreline in Europe (more than 70%). • Soft engineering techniques (e.g. sand/beach nourishments), constructed through natural processes and relying on natural elements such as sands, dunes and vegetation to prevent erosive forces from reaching the backshore. These techniques include beach nourishment and sand dune stabilization. Types of Coastal Protection Structures • The Sea Defense or Coastal Protection structures that are used to protect the land and beach materials from being eroded are : a) Sea walls b) Groynes c) Offshore Breakwaters d) Gabions e) Revetments a)Floodgates b)Beach Nourishment and sand dune stabilization Seawalls Introduction • A seawall is a form of coastal defense constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. • The purpose of a seawall is to protect areas of human habitation, conservation and leisure activities from the action of tides and waves. • As a seawall is a static feature it will conflict with the dynamic nature of the coast and hinder the exchange of sediment between land and sea. Seawalls • Seawalls are classified as a hard engineering shore based structure used to provide protection and to lessen coastal erosion. • However, a range of environmental problems and issues may arise from the construction of a seawall, including disrupting sediment movement and transport patterns • Combined with a high construction cost, this has led to an increasing use of other soft engineering coastal management options such as beach replenishment. Seawalls The many types of seawall in use today depend on: •the varying physical forces they are designed to withstand, •and location specific aspects such as: a.local climate, b.coastal position, c.wave management, d.and value of landform. Seawalls The types of sea wall chosen depends on the circumstances like: 1.the exposure of the site 2.the materials forming the foundation of the wall 3.the existence of a beach in front of the wall and types of beach 4.the cost of the work in relation to the value of the land to be protected Seawalls • Seawalls may be constructed from a variety of materials, most commonly: i. reinforced concrete, ii. boulders, iii.steel, or iv.gabions. • Additional seawall construction materials may include: vinyl, wood, aluminium, fibreglass composite, and with large biodegrable sandbags made of jute and coir Seawalls : Design Principles • A seawall works by reflecting incident wave energy back into the sea, thereby reducing the energy and erosion which the coastline would otherwise be subjected to. • In addition to their unsightly visual appearance, two specific weaknesses of seawalls exist. 1. Firstly, wave reflection induced by the wall may result in scour and subsequent lowering of the sand level of the fronting beach. 2. Secondly, seawalls may accelerate erosion of the adjacent, unprotected coastal areas because they affect the littoral drift process. Seawalls : Design Principles • Fundamentally, a cost-benefit approach is an effective way to determine whether a seawall is appropriate or not and if the negative effects are worth the protection of threatened property. • The design and type of a seawall varies depending on unique aspects specific to each location, and the erosion processes and environment which they are placed in. • There are three main types of seawalls: vertical; curved or stepped; and mounds. Examples of Light Structure Seawall Types of Seawalls Vertical seawalls • Vertical seawalls are built in particularly exposed situations. • These reflect wave energy and, under storm conditions, standing waves will develop. • In some cases piles are placed in front of the wall to lessen wave energy slightly. Vertical seawalls Advantages: Disadvantages: • The first implemented, • These are partial to a most easily designed lot of expensive and constructed type damage in a short of seawall. period of time. • Vertical design can be • Vertical sea walls undercut by high-wave deflect wave energy energy environments away from the coast. over a long period of • Loose rubble can time. absorb wave energy. Curved Seawalls • Curved seawalls are designed to enable waves to break to disperse 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 Curved Seawalls Curved Seawalls Advantages Disadvantages: • The curve can prevent • More complex waves from overtopping engineering and design the wall and provides process. extra protection for the • The deflected waves toe of the wall can scour material at • Curved seawalls aim to rethe base of the wall direct most of the incident causing them to energy, resulting in low reflected waves and much become undermined. reduced turbulence. Mound-type structures Seawalls • Mound-type structures (revetments) are used in less demanding settings where lower energy erosional processes operate. • The least exposed sites involve the lowest-cost bulkheads and revetments of sand bags or geotextiles • These serve to armour (protect) the shore and minimise erosion and may be either watertight or porous, which allows water to filter through after the wave energy has been dispersed Mound-type structures Seawalls Mound-type structures Seawalls Advantages: Disadvantages: • Current designs use • Less durable. porous designs of rock, • Shorter life expectancy. concrete armour. • Cannot withstand or • Slope and loose material protect from highensure maximum energy conditions dispersion of wave energy. effectively. • Lower cost option. Construction of Seawalls There are three main methods used: • The first is thin, interlocking sheet piles driven deeply into the ground. • The second method of seawall construction is individual piles used to support an above-ground structure. • The third method is a massive gravity construction resting on the shore bottom or imbedded slightly in it. This construction is supported by its own weight rather than by piling. Construction of Seawalls Maintenance of Seawalls A seawall may have low maintenance costs if it is properly constructed, but becomes expensive if not. Some possible maintenance costs are: •If no weep holes are installed in the seawall, ground water and rain percolating through the soil will build up pressure behind it, pushing over the wall. •Scouring at the toe of the wall may tip the wall if there is not any toe protection. •Wave energy deflects down the wall, eventually destroying the ends of the wall. •Storms and high tides carrying debris can severely damage the seawall. Groynes Groynes Introduction: • A groyne (groin in the United States) is a rigid hydraulic structure built from an ocean shore (in coastal engineering) or from a bank (in rivers) that interrupts water flow and limits the movement of sediment. • In the ocean, groynes create beaches, or avoid having them washed away by longshore drift. • In a river, groynes prevent erosion and ice-jamming, which in turn aids navigation. Groynes Groynes • Ocean groynes run generally perpendicular to the shore, extending from the upper foreshore or beach into the water. • All of a groyne may be under water, in which case it is a submerged groyne. The areas between groups of groynes are groyne fields. • Groynes are generally made of wood, concrete, or rock piles, and placed in groups. They are often used in tandem with seawalls. Groynes, however, may cause a shoreline to be perceived as unnatural. Groynes • A groyne creates and maintains a wide area of beach or sediment on its updrift side, and reduces erosion on the other. It is a physical barrier to stop sediment transport in the direction of longshore transport • A groyne's length and elevation, and the spacing between groynes is determined according to local wave energy and beach slope. • Groynes that are too long or too high tend to accelerate downdrift erosion because they trap too much sediment. • Groynes that are too short, too low, or too permeable are ineffective because they trap too little sediment • Flanking may occur if a groyne does not extend far enough landward. Groynes • Groynes do not add extra material to a beach, but merely retain some of the existing sediment on the updrift side of the groynes • If a groyne is correctly designed, then the amount of material it can hold will be limited, and excess sediment will be free to move on through the system. • However, if a groyne is too large it may trap too much sediment, which can cause severe beach erosion on the down-drift side. Groynes Groynes can be distinguished by how they are constructed, whether they are submerged, their effect on stream flow or by shape. By construction method Groynes can be permeable, allowing the water to flow through at reduced velocities, or impermeable, blocking and deflecting the current. •Permeable groynes are large rocks, bamboo or timber •Impermeable groynes (solid groynes or rock armour groynes) are constructed using rock, gravel, gabions. Groynes By whether they are submerged • Groynes can be submerged or not under normal conditions. • Usually impermeable groynes are non-submerged, since flow over the top of solid groynes may cause severe erosion along the shanks. • Submerged groynes, on the other hand, may be permeable depending on the degree of flow disturbance needed. Groynes By their effect on stream flow Groynes can be attracting, deflecting or repelling. • Attracting groynes point downstream, serving to attract the stream flow toward themselves and not repel the flow toward the opposite bank. They tend to maintain deep current close to the bank. • Deflecting groynes change the direction of flow without repelling it. They are generally short and used for limited, local protection. • Repelling groynes point upstream; they force the flow away from themselves. A single groyne may have one section, for example, attracting, and another section deflecting. Groynes By shape • Groynes can be built with different plan view shapes. • Examples are straight groynes, T head, L head, hockey stick, inverted hockey stick groynes, straight groynes with pier head, wing, and tail groynes. Types and Shapes of Groynes Types of Groynes Types of Groynes In structural terms, one can distinguish between wooden groynes, sheet-pile groynes, concrete groynes and rubble-mound groynes made of concrete blocks or stones, as well as sand-filled bag groynes. Wooden Groynes •The wooden groynes are most often one- or two-row palisade structures. Effects of influence of the T-shape wooden pile groyne on the shore (local erosion on the lee side and accumulation on the other) •One-row wooden groynes are most often partly permeable structures. This results in reduced erosive lee-side effects and prevents from appearance of semi-closed nearshore water circulations. The wooden palisade groynes are cheap but on the other hand they have low durability. Timber – zig-zag Groynes Timber Groynes Types of Groynes Steel Groynes • Steel groynes are most often constructed of vertical sheet piling, single or double, of various profiles, located perpendicularly to the shoreline. • They are impermeable structures. The experiments have shown that the groynes made of single sheet pile walls are not durable. This is due to corrosion of the material and influence (friction) of the moving sand. • Besides, ice load is very harmful, causing instability and failure of the steel sheet pilings. Mixed massive structures, constituted of steel and concrete, are much more stable and durable. Types of Groynes Concrete Groynes • Groynes built of concrete elements in the form of prefabricated boxes or other reinforced concrete items belong to the most stable and long-lasting coastal structures. • Because of considerable unit weight, the elements composing a groyne of this kind require the existence of suitable soil conditions and the appropriate foundation Types of Groynes Rubble-mound and sand-filled bag groynes • Rubble-mound groynes belong to frequently applied coastal protective structures. • They are built as either loose mounds of stones or mounds of various armour units, e.g. tetrapods. • These groynes are often mixed structures, strengthened inside by the sheet piling. They are relatively massive, durable and impermeable. • The rubble-mound groynes are advantageous with respect to the steel, concrete and wooden ones, as they better disperse energy of waves and currents. Tretrapods coastal protection Types of Groynes Sand-filled bag groynes • The sand-filled bag groynes as a protection measure should rather be considered as a short-term solution. • The bags in a stacked bag groynes can either be sand- or ground-filled. Some additional protection measures are necessary, especially at the groyne head. • A special filter cloth should be used under the bags to reduce settlement in soft bottom. Construction of this type of groynes requires larger bags (heavier than 50 kg), even though they are more difficult to handle and require filling on the spot. Construction of Groynes Construction of Groynes 1. At the beach, sand is first excavated from the area where the groyne will be located. 2. The area is then backfilled with a bedding layer of stone to prevent subsidence of the groyne structure. Using this method of construction, the groyne is extended seawards with bedding material and rock, building up to a level that will permit plant to run on it. 3. As construction progresses to full groyne length manhole rings are used to create voids to take the piles for the walkway that allow public access to the groyne. Groynes construction Construction of Groynes 1. Walkways are independent structures consisting of concrete beams spanning piles driven along the length of the groyne. 2. Walkway sections and pile caps are made at the beach from reinforced precast concrete and lifted into position. 3. Construction proceeds with the head of the groyne being built to its full height. Piles are then driven into position through the voids by a vibrating rig (and air hammer if required). 4. Working shoreward pile heads and walkway sections are put into position at the same time as rock is built up to the finished level. Construction of Groynes 1. The whole operation is then able to retreat off the groyne leaving a near completed structure; just the in situ joints and infill between the walkways and pile heads are completed later. 2. Access ramps are situated between the back of the groynes and the walkway, made from concrete poured in-situ and tied back into the existing stepped seawall. 3. First the wall sections of the ramps are poured, then the ramp is filled with beach sand and the slab section is cast on top. Breakwater Breakwater Introduction: • Breakwaters are structures constructed on coasts as part of coastal defense or to protect an anchorage from the effects of both weather and longshore drift. • Offshore breakwaters, also called bulkhead, reduce the intensity of wave action in inshore waters and thereby reduce coastal erosion or provide safe harborage. • Breakwaters may also be small structures designed to protect a gently sloping beach and placed one to three hundred feet offshore in relatively shallow water. Detached Breakwater at Happisburgh, Norfolk, UK Types of Breakwater • A breakwater structure is designed to absorb the energy of the waves that hit it, either by using mass (e.g., with caissons), or by using a revetment slope (e.g., with rock or concrete armour units). • In Coastal Engineering, a revetment is a land backed structure whilst a breakwater is a sea backed water (water on both sides). • Caisson breakwaters typically have vertical sides and are usually erected where it is desirable to berth one or more vessels on the inner face of the breakwater. They use the mass of the caisson and the fill within it to resist the overturning forces applied by waves hitting them. They are relatively expensive to construct in shallow water, but in deeper sites they can offer a significant saving over revetment breakwaters. Types of breakwater • Rubble mound breakwaters use structural voids to disperse the wave energy. Rock or concrete armour units on the outside of the structure absorb most of the energy, while gravels or sands prevent the wave energy's continuing through the breakwater core. • The slopes of the revetment are typically between 1:1 and 1:2, depending upon the materials used. In shallow water, revetment breakwaters are usually relatively inexpensive. As water depth increases, the material requirements, and hence costs, increase significantly Breakwater Construction • Breakwaters are either constructed some distance from the coast or built with one end linked to it, in which case they are usually called seawalls. • They may be either fixed or floating, the choice depending on normal water depth and tidal range. They usually consist of large pieces of concrete spaced about 50 m apart. • Their design is influenced by the angle of wave approach and other environmental parameters. Breakwater construction can be either parallel or perpendicular to the coast, depending on what will maintain peaceful conditions. Breakwater Construction Breakwater Construction at Jebel Ali, UAE Breakwater Construction Consequences of Breakwater • When oncoming waves hit breakwaters, their erosive power is concentrated on these structures, which are some distance away from the coast. This creates an area of slack water between the breakwaters and the coast. • Sediment deposition can thus occur in these waters and beaches can be built up or extended there. Consequences of Breakwater • Breakwaters also prevent nearby unprotected sections of beaches from receiving fresh supplies of sediments and they may gradually shrink due to erosion in a process known as longshore drift. • On the other hand, breakwaters can also encourage erosion of beach deposits from their base and thus increase longshore sediment transport. • Breakwaters are subject to damage, and overtopping by big storms can lead to big problems with draining any water that gets behind them. Marine structure design at Khor Fakkan, UAE Breakwaters forming entrance at Portland Harbour Gabions Gabions Introduction: • Gabions are cages, cylinders, or boxes filled with rocks, concrete or sometimes sand and soil that are used in civil engineering, road building, and military applications. • For erosion control caged riprap is used. For dams or foundation construction, cylindrical metal structures are used. In a military context, earth or sand-filled gabions are used to protect artillery crews from enemy fire. Gabions Gabions • The most common civil engineering use of gabions is to stabilize shorelines, streambanks or slopes against erosion. • Other uses include retaining walls, temporary floodwalls, silt filtration from runoff, for small or temporary/permanent dams, river training, or channel lining. • 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. Gabions • Gabion baskets have some advantages over loose riprap because of their modularity and ability to be stacked in various shapes; they are also resistant to being washed away by moving water. • Gabions also have advantages over more rigid structures because they can conform to ground movement, dissipate energy from flowing water, and drain freely. • Their strength and effectiveness may increase with time in some cases, as silt and vegetation fill the interstitial voids and reinforce the structure. • They are sometimes used to keep stones which may fall from a cutting or cliff from endangering traffic on a thoroughfare Gabions • GabionsGabions is a strong wire cage with pebbles, stones and rocks inside. • Gabions protect the coast line by stopping the waves hitting the cliffs. it reduces the power of the waves when it hits the small rocks inside the cage. • The advantages: Gabions are made out of natural materials and are very cheap tomake. • Disadvantages: They can take up a lot of space, and when the rocks and stones all erode , the whole cadge will have to be taken away and replaced. Revetment Revetments • Revetments in stream restoration, river engineering or coastal management, they are sloping structures placed on banks or cliffs in such a way as to absorb the energy of incoming water. • 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 minimizing reflection and wave run-up. Revetments Revetments • Revetments can also consist of different kinds of concrete slabs, some of them permeable and interlocking. In this way their functionality is increased in terms of absorption and strength. • Net mesh stone-filled mattresses, such as gabions, are also used; however, they are only recommended for use at fairly protected locations. Revetments • Revetments can also consist of sand-filled geotextile fabric bags, mattresses and tubes. Such structures must be protected against UVlight to avoid weathering of the fabric. Sandbagging is often used as emergency protection. • Geotextile fabric revetments are fragile against mechanical impact and vandalism, and their appearance is not natural. Revetments • A buried revetment can be constructed as part of a soft protection, e.g. as a hard emergency protection built into a strengthened dune which acts as shore protection and/or sea defence. • All types of revetments have the inherent function of beach degradation as they are used at locations where the coast is exposed to erosion. Revetments • A revetment will fix the location of the coastline, but it will not arrest the ongoing erosion in the coastal profile, and the beach in front of the revetment will gradually disappear. • However, as a revetment is often made as a permeable, sloping structure, it will normally not accelerate the erosion, as did seawalls; on the contrary, rubble revetments are often used as reinforcement for seawalls which have been exposed due to the disappearance of the beach. Such reinforcement protects the foot of the seawall and minimizes the reflection. • A revetment, like a seawall, will decrease the release of sediments from the section it protects, for which reason it will have a negative impact on the sediment budget along adjacent shorelines. Beach Nourishment Beach Nourishment • also referred to as beach replenishment or sand replenishment • Beach nourishment is the artificial process of adding sediment to a beach for recreational and aesthetic purposes, as well as to provide a buffer to coastal erosion • describes a process by which sediment (usually sand) lost through longshore drift or erosion is replaced from sources outside of the eroding beach. • A wider beach can reduce storm damage to coastal structures by dissipating energy across the surf zone, protecting upland structures and infrastructure from storm surges, tsunamis and unusually high tides. Beach Nourishment • Beach nourishment is typically part of a larger coastal defense scheme. Nourishment is typically a repetitive process, since nourishment does not remove the physical forces that cause erosion; it simply mitigates their effects. • Nourishment gained popularity because it preserved beach resources and avoided 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 Beach Nourishment Nourishment is required every few years to keep beaches from retreating and the cost is typically millions of dollars per nourishment event. However, the life of the nourishment project can rarely be predicted with accuracy and the costs are high. the existing and increased development at the shoreline are responsible for establishing the need for nourishment, the cost of protecting structures on a retreating shoreline will eventually exceed the value of the property, no matter what type of erosion control is selected Beach ecosystems may be negatively impacted by nourishment. For example, vegetation and animals may be buried by the sand placement The Alaska dredged nearly 783,000 cubic yards of offshore sand for the Ocean Ridge Shore Protection Project Sand was transported from the dredge to the beach by floating and submerged pipe line. Thirty inch pipe discharged up to 60,000 cubic yards of sand per day onto the beach. Bulldozers moved and shaped the sand after it was pumped ashore. The finished project, 1.42 miles long and 200 ft. wide, improves recreational value, provides habitat for protected sea turtles, and protects coastal property from storm damage. … Thank You …