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"GEOMORPHOLOGICAL ASSESSMENT OF TYPE

BUNDS AND THEIR IMPACT ON VARSOLI CREEK,

MAHARASHTRA"

CHAPTER - 1

INTRODUCTION

Coastal and siltation

Coastal erosion is becoming an increasing problem all over the world. Maharashtra State has 720 Km long , which is divided in 5 districts as: 1) Sindhudurg - 120 Km 2) Ratnagiri - 238 Km 3) Raigad - 121 Km 4) Mumbai - 114 Km 5) Thane - 127 Km. Out of the coastal length of 720 Km about 262 Km length is vulnerable to erosion (NCRMP 2008). Major uses of these coastal zones include commercial and industrial development along the coastal belt, human habitation, military defense, extraction of living and non-living resources, recreational facilities, waste disposal, in addition to the construction of port and harbors. For all this development, more and more land along the coastal belt is being used by the humans (NCRMP 2008). The coast represents the meeting point between the land and . are very dynamic areas and they are constantly changing. This change is due to 3 main processes such as erosion, transportation and which operate at the coast. 1) Erosion Natural forces such as wind, and currents are constantly shaping the coastal regions. The landward displacement of the shoreline caused by the forces of waves and currents is termed as . Coastal erosion occurs when wind, waves and longshore currents move from the and deposit it somewhere else. The sand can be moved to another , to the deeper bottom, into an ocean trench or onto the landside of a . The removal of sand from the sand- sharing system results in permanent change in beach shape and structure. The impact of the event is not seen immediately as in the case of or . It is equally important when we consider loss of property. It generally takes months or years for the impact of erosion to be visible. Therefore, this is generally classified as a "long term coastal hazard" (Chambers 2007). 2) Transportation The second process operating at the coast is the material transport. Material eroded by the sea is carried within the in a number of ways, minerals dissolved from rocks are carried in solution, whilst small fragments, light enough to be held within the water, float in suspension. The largest rock fragments which are too heavy to be picked up by the waves, are transported by the process of traction, this is where they roll along the bed when the waves pick up enough energy. Finally, medium sized rock particles, which cannot be carried by the waves all the time, are moved by siltation. This is where during times of higher energy the particles are picked up and then dropped again as the wave looses its energy (Chambers 2007). 3) Deposition Material is moved up the beach by the at an angle which is controlled by the prevailing wind. The backwash then carries material back downs the beach at right angles to the coastline under the influence of gravity. Gradually the material is moved along the coastline, its direction being controlled by the prevailing wind direction. The final process operating at the coast is that of deposition. This is where material that is too heavy to be transported any more is left behind, building up the beach. Due to the importance of energy in transporting sand and shingle, it is the largest material that is deposited first (Chambers 2007). Material that is transported by the waves along a coastline is eventually deposited forming distinctive deposition features. There are four main depositional features developed on coasts. These are , spits, bars, . Beaches are the main feature of deposition found at the coast. These consist of all the material (sand, shingle etc.) that has built up between the high and low mark. There are number of different sources of beach material, the main source being , where fine and are deposited at the mouth. Other sources of beach material include (bringing material from elsewhere along the coast), constructive waves (bringing material up the beach from the sea) and from erosion. Erosion is the most significant process on the coast. It works as follows : - a) Corrasive action Waves equipped with sand, and perform erosive work. Hurling of sand, shingle and boulders against the cliffs are destructive in action. These have abrasive effect. It is physical erosion caused by loose solid material during its journey. Vertical and lateral corrasion occurs on the coast. Undercutting the coastal rocks pave out into caves. Finally the ceiling of the cave collapses and the rock mass is eroded. Collapsing of the cave roof or overhanging cliff is assisted by weathering or sub aerial erosion, pull of gravity, structural weaknesses and rain action (Singl998). b) Attrition The pieces of beach material as they are thrown up against sea rocks, they are swirled up and down the beach. Due to swash and backwash of waves rock fragments are repeatedly hitted within each other and get broken and ground up. This is known as attrition. It mainly occurs due to coalescence of eroded particles among each other. c) Hydraulic action The waves that attack against cliffs and sea walls put pressure upon the coast. At the time of breaking of the waves against cliff face the air in gaps, cracks, crevices is locked up, it gets compressed and this high pressure acts like a wedge, forcing the gap and side walls apart. With the backwash the pressure is released and compressed air expands again. The compression and expansion of the air in the cracks and gaps alternate repeatedly so that, rocks are weakened and cavities are enlarged by hydraulic action. d) Solvent action Solvent action denotes chemical reaction of sea water and corrosion effects. Sea water with dissolved chemicals induces solvent action. Rocks like chalk and limestone are eaten by solvent action of sea water. Following are the major natural factors of coastal erosion :- 1) Waves Waves are generated by offshore and nearshore winds, which blow over the sea surface and transfer their energy to the water surface. As they move towards the shore, waves break and the turbulent energy released stirs up and moves the deposited on the . The wave energy is a function of the wave heights and the wave periods (Chambers 2007). 2) Wind Wind acts not just as a generator of waves but also as a factor of the landward movement of which is necessarily aeolian erosion. 3) Tides result in the water elevation of water surface due to the attraction of water masses by the moon and the sun. During high tides, the energy of the breaking waves is released higher on the foreshore or the cliff base (cliff undercutting). 4) Near-shore currents Sediments scoured from the seabed are transported away from their original location by currents. In turn the transport of coarse sediments defines the boundary of coastal cells, i.e. relatively self contained system within which coarse sediments stay. Currents are generated by the action of tides (ebb and flood currents), waves breaking at an oblique angle with the shore (longshore currents), and the backwash of waves on the foreshore (rip currents). All these currents contribute to coastal erosion processes (Chambers 2007). 5) Storms Storms result in raised water levels (known as storm surge) and highly energetic waves induced by extreme winds (Cyclones). Combined with high tides, storms may result in catastrophic damages. Beside damages to coastal infrastructure, storms cause beaches and dunes to retreat by tenths of meters in a few hours, or may considerably undermine cliff stability. 6) Catastrophic events In addition to the daily, slow erosion of the coast, other events like result in major coastal changes over very short time periods. These are referred to as catastrophic events because of the extensive damage that is caused and the unpredictable nature of the event. 7) Slope processes The term "slope processes" encompasses a wide range of land-sea interactions which eventually result in the collapse, slippage, or topple of coastal cliff blocks. These processes also involve terrestrial processes such as rainfall and water. 8) Vertical land movements (compaction) Vertical land movement including isostatic rebound, tectonic movement, or sediment deposition may have either a positive or negative impact on coastline evolution. Problem of coastal erosion and deposition Coastal erosion is becoming an increasing problem all over the world. Before finding solution to stop the erosion at a specific location, the cause of erosion must be found at that location. Therefore it is important to understand how sediment is removed and transported. The different types of erosion may be split up into two groups. 1) Erosion due to natural causes 2) Erosion resulting from human interference (Perdok 2002). The problem of erosion calls for the protection of houses, cultivable lands, valuable properties, monuments etc. in the coastal belt. It is well known that the erosion of a coast is mainly due to action of waves in addition to the currents setup by the oblique attack of waves. Erosion of the coast depends on many natural factors like storm waves, nature of the beach, beach material and the shape of the coast, tidal level changes, movement and quantity of the littoral drift material. Storms may occur seasonally, sand spits may grow in a few decades and the rise that involves centuries. The various natural causes have different time scales. The best natural defense against erosion is however an adequate beach on which waves expends their energy. Waves are the prime cause of beach erosion; it is natural that the protective methods are evolved so as to dissipate the energy of waves either by absorbing this energy on the beach or dissipating / diverting the same before the waves approach the beach. The erosion due to human activities may include the removal of beach material, changing direction of sediment movement etc. The process of coastal erosion after a certain time finds an equilibrium stage by redistributing sediment along the shorelines. To identify the cause of erosion at a certain location, the problem area itself must be investigated, along with a much larger area along the neighboring coast (Perdok 2002). and deposition Sediment transport plays an important role in many problems. If the volume of sand that enters an area is smaller than the volume that leaves the area, erosion takes place. On the other hand, accretion will occur if more sediment is brought into the area than that which leaves the area. In a coastal zone both waves and currents are of importance for the sediment transport. The total transport in a certain direction is found by adding up the transport at each level in the water. As the transport largely differs at each level, it is difficult to measure the precise amount of sediment transport. In general the sediment transport processes can be divided into three stages - 1) The stirring-up or the loosening of bottom material 2) The horizontal displacement of these particles by the water 3) The re-sedimentation of these particles Each stage depends on the water movement and the sediment characteristics. The water movement is basically different for currents, waves, or for both waves and currents together. Important factor in sediment transport is the nature of sediments. The main characteristics of sediments are the diameter and the mass density. When water flows over a beach, the currents cause horizontal and vertical movement of particles. In order to initiate a sediment transport, the fluid stresses have to overcome the particles' threshold of movement. Obviously shingle has a larger threshold of movement than sand (Perdok 2002). The horizontal displacement may be divided into three modes of transport. 1) Bed load 2) Suspended load 3) Sheet flow. Mode of transport is primarily dependent on the intensity of water movement. Generally at first there will only be bed load, and small ripples will start to form. If the velocity of the water increases, the ripples will increase in size and particles will be brought into suspension. If the increases even more, the ripples will be washed away, resulting in sheet flow. The difference between the various modes of transport is difficult to define, and often both the lower, or higher modes take place simultaneously (Perdok 2002). Coastal regions are the most dynamic zones where the effects of these processes are immediately reflected in the morphological characteristics of the region. Beaches are the constantly changing features. They change over hourly, daily and yearly time-periods. Any sea defenses built on or near the beach influence the natural processes. Sea defense may result in beach accretion or erosion, or both of these on different parts of the beach. Sometimes, the changes may be seen just months after the structure is built. There are three main groups of solid structures, which protect land or beaches. 1) Structures built parallel to the shore (, bulkheads, ) 2) Structures built at right angles to the shore ( and ) 3) Offshore structures like offshore breakwaters. When waves approach the shoreline at angle, they generate a longshore current which transports sand suspended in the water along the shore. In addition, the wave generated turbulence carries sand up the beach face in the general direction of wave approach. As the water returns seaward, it moves directly down the beach face in response to gravity. Thus, sand moves along the beach face in a zig - zag motion. Structures designed to trap this moving sand are called groynes. A groyne is a method of coastal defense against erosion. They are the structures running perpendicular to the shoreline. They go across a beach and into the sea. The effect of a groyne is to accumulate sand on the updrift side where longshore drift is predominantly in one direction. They are effective at causing the deposition of beach material on one side. Groynes are extremely cost-effective coastal defense measures, requiring little maintenance. However, groynes are increasingly viewed as detrimental to the aesthetics of the coastline, and there is a strong opposition to such structures in many coastal communities. Coastal protection measures and methods Coastal protection measures are usually divided into two groups. 1) 2) . Hard engineering means the building of structures that could prevent erosion, such as , breakwaters, groynes, , revetment, offshore breakwaters, walls, beach drains, and rock armour. Hard engineering options tend to be expensive and short-term options. They may also have a high impact on the landscape or environment. Soft engineering is a cheaper option than hard engineering. They are usually also more long -term and sustainable, with less impact on the environment. In this method , dune construction, planting mangroves, encouraging the growth of coral reefs are included (USAGE 2002). Coastal protection methods are used to protect coastal lands from erosion. Beaches can exist only where a delicate dynamic equilibrium exists between the amount of sand supplied to the beach and the inevitable losses caused by wave erosion. Coastal structures are mainly used in coastal defense schemes with the objective of preventing shoreline erosion and flooding of the hinterland. Other objectives include sheltering of harbor basins and harbor entrances against waves, stabilization of navigation channels and , and protection of water intakes and outfalls. The coastal protection measures often used are as given below - A) Hard engineering methods 1) Groynes Groynes are built to stabilize a stretch of natural or artificially nourished beach against erosion that is due primarily to a net longshore loss of beach material. Groynes function only when longshore transport occurs. Groynes are narrow structures, usually straight and perpendicular to the preproject shoreline. The effect of a single groyne is accretion of beach material on the updrift side and erosion on the downdrift side; both effects extend some distance from the structure. Consequently, a groyne system (series of groyne) results in a saw -tooth-shaped shoreline within the groyne field and a differential in beach level on either side of the groynes (USAGE 2002) (Figure 1.1). Groynes create very complex current and wave patterns. However, a well- designed groyne system can arrest or slow down the rate of longshore transport and, by building up of material in the groyne bays, provide some protection of the coastline against erosion. Groynes are also used to hold artificially nourished beach material, and to prevent sedimentation or accretion in a downdrift area (e.g., at an ) by acting as a barrier to longshore transport. Deflecting strong tidal currents away from the shoreline might be another purpose of groynes.

Groyne

Original shoreline

(After Chua 2013) Figure 1.1

The orientation, length, height, permeability, and spacing of the groynes determine, under given natural conditions, the actual change in the shoreline and the beach level. Because of the potential for erosion of the beach downdrift of the last groyne in the field, a transition section of progressively shorter groynes may be provided to prevent the formation of a severe erosion area. Even so, it might be necessary to protect some part of the downdrift beach with a seawall or to nourish a portion of the eroded area with beach material from an alternative source. Groynes are occasionally constructed non-perpendicular to the shoreline, can be curved, have fishtails, or have a shore-parallel T-head at their seaward end. Also, shore-parallel spurs are provided to shelter a stretch of beach or to reduce the possibility of offshore sand transport by rip currents. However, such refinements, compared to the simple shape of straight perpendicular groynes, are generally not deemed effective in improving the performance of the groynes. In most cases, groynes are sheet-pile or rubble-mound constructions. The latter is preferably used at exposed sites because of a rubble-mound structure's ability to withstand severe wave loads and to decrease wave reflection. The landward end of the groynes must extend to a point above the high-water line in order to stay beyond the normal zone of beach movement and thereby avoid outflanking by back scour. The groynes must, for the same reason, reach seawalls when present or connect into stable back beach features. The position of the seaward end is determined such that the groyne retains some proportion of the longshore transport during more severe wave conditions. This means that the groyne must protrude some distance into the zone of littoral transport, the extent of which is largely determined by width. Groynes can be classified as either long or short, depending on how far across the surf zone they extend. Groynes that transverse the entire surf zone are considered long, whereas those that extend only for a part limited the surf zone are considered short. These terms are relative, since the width of the surf zone varies with water level, , and beach profile. Most groynes are designed to act as short structures during severe sea conditions and as long structures under normal conditions. Groynes might also be classified as high or low, depending on the possibility of sediment transport across the crest. Significant cost savings can be achieved by constructing groynes with a variable crest elevation that follows the beach profile rather than maintaining a constant crest elevation. These groynes would maintain a constant cross section and allow increasing amounts of sand to bypass as water depth increases. At some point the crest of the groyne becomes submerged.

10 Terminal groynes extend far enough seaward to block all littoral transport, and these types of groynes should never be used except in rare situations, such as where longshore transported sand would be otherwise lost into a submarine . Some cross-groyne transport is beneficial for obtaining a well-distributed retaining effect along the coast. For the same reason permeable groynes, which allow sediment to be transported through the structure, may be advantageous. Examples of permeable groynes include rubble-mound structures built of rock and concrete armor units without fine material cores, and structures made of piles with some spacing. Most sheet-pile structures are impermeable. Low and permeable groynes have the benefit of reduced wave reflection and less formation compared with high and impermeable groynes (USAGE 2002) (Plate 1.1).

Low Groynes

(After Winter 2008) Plate

2) Seawalls Seawalls are onshore structures with the principal function of preventing or alleviating overtopping and flooding of the land and the structures behind due to storm surges and waves. Seawalls are built parallel to the shoreline as a reinforcement of a part of the coastal profile. Quite often seawalls are used to protect promenades,

11 roads, and houses placed seaward of the crest edge of the natural beach profile. Seawalls range from vertical face structures such as massive gravity concrete walls, tied walls using steel or concrete piling, and stone-filled cribwork to sloping structures with typical surfaces being reinforced concrete slabs, concrete armor units, or stone rubble. Erosion of the beach profile landward of a seawall might be stopped or at least reduced. However, erosion of the seabed immediately in front of the structure will in most cases be enhanced due to increased wave reflection caused by the seawall. This results in a steeper seabed profile, which subsequently allows larger waves to reach the structure. As a consequence, seawalls are in danger of instability caused by erosion of the seabed at the toe of the structure, and by an increase in wave slamming, runup, and overtopping. Because of their potential vulnerability to toe scour, seawalls are often used together with some system of beach control such as groynes and beach nourishment (USAGE 2002) (Plate 1.2).

Seawalls

•J«

(After Wallingford, Brampton, George, Coates 2000)

3) Gabions Gabions is a strong wired fence filled with rocks and pebbles (Plate 1.3). Gabions protect the cliffs by stopping the wave crashing and eroding the cliffs. The

12 advantages are that it helps to protect the coast hne by stopping the waves pounding at the cHffs. It does this by breaking the power of the waves when it hits the little rocks inside the cage. Gabions are quite natural as rubble or pebbles can be used. Gabions are used to protect a cliff or area in the short term only, since they are easily damaged by powerful storm waves and the cages tend to rust quite quickly. Gabions are relatively cheap but their life span is short (USAGE 2002).

Gabions

(After Edom, Street, Cunninghum, Davis, Freemantle 2005) plate 1.3

4) Revetments are onshore structures with the principal function of protecting the shoreline from erosion. Revetment structures typically consist of a cladding of stone, concrete, or asphalt to armor sloping natural shoreline profiles (Plate 1.4). In river engineering or revetments are sloping structures placed on banks or cliffs in such a way as to absorb the energy of incoming water. In military engineering they are structures, again sloped, created to secure an area from artillery, bombing, or stored explosives. In architecture they are a variety of structures, normally vertical, used to retain a wall, or sometimes just to decorate it.

13 River or coastal revetments are usually built to preserve the existing uses of the shoreline and to protect the slope, as defense against erosion (USAGE 2002).

Revetments

(After Wallingford, Brampton, George, Coates 2000) | Platel.4~|

5) Jetties Jetties are used for stabilization of navigation channels at river mouths and tidal inlets. Jetties are shore-connected structures generally buiU on either one or both sides of the navigation perpendicular to the shore and extending into the ocean (Plate 1.5). By confining the stream or tidal flow, it is possible to reduce channel shoaling and decrease dredging requirements. Moreover, on coastlines with longshore currents and littoral drift, another function of the jetties is also to arrest the crosscurrent and direct it across the entrance in deeper water where it represents less hazard to navigation. When extended offshore of the breaker zone, jetties improve the maneuvering of ships by providing shelter against storm waves. Jetties are constructed similar to breakwaters (USAGE 2002).

14 Jetties

(After Aurofillo 2010)

6) Breakwaters Breakwaters are built to reduce wave action in an area in the lee of the structure. Wave action is reduced through a combination of reflection and dissipation of incoming wave energy. When used for harbors, breakwaters are constructed to create sufficiently calm for safe and loading operations, handling of ships, and protection of harbor facilities. Breakwaters are also built to improve maneuvering conditions at harbor entrances and to help regulate sedimentation by directing currents and by creating areas with differing levels of wave disturbance. Protection of water intakes for power stations and protection of coastlines against tsunami waves are other applications of breakwaters. When used for shore protection, breakwaters are built in nearshore waters and usually oriented parallel to the shore like detached breakwaters (Plate 1.6). The layout of breakwaters used to protect harbors is determined by the size and shape of the area to be protected as well as by the prevailing directions of storm waves, net direction of currents and littoral drift, and the maneuverability of the vessels using the harbor. Breakwaters protecting harbors and channel entrances can be

15 either detached or shore-connected. The cost of breakwaters increases dramatically with water depth and wave climate severity. Also poor foundation conditions significantly increase costs. These three environmental factors heavily influence the design and positioning of the breakwaters and the harbor layout. Breakwaters can be classified into two main types - 1) sloping-front 2) vertical-front structures. Sloping-front structures are in most cases rubble-mound structures armored with rock or concrete armor units, with or without wave wall superstructures. Vertical-front structures are in most cases constructed of either sand filled concrete caissons or stacked massive concrete blocks placed on a rubble stone bedding layer. In deep water, concrete caissons are often placed on a high mound of quarry rock for economical reasons. These breakwaters are called composite structures. The upper part of the concrete structure might be constructed with a sloping front to reduce the wave forces. For the same reason the front wall might be perforated with a wave chamber behind to dissipate wave energy. Smaller vertical structures might be constructed of steel sheet piling backfilled with soil, or built as a rock-filled timber cribwork or wire cages (USAGE 2002).

Breakwaters

(After Wallingford, Brampton, George, Goates 2000) Plate 1.6

16 7) Bulkheads Bulkhead is the term for structures primarily intended to retain or prevent sliding of the land, whereas protecting the hinterland against flooding and wave action is of secondary importance. Bulkheads are built as soil retaining structures, and in most cases as a vertical wall anchored with tie rods. The most common application of bulkheads is in the construction of mooring facilities in harbors and marinas where exposure to wave action is minimized (USAGE 2002) (Plate 1.7). Bulkheads are normally constructed in the form of a vertical wall built in concrete, stone, steel or timber. Bulkheads are normally smaller than seawalls (Mangor, Karsten 2007).

Bulkheads

(After Brad 2012)

8) Sea dikes Sea dikes are onshore structures with the principal ftinction of protecting

17 low-lying areas against flooding. Sea dikes are usually built as a mound of fine materials like sand and with a gentle seaward slope in order to reduce the wave run-up and the erodible effect of the waves (Plate 1.8). The surface of the dike is armored with grass, asphalt, stones, or concrete slabs (USAGE 2002).

Sea dikes

(After Jackson 2012) Plate 1.81

9) Detached breakwaters Detached breakwaters are small, relatively short, nonshore-connected nearshore breakwaters with the principal function of reducing beach erosion (Plate 1.9). They are built parallel to the shore just seaward of the shoreline in shallow water depths. Multiple detached breakwaters spaced along the shoreline can provide protection to substantial shoreline frontages. The gaps between the breakwaters are in most cases on the same order of magnitude as the length of one individual structure. Each reflects and dissipates some of the incoming wave energy, thus reducing wave heights in the lee of the structure and reducing shore erosion. Beach material transported along the beach moves into the sheltered area behind the breakwater where it is deposited in the lower wave energy region. The nearshore

18 wave pattern, which is strongly influenced by diffraction at the heads of the structures, will cause salients and sometimes tombolos to be formed, thus making the coastline similar to a series of pocket beaches. Once formed, the pockets will cause wave refraction, which helps to stabilize the pocket-shaped coastline. Like groynes, a series of detached breakwaters can be used to control the distribution of beach material along a coastline. Just downdrift of the last breakwater in the series there is an increased risk of shoreline erosion. Detached breakwaters are 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. Properly designed detached breakwaters are very effective in reducing erosion and in building up beaches using natural littoral drift. Moreover, they are effective in holding artificially nourished beach material (USAGE 2002).

Detached breakwaters

(After Deborah 2011) Plate 1.9

19 10) breakwaters Reef breakwaters are coast-parallel, long or short submerged structures built with the objective of reducing the wave action on the beach by forcing wave breaking over the reef (Plate 1.10). Reef breakwaters are normally rubble-mound structures constructed as a homogeneous pile of stone or concrete armor units. The breakwater can be designed to be stable or it may be allowed to reshape under wave action. Reef breakwaters might be narrow crested like detached breakwaters in shallow water or, in deeper water; they might be wide crested with lower crest elevation like most natural reefs that cover a fairly wide rim parallel to the coastline. Besides triggering wave breaking and subsequent energy dissipation, reef breakwaters can be used to regulate wave action by refraction and diffraction. Reef breakwaters represent a nonvisible hazard to swimmers and boats (USAGE 2002).

Reef breakwaters

(After Setz, Molly 2010) Plate 1.10

11) Submerged sills A submerged sill is a special version of a reef breakwater built nearshore and used to retard offshore sand movements by introducing a structural barrier at one

20 point on the beach profile (Plate 1.11). However, the sill may also interrupt the onshore sand movement. The sill introduces a discontinuity into the beach profile so that the beach behind it becomes a perched beach as it is at higher elevation and thus wider than adjacent beaches. Submerged sills are also used to retain beach material artificially placed on the beach profile behind the sill. Submerged sills are usually built as rock-armored, rubble-mound structures or commercially available prefabricated units. Submerged sills represent a nonvisible hazard to swimmers and boats (USAGE 2002).

Submerged sills

(After Carl 2013)

12) Beach drains Beach drains are installed for the purpose of enhancing accumulation of beach material in the drained part of the beach (Plate 1.12). In principal, the drains are arranged at an elevation just beneath the lowest seasonal elevafion of the beach profile in the swash zone. Pumping water from the drains causes local lowering of the groundwater table, which helps reduce the backwash speed and the groundwater outflow in the beach zone. This allows more beach material to settle out on the

21 foreshore slope. Beach drains are built like normal surface drain systems consisting of a stable granular filter, with grain sizes ranging from that of the beach material to coarse materials like pebbles, arranged around closely spaced perforated pipes. The drain pipes are connected to few shore-normal pipelines leading to a pump sump in the upper part of the beach profile. Replacing the granular filter with geotextiles is not recommended because of the increased tendency to clog the drainage system (USAGE 2002).

Beach drains

« - ^ . -> - -4^., r ^Rs^^Sr^^^^^^ (After Mira 2012) Plate 1.12

13) Floating breakwaters Floating breakwaters represent an alternative solution to protect an area from wave attack, compared to conventional fixed breakwaters (Plate 1.13). It can be effective in coastal areas with mild wave environment conditions. Therefore, they have been increasingly used aiming at protecting small craft harbours or marinas or, less frequently, the shoreline, aiming at erosion control. Floating breakwaters might be a proper solution where poor foundations possibilities prohibit the application of bottom supported breakwaters. In water depths in excess of 6 m, bottom connected

22 breakwaters are often more expensive than floating breakwaters. Floating breakwaters present a minimum interference with water circulation and fish migration. Floating breakwaters have a low profile and present a minimum intrusion on the horizon, particularly for areas with high tide ranges. Floating breakwaters can usually be rearranged into a new layout with minimum effort. Floating breakwaters are very effective when their width is of order of half the wavelength or when their natural period of oscillafion is much longer compared to the wave period (USAGE 2002).

Floating breakwaters

(After Ruol 2008)

14) Scour protection The function of scour protection of the seabed is to prevent instability of coastal structures with foundations that rely on stable seabed or beach levels. Both granular material and clay can be eroded by the action of waves and currents. Scour potential is especially enhanced by a combination of waves and currents. In most cases scour protection consists of a rock bed on stone or geotextile filter; however, several specially designed concrete block and mattress systems exist. Scour protecfion is commonly used at the toe of seawalls and dikes; and in some instances scour

23 protection is needed around piles and pillars, at the toe of vertical-front breakwaters, and at groyne heads. Scour protection might also be needed along structures that cause concentration of currents, such as training walls and breakwaters extending from the shoreline. Highly reflective structures like impermeable vertical walls are much more susceptible to near structure scour than sloping rubble-mound structures. (USAGE 2002) (Plate 1.14).

Scour protection

(After Verhagen 2013)

15) Storm surge barriers Storm surge barriers protect against storm surge flooding and related wave attack. These barriers also prevent excessive intrusion of salt-water wedges during high-water episodes. In most cases the barrier consists of a series of movable gates that normally stay open to let the flow pass but will be closed when storm surges exceed a certain level. The gates are sliding or rotating steel constructions supported in most cases by concrete structures on pile foundations. Scour protection on either side of the barrier sill is an important part of the structure because of high flow velocities over the sill (USAGE 2002) (Plate 1.15).

24 storm surge barriers

(After Craven 2013)

16) Pile structures The most common pile structures in coastal engineering are bridge extending from the shore into the water where they are exposed to loads fi-om waves, currents, and in cold regions, ice loads (Plate 1.16). The purpose of pile structures might be to provide open coast moorings for vessels, in which case the deck and the piles must carry loads from traffic, cranes, goods, and pipeline installations. The supporting pile structure might consist of slender wood, steel or reinforced concrete piles driven into the sea-bed, or of large diameter piles or pillars placed directly on the seabed or on pile work, depending on the bearing capacity and settlement characteristics of the seabed. Large diameter piles would commonly be constructed of concrete or be steel pipes filled with mass concrete. Pillars would most commonly be constructed as concrete caissons, concrete block work, or backfilled steel sheet piling (USAGE 2002).

25 Pile structures

(After Jason 2013)

17) Training walls Training walls are structures built to direct flow (Plate 1.17). Typical training wall objectives might be to improve mooring conditions in an or to direct littoral drift away from an area of potential deposition. Most training walls are constructed using sheet piles (USAGE 2002).

Training walls

(After Gillian 2012)

26 B) Soft engineering methods 1) Beach nourishment Beach nourishment is a soft structure solution used for prevention of shoreline erosion. Material of preferably the same, or larger, and density as the natural beach material is artificially placed on the eroded part of the beach to compensate for the lack of natural supply of beach material (Plate 1.18). The beach fill might protect not only the beach where it is placed, but also downdrift stretches by providing an updrift point source of sand (USAGE 2002).

Beach nourishment

(After Wallingford, Brampton, George, Goates 2000) Plate 1.18

2) Dune construction Dune construction is the piling up of beach quality sand to form protective dune fields to replace those washed away during severe storms (Plate 1.19). An essential component of dune reconstruction is planting of dune vegetation and placement of netting or snow fencing to help retain wind-blown sand normally trapped by mature dune vegetation. Storm over wash fans may be a viable source of material for dune construction (USAGE 2002).

27 Dune construction

(After Wallingford, Brampton, George, Coates 2000) Plate 1.19 3) Planting of mangroves Planting mangroves along the shore (Plate 1.20). Mangroves with their prop roots help trap sediments and reduce coastal erosion. As mangrove communities grow seawards, they extend the coastal land seawards. It can affect the depth of coasts and has implications for port activities/coastal transportation. However, young mangroves are very vulnerable, thus the help of the local people is needed to help take care for these plants.

Planting of mangroves

(After Cleveland 2010) Plate 1.20

28 4) Encouraging growth of coral reefs Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny animals found in marine waters that contain few nutrients. Coral reefs are masses of rock like substance called corals growing in shallow water. They protect beaches against coastal erosion by reducing the speed of the waves approaching the coast. Resulting the waves losing most of their energy. Negative impact of this method is human activities like dynamite fishing and destroyed coral reefs, water pollution affected the growth of reefs (Plate 1.21).

Encouraging growtli of coral reefs

(After Wijgerde, Houlbreque, Ferrier 2008) Plate 1.21

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