Coastal structures Prepared by Ahmmed Zulfiqar Rahaman
Coastal structuresCoastal structures can be anything human-made in thecoastal area. They are constructed principally to protectthe coast line.
Coastal structures Water resources engineers build these structures to: slow down or prevent coastal erosion (for example, groins and sea walls) increase access or mooring sites (for example, marinas, bridges, causeways and boat ramps) support coastal subdivisions (for example, power poles and storm water pipes)
What willhappen iferosion occurs inthis structure?Lets see……
To escape fromsuch kind oferosion by waveaction coastalstructures areneededindeed……
More than 70 percent of all coastal structures are on theshoreline for protection from probable damage bystorm surge or coastal erosion called Shorelineprotection
Coastal structuresOn the basis of purposesthere are different types ofCoastal structures.They are- RevetmentsBulkheads & sea walls Breakwaters Groins & jetties Coastal bridges & piers Dikes & levees.
Coastal structuresRevetments: Fourth Cliff -Scituate, MARevetments are shorelinestructures constructedparallel to the shoreline.Revetments are structuresplaced on banks or cliffs insuch a way as to absorb theenergy of incoming water orexplosives caused by waterwaves & current.
Coastal structuresRevetments: A cheaper alternative to sea walls is the revetmentUsually built for shore protection Point Allerton -Hull, MA
Revetments:Modern revetments have concrete or shaped blocks ofrip rap stone laid on top of a layer of finer material.Riprap has the advantage of good permeability plus itlooks more natural. Fourth Cliff -Scituate
Coastal structures Revetments components: Armor layer: using armor stone(high wave energy environments) or rip-rap stone(lower wave energy environments) Filter layer: using smaller stone & geo textile fabrics to act as a filter & under layer, which support the armor layer Toe protection prevents under cutting & provides support for all about layer materials.
Coastal structures Bulkheads: Bulkheads are vertical retaining walls to hold or prevent the soil from sliding seawardTimber Bulkhead -Green Harbor Entrance Channel Marshfield
Coastal structures Bulkheads…… secondary purpose is to protect upland areas against damage from wave action.Timber Bulkhead -Green Harbor Entrance Channel Marshfield
Coastal structuresSea walls:form of hard and strong coastal defense constructed on theinland part of a coast to reduce the effects of strong wavesseparate the land & water. Maumeebay (seawall)
Coastal structuresGranite Block Seawall Great Brewster Island Boston Harbor Islands
Coastal structuresCurved or stepped sea walls are designed to enable waveto break and to dissipate wave energy and repel wavesback to the sea. Concrete Seawall Lynn Shore Reservation Lynn
Coastal structures Sea walls:- seawalls are vertical structures constructed parallel along the shore line.- should last 20-30 years. Seawall near Siwash rock in stanely park
Coastal structuresBreakwaters: breakwaters are large scale structures constructed seaward of,& usually to the shore line they attempt to break incoming waves before they reach theshoreline or the facility (e.g. marina) they are protecting .
Coastal structuresSingle breakwaters :Single breakwaters maybe attached ordetached , dependingon what they are beingdesigned to protect
Coastal structuresSingle breakwaters :a single detached breakwaters may protect a smallsection of shorelinea single attached breakwater may a long structureto shelter marines & harbors from wave action.
Coastal structuresHead land breakwaters(HB):-a series of breakwatersconstructed in an “attached”fashion to the shoreline & angledin the direction of predominantwaves-the shoreline behind thestructures evolves into a natural“crenulate” or log spiralembayment.
Coastal structuresDetached breakwaters: detached breakwatersare constructed away fromthe shoreline, usually aslight distance offshorethey are designed topromote beach depositionon their leeside.
Groins: groins are the oldest and most common shore-connected, beachstabilization structurethey help to create or widen beaches by capturing sand movingalong the shoreline. Mortared Stone Groin “The Five Sisters”Broad Sound Winthrop
A groin is an active structure extending from shore intosea, most often perpendicularly or slightly obliquely tothe shoreline
Coastal structures Types of Groins: normal or straight inclined or angled submergedPermeable singlegroin system or fieldT L or Y shapedRubble-mound and sand-filled bagattracting, deflecting or repelling
Coastal structuresCharacteristic of Groins: they are usually made oftropical hardwoods which aremore resistant to marine borersand erosion.a few are made of concrete, steelor in more recent times largerocks.they are spaced about 50-100metres apart.may have a life of 15-20 years
Coastal structuresConcrete groins……. Ukraine ( the black sea)
Coastal structuresShoreline response to groins
Coastal structures Jetties and piers a structure extended into a sea, lake, or river toinfluence the current or tide or to protect a harbor a protecting frame of a pier a landing wharfTimber Pier -George’s Island Boston Harbor Islands
Jetties are shore-normal stone structures commonlyused for training navigation channels & stabilizing inlets
Coastal structuresCharacteristics of jetties:they prevent intrusion of long-shore sediment transport they cause higher flow velocitiesthat scour the channel to a depthrequired for safe navigation.
Coastal structuresCoastal bridges and piers Biloxi bridge
Coastal structuresCoastal bridges and piers Cuba bridge
Coastal structures Dikes & levees dikes are typically earthstructures they keep elevatedwater levels fromflooding interiorlowlands. sometimes they refer toas dam
Coastal structures Gabion:they are stacked to form a simple wall.used to protect a cliff or area in the short term onlygabions have the advantage of ease of use and arerelatively cheap but their life span is short.
Coastal structuresNow-a-days X-block & Tripodal blocks are vastly used forbuilding such coastal structures.
Coastal structures Coastal structures in BangladeshBangladesh has 710 km long coastline
Coastal structures Natural calamities or storm surge visit our country every year So to protect our coastline from wave action or coastal erosion, coastal structures are obviously neededSonadia dip
Coastal structuresThe coastal region of Bangladesh has 123 embanked Coastal structures in Bangladeshpolders, constructed in late sixties to protect the land
Coastal structuresSt. Martin island jetty….. Kutubdia
Coastal structures Importance of coastal structuresCoastal structures are important assets for the economic health ofmany coastal communities to:Protect harbors and inlets that are important commercial andmilitary navigation linksProtect shore-based infrastructureProvide beach and shoreline stability controlStabilize navigation channelsProtect navigation, coastal communities, roadways, bridges, etc.Provide flood protectionProvide recreational activities
Why should we let such coastal area disappear…….???
Coastal structures SummaryCoastal structures influence waves currentssediment transport in the near shoreenvironmentA systematic approach is needed in order tominimize negative effects