FOR NCBOC CL-01-10NCBTC, NCBDE

CAPT LORENZO I ADECER PN(RET)

(LECTURER)

LT DANTE P ARELLANO PN

(COURSE DIRECTOR)

WATERFRONT STRUCTURES andDREDGING OPERATIONS

Definition of Waterfront Structure

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Is a contained land areaor a structure that lies alongside a body of water

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Waterfront Structure is divided

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Off shore Structures –designed to create a sheltered Harbor.

Example: Breakwater

Breakwater is an offshore barrier, erected to break the action of the waves and thereby maintain an area of calm water inside.

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A JETTY is a similar structure, except that its main purpose is to direct a current or tidal flow along the line of selected channel

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Composition of a Rubble-mound or rock-mound breakwater

• Cap Rock - is the largest rock placed at the top

• Class A Rock – is a rock not less than 85% of which consists of pieces weighing more than 2 tons each

• Class B Rock – is a rock not less than 60% of which consists of pieces weighing of more than 100 Lbs each , but less than 2 tons

• Class C Rock - also called quarry waste, is any rock smaller than class B

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Composite Breakwater

• Is a breakwater intended for a deep-water site, or for one with an extra-high tide range. It is a rubble – mound breakwater topped with a concrete cap structure

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Along Shore Structure – designed to establish a definite shoreline and

maintain it against wave erosion

Example: Seawalls

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Seawalls

• It is a vertical or a sloping wall which offers protection to a section of the shoreline against erosion and slippage due to tide and wave action

• Seawalls are classified according to the type of construction: Riprap or a solid concrete

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Wharfage Structures – designedto make it possible for ships to lie

alongside for loading and discharging.

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Types of Wharfage Structures

• Quay• Square Pier• Right Angle Pier for one freighter on

each side• Right Angle for one freighter and lighter

on each side• Acute- angle pier for one freighter on

each side

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Type of Wharfage Structure

• Right –Angle Pier for two freighters on each side

• Acute – Angle pier for two freighters on each side

• T- type Marginal Wharf for freighter on outer birth and lighter on inner birth

• U – Type Marginal Wharf

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Bulkheads

• Used in port construction, is a vertical retaining structure used along a shore or the shore end of a pile wharf or approach, its purpose is to support and protect from erosion an area of shore or fill

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Classified According to Type of Construction:

• Pile and Sheathing Bulkhead

• Wood sheet-pile bulkhead

• Steel sheet-pile bulkhead

• Concrete sheet-pile bulkhead

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DREDGING OPERATIONS

What is Dredging ?

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Dredging is an operation to excavate material from the bottom of a shallow sea or freshwater area, disposing of the materials at a different location

Dredging is an operation to excavate material from the bottom of a shallow sea or freshwater area, disposing of the materials at a different location

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The process of Dredging may involve scraping or sucking the seabed and

the dredged materials are called Spoils

• The machinery for dredging is called Dredge

• A ship or boat equipped with dredge is called a Dredger

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Primary Uses of Dredging• To create a new harbor or water ways• To maintain navigable waterways or channel• Make preparations for future docks and bridges• Dredged materials may be used to construct new

land elsewhere for flood or erosion control• Historically, dredging has been used for gold mining

and other valuable substances• Dredging may also be used to remove trash and

debris, and to reclaim areas affected by toxic chemicals and urban run off.

Dredging however may adversely affect Aquatic Ecosystem

Dredging however may adversely affect Aquatic Ecosystem

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Variety of Dredging Operations

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Maintenance Dredging – removal of accumulated sediments from harbor channels and berths to

ensure a safe depth of water for navigational purposes

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Environmental Dredging – similar maintenance works to remove

sediments to restore an adequate flow of water to mitigate risk of

flooding or protect sensitive habitat

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Capital Dredging – excavation of materials to deepen or create

navigational channel and berths to provide additional harbor

infrastructure or to provide access for deeper draft vessels

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Construction Dredging – applies to removal of areas of the seabed during construction works at sea associated

with placement of other structures such as foundations, laying of

pipelines and outfalls

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Pre – Sweep Dredging – preparation of the sea bed to level

and remove obstruction preparatory to laying of pipelines

and cables

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Types of Dredging Equipment

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Clamshell or Grab Dredger – is a type of dredge of one or more

buckets operated by a crane and mounted on a floating vessel or

barge, usually located directly on the shore or positioned offshore

by anchor or moorings

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Clampshell or Grab DredgerClampshell or Grab Dredger

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“Clamshell” type bucket“Clamshell” type bucket

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Dipper Dredger or Backhoe Dredger – operate somewhat

similarly to a land based power shovel, characterize as an

excavator and that excavated materials are loaded on to barges

or on land

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Ladder Bucket Dredger – this type of dredger is configure with long steel frame which is easily lowered and

raised, equipped with multiple buckets passing over sprockets and scoop

materials from the bottom and discharge it through a chute into a

hopper moored alongside or receiving hopper located on the dredger

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Ladder Bucket DredgerLadder Bucket Dredger

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Cutter Suction Dredger – is a type of hydraulic dredger used for

loosening hard compact materials. The most common feature is the rotating cutter mounted on the

lower end of the ladder that support both the cutter drive and

suction pipe

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The cutterhead of a hydraulic dredgeThe cutterhead of a hydraulic dredge

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Hydraulic or Suction Dredger – used to excavate soft fine

materials such as sand and mud. It consist of a pipe joined at one end

to a centrifugal pump. Deep suction can excavate sand from

depth of 328 ft (100 m)

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Hydraulic dredging with a pipeline.Hydraulic dredging with a pipeline.

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Suction Dredge PipeSuction Dredge Pipe

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Suction Type DredgerSuction Type Dredger

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Mechanical dredging using a crane and bargeMechanical dredging using a crane and barge

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Trailing Suction Hopper Dredge – are self-propelled hydraulic

dredge with large drag arms and a high pumping capacity. This type

of dredge is primarily used in clearing channels and offshore

sand bars from the mouth of rivers

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Self-propelled hopper dredgeSelf-propelled hopper dredge

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Environmental Impact of Maintenance Dredging and

Disposal

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Factors Influencing the Potential Effects

• Magnitude and frequency of dredging activity• Methods of Dredging and Disposal• Channel size and depth• Size, density and quality of the material• Level of water, suspended sediment and turbidity• Tidal Range• Current, direction and velocity• Proximity of marine features to the dredging and

disposal activity• Presence and sensitivity of plant and animal

communities

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Generally, the Potential Impact of Dredging and Disposal can be

summarized as follows:

• Removal of subtidal Benthic species and communities

• Short term increases in the level of suspended sediments can give rise to changes in water quality which can effect marine life due to the increased turbidity and the possible release of organic matter, nutrients and contaminants depending on the nature of material in the area

• Settlement of these suspended sediments can result in the smothering or blanketing of subtidal communities although beneficially used to raise the level of selected areas to offset rise in sea level or erosion (short term impact vs long term gain

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