- Harbor also spelled:
- harbour
- Key People:
- Thomas Telford
- John Rennie
Harbors and sea works
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What is a harbour?
A harbour is a protected part of a body of water that offers safe anchorage for ships. Natural harbours, such as New York Bay, are naturally-occurring inlets, bays, or estuaries. These harbours may need dredging and port structures but are fundamentally natural formations.
Because natural harbors aren't always available, engineers build artificial harbors using structures like breakwaters, jetties, or moles to create calm waters. Fishing harbours provide safety for boats and facilitate the swift transfer of fish to markets, also speeding up vessel maintenance and departure. These harbors need specific facilities like unloading, sorting, and weighing stations, market halls, ice plants, and processing plants.
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Why are harbours important for cities and countries?
Harbors are crucial for cities and countries because they provide safety for boats and facilitate the efficient transfer of goods and people. Natural harbors, like New York Bay, can become the foundation for great cities with some improvements and port structures. Where nature doesn't provide, engineers build artificial harbors using breakwaters to create calm waters. These harbors require facilities for unloading, sorting, and storage, as well as vessel repair and fuel. Good transportation links, like road and rail access, and effective communication networks are also vital.
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What kinds of structures are included in sea works?
Harbors and sea works include various man-made structures designed to protect vessels from harsh marine conditions, facilitate safe anchorage, and enable the efficient transfer of cargo and passengers.
Common structures include quay walls, which are retaining walls along the shore that protect the shore and serve as staging areas. Wharves, consisting of trestle-mounted platforms parallel to the shoreline, and piers, platforms extending over the water, provide additional berthing space. Breakwaters, which can be solid, vertical, or floating, are substantial structures designed to absorb or deflect wave energy. Also, docks are artificially enclosed basins used for vessel inspection and repair. Lighthouses guide mariners by offering visual and radio signals, and seawalls protect the shore from erosion.
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How do breakwaters help protect harbours?
Breakwaters protect harbors by reducing the force of waves. They are substantial offshore structures designed to either absorb or deflect the energy of incoming waves, creating a sheltered basin for harbors, anchorages, and marinas.
There are different breakwater designs, including floating, solid, and rubble mound breakwaters. Rubble mound breakwaters consist of an inner mound of small rocks for stability, covered by an outer layer of larger boulders or concrete shapes for protection against wave action. Floating breakwaters use massive moorings to remain in place, while solid breakwaters of concrete or masonry rely on vertical reflection to repel waves. Breakwaters also help prevent beach erosion by intercepting longshore currents.
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What challenges do engineers face when building harbours?
Building harbours and sea works presents unique civil engineering challenges because the sea constantly tests the structures designed to resist it. Some challenges include:
* Land support Civil engineers must discover how to support land next to water that is deep enough to float large ships. The economic challenge posed by the increase in the size of modern ships is considerable.
* Dredging Many navigable harbors require the removal of unwanted material because the continuing accumulation can obstruct navigation. The current trend toward larger ships makes dredging especially important.
* Soil conditions Accidents caused by soil instability still occasionally occur. In modern practice, projects are not initiated without exhaustive exploration of the soil conditions by means of borings and laboratory tests on the samples. Continuous monitoring of the soil conditions during construction is also considered essential.
* Economic factors The capital cost of harbor construction increases in proportion to the deepest draft of ship capable of being accommodated.
* Adverse weather Harbours must be able to withstand the impact of storms and other extreme weather events, which can cause structural damage, erosion, and flooding.1 Britannica SourceCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How do harbours and sea works affect the environment?
Harbors and sea works significantly impact the environment. Construction and maintenance require dredging, which involves removing silt and other materials from the seabed. Dredging can disturb aquatic habitats and increase water turbidity, affecting marine life.
Breakwaters, while protecting harbors from waves and erosion, can disrupt longshore currents, leading to sediment deposition in some areas and erosion in others. Noise pollution from ships and construction activities can also harm marine animals, interfering with their communication, navigation, and ability to find food or avoid predators. Additionally, the physical structures of harbors can lead to habitat loss and alteration.
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Harbors and sea works, any part of a body of water and the constructions surrounding it that sufficiently shelters a vessel from wind, waves, and currents, enabling safe anchorage or the discharge and loading of cargo and passengers. The construction of harbors and sea works offers some of the most unusual problems and challenges in civil engineering. The continuous and immediate presence of the sea provides the engineer with an adversary certain to discover any weakness in the structure built to resist it.
Principles of maritime engineering
Objectives
The principal objectives of such works fall broadly into two classifications: improvement of transportation, and reclamation and conservancy of land. Under the first fall works directed at providing facilities for the safe and economical transfer of cargo and passengers between land vehicles and ships; fishing ports for the landing and distribution of the harvest of the sea; harbors of refuge for ships and small craft; and marinas for the mooring or laying up of small private craft. Under the heading of reclamation and conservancy come works directed to the protection of the land area from encroachment by the sea, to the recovery and conversion to land use of areas occupied by the sea, and to the maintenance of river estuaries as efficient means for the discharge of inland runoff. In many places, without continuous attention to such maintenance, the coincidence of high tides with heavy rainfall would lead to frequent disastrous flooding of inhabited areas.
The civil engineering techniques used for either of these objectives are broadly similar, and indeed the realization of both objectives at the same time will frequently be a feature of the same project. An operation of maintaining a river estuary at a depth sufficient for navigation, for example, may at the same time greatly improve its capacity for the drainage of upland floodwaters.
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Hydraulic models
The planning of maritime civil engineering works, whether for transportation, reclamation, or conservancy, has been facilitated by the development of the technique of model studies. Once regarded as scientific toys, such studies are now considered an essential preliminary step to any large-scale redevelopment of a port or coastal area and are useful even for minor modifications or additions.
Scale models of the area, harbor, or estuary are made so that water can be caused to flow in such a way as to reproduce the various tidal and other streams in the same direction and with velocities equivalent to those occurring on the site. A variety of devices, usually electronically controlled, have been developed to produce both wave and tidal effects.
The value of these experiments derives from the reduction in the time scale, which has been found to correspond to the reduction in the dimensional scales of the model. Thus, the large model of the Clyde estuary of Scotland works on a tidal cycle of about 14 minutes, or about 50 times the actual frequency. The effect of three years of tides following any modification of the profile of the harbor can thus be studied on the model in a matter of three weeks, and any tendency to otherwise unanticipated scour (clearing by powerful current) or siltation can probably be detected. The relative values of alternative positions of breakwaters in affording shelter can be similarly studied using the wave-generating devices available; and the development of secondary, or reflected, waves with undesirable disturbances within the sheltered area may be anticipated and, if possible, forestalled.
Natural and artificial harbors
In certain favored points on the world’s coastlines, nature has provided harbors waiting only to be used, such as New York Bay, which the explorer Giovanni da Verrazzano described as “a very agreeable location” for sheltering a ship. Such inlets, bays, and estuaries may require improvement by dredging and must be supplied with port structures, but basically they remain as nature made them, and their existence accounts for many of the world’s great cities. Because such natural harbors are not always at hand where port facilities are needed, engineers must create artificial harbors. The basic structure involved in the creation of an artificial harbor is a breakwater, sometimes called a jetty, or mole, the function of which is to provide calm water inshore. Locations for artificial harbors are of course chosen with an eye to the existing potential of the coast; an indentation, however slight, is favored. Yet it has often been found justifiable on economic or strategic grounds to construct a complete harbor on a relatively unsheltered coastline by enclosing an area with breakwaters built from the shore, with openings of minimum width for entry and exit of ships.
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