Misplaced Pages

#593406

32-729: Whangārei Harbour is a large harbour on the east coast of the North Island of New Zealand. The harbour stretches from Whangārei City , and the termination of the Hātea River , south east around the Onerahi peninsula and out to the Pacific Ocean at Whangārei Heads . Its Māori-language name (given by the Ngāti Wai iwi (tribe)) is Whangārei-te-rerenga-parāoa , meaning "the place where whales gather". Another traditional name for this area

64-434: A jetty or a mole , may be connected to land or freestanding, and may contain a walkway or road for vehicle access. Part of a coastal management system, breakwaters are installed parallel to the shore to minimize erosion . On beaches where longshore drift threatens the erosion of beach material, smaller structures on the beach may be installed, usually perpendicular to the water's edge. Their action on waves and current

96-399: A body of water is protected and deep enough to allow anchorage. Many such harbors are rias . Natural harbors have long been of great strategic naval and economic importance, and many great cities of the world are located on them. Having a protected harbor reduces or eliminates the need for breakwaters as it will result in calmer waves inside the harbor. Some examples are: For harbors near

128-415: A function of the distance the breakwaters are built from the coast, the direction at which the wave hits the breakwater, and the angle at which the breakwater is built (relative to the coast). Of these three, the angle at which the breakwater is built is most important in the engineered formation of salients. The angle at which the breakwater is built determines the new direction of the waves (after they've hit

160-442: A significant saving over revetment breakwaters. An additional rubble mound is sometimes placed in front of the vertical structure in order to absorb wave energy and thus reduce wave reflection and horizontal wave pressure on the vertical wall. Such a design provides additional protection on the sea side and a quay wall on the inner side of the breakwater, but it can enhance wave overtopping . A similar but more sophisticated concept

192-643: Is Long Beach Harbor , California , United States, which was an array of salt marshes and tidal flats too shallow for modern merchant ships before it was first dredged in the early 20th century. In contrast, a natural harbor is surrounded on several sides by land. Examples of natural harbors include Sydney Harbour , New South Wales, Australia, Halifax Harbour in Halifax, Nova Scotia , Canada and Trincomalee Harbour in Sri Lanka. Artificial harbors are frequently built for use as ports. The oldest artificial harbor known

224-479: Is Whangarei-o-te-tohorā – "waiting for the breastbone of whales". Many early settlers and Maori used the harbour as a form of transport, and this played a large role in the establishment of Whangārei , and many of the industries in the area. These include Portland Cement Works , Marsden Point Oil Refinery and for the extraction of coal from Kamo . From 1911–1933 the Onerahi Branch Railway crossed

256-651: Is a wave-absorbing caisson, including various types of perforation in the front wall. Such structures have been used successfully in the offshore oil-industry, but also on coastal projects requiring rather low-crested structures (e.g. on an urban promenade where the sea view is an important aspect, as seen in Beirut and Monaco ). In the latter, a project is presently ongoing at the Anse du Portier including 18 wave-absorbing 27 m (89 ft) high caissons. Wave attenuators consist of concrete elements placed horizontally one foot under

288-518: 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 structure (i.e. water on both sides). Rubble mound breakwaters use structural voids to dissipate the wave energy. Rubble mound breakwaters consist of piles of stones more or less sorted according to their unit weight: smaller stones for

320-465: Is intended to slow the longshore drift and discourage mobilisation of beach material. In this usage they are more usually referred to as groynes . Breakwaters reduce the intensity of wave action in inshore waters and thereby provide safe harbourage. Breakwaters may also be small structures designed to protect a gently sloping beach to reduce coastal erosion ; they are placed 100–300 feet (30–90 m) offshore in relatively shallow water. An anchorage

352-430: Is limited in practice by the natural fracture properties of locally available rock. Shaped concrete armour units (such as Dolos , Xbloc , Tetrapod , etc.) can be provided in up to approximately 40 tonnes (e.g. Jorf Lasfar , Morocco), before they become vulnerable to damage under self weight, wave impact and thermal cracking of the complex shapes during casting/curing. Where the very largest armour units are required for

SECTION 10

#1732851162594

384-809: Is only safe if ships anchored there are protected from the force of powerful waves by some large structure which they can shelter behind. Natural harbours are formed by such barriers as headlands or reefs . Artificial harbours can be created with the help of breakwaters. Mobile harbours, such as the D-Day Mulberry harbours , were floated into position and acted as breakwaters. Some natural harbours, such as those in Plymouth Sound , Portland Harbour , and Cherbourg , have been enhanced or extended by breakwaters made of rock. Types of breakwaters include vertical wall breakwater, mound breakwater and mound with superstructure or composite breakwater. A breakwater structure

416-483: Is popular with snorkelers due to the large amount of marine life seen there. Whangārei Harbour stretches approximately 23 km north-west from Whangārei Heads to its farthest point inland at the town basin in Whangārei central. At its widest point it is approximately 6 km wide, between Parua Bay and Takahiwai, near One Tree Point . The harbour is heavily tidal with a tidal range of approximately 2m, with much of

448-561: Is the Ancient Egyptian site at Wadi al-Jarf , on the Red Sea coast, which is at least 4500 years old (ca. 2600–2550 BCE, reign of King Khufu ). The largest artificially created harbor is Jebel Ali in Dubai . Other large and busy artificial harbors include: The Ancient Carthaginians constructed fortified, artificial harbors called cothons . A natural harbor is a landform where a section of

480-460: The North and South poles , being ice-free is an important advantage, especially when it is year-round. Examples of these are: The world's southernmost harbor, located at Antarctica 's Winter Quarters Bay (77° 50′ South), is sometimes ice-free, depending on the summertime pack ice conditions. Although the world's busiest port is a contested title, in 2017 the world's busiest harbor by cargo tonnage

512-466: The Newport breakwater. The dissipation of energy and relative calm water created in the lee of the breakwaters often encourage accretion of sediment (as per the design of the breakwater scheme). However, this can lead to excessive salient build up, resulting in tombolo formation, which reduces longshore drift shoreward of the breakwaters. This trapping of sediment can cause adverse effects down-drift of

544-520: The United States Army Corps of Engineers Coastal engineering manual (available for free online) and elsewhere. For detailed design the use of scaled physical hydraulic models remains the most reliable method for predicting real-life behavior of these complex structures. Breakwaters are subject to damage and overtopping in severe storms. Some may also have the effect of creating unique types of waves that attract surfers, such as The Wedge at

576-641: The breakwaters), and in turn the direction that sediment will flow and accumulate over time. The reduced heterogeneity in sea floor landscape introduced by breakwaters can lead to reduced species abundance and diversity in the surrounding ecosystems. As a result of the reduced heterogeneity and decreased depths that breakwaters produce due to sediment build up, the UV exposure and temperature in surrounding waters increase, which may disrupt surrounding ecosystems. There are two main types of offshore breakwater (also called detached breakwater): single and multiple. Single, as

608-403: The breakwaters, leading to beach sediment starvation and increased coastal erosion . This may then lead to further engineering protection being needed down-drift of the breakwater development. Sediment accumulation in the areas surrounding breakwaters can cause flat areas with reduced depths, which changes the topographic landscape of the seabed. Salient formations as a result of breakwaters are

640-461: The collided wave energy and prevent the generation of standing waves. As design wave heights get larger, rubble mound breakwaters require larger armour units to resist the wave forces. These armour units can be formed of concrete or natural rock. The largest standard grading for rock armour units given in CIRIA 683 "The Rock Manual" is 10–15 tonnes. Larger gradings may be available, but the ultimate size

672-461: The core and larger stones as an armour layer protecting the core from wave attack. 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,

SECTION 20

#1732851162594

704-525: The effect of the incident wave, creates waves in phase opposition to the incident wave downstream from the slabs. A submerged flexible mound breakwater can be employed for wave control in shallow water as an advanced alternative to the conventional rigid submerged designs. Further to the fact that, the construction cost of the submerged flexible mound breakwaters is less than that of the conventional submerged breakwaters, ships and marine organisms can pass them, if being deep enough. These marine structures reduce

736-538: The former ports at Whangārei and Onerahi to be located so far into the harbour. The main rivers flowing into the harbour are Hātea River, Mangapai River , Limeburners Creek, Raumanga Stream and Otaika Creek. They carry much sediment from surrounding farmland, creating the muddy nature of the harbour, and this requires dredging in some parts for navigation purposes. As the naming of the harbour indicates, southern right whales ( Tohora ) and possibly other coastal species like humpback and Bryde's whales used to gather in

768-406: The free surface, positioned along a line parallel to the coast. Wave attenuators have four slabs facing the sea, one vertical slab, and two slabs facing the land; each slab is separated from the next by a space of 200 millimetres (7.9 in). The row of four sea-facing and two land-facing slabs reflects offshore wave by the action of the volume of water located under it which, made to oscillate under

800-433: The harbour being shallower than this in the wider parts. This means during low tide much of the harbour is mud flats and exposed sand bars . However, at the harbour entrance, where it is only around 800m wide, and between Onerahi and Matakohe Island , where it is only around 500m wide, it is up to 20m deep and currents can be strong. This allowed for the deep water Northland Port to be built at Marsden Point and for

832-575: The harbour historically, but today it is not often to see baleen whales in the harbour due to their small population sizes and slow recoveries caused by commercial whaling by Europeans and Maoris (a whaling station was situated in the harbour), and illegal mass whaling operations by Soviet Union with supports by Japan (it is said that if these illegal operations had not taken place, the numbers of whales in New Zealand would have been three to four times larger than those of today). The first documented return of

864-450: The material requirements—and hence costs—increase significantly. 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

896-623: The most exposed locations in very deep water, armour units are most often formed of concrete cubes, which have been used up to ~ 195 tonnes Archived 2019-05-12 at the Wayback Machine for the tip of the breakwater at Punta Langosteira near La Coruña, Spain. Preliminary design of armour unit size is often undertaken using the Hudson's equation , Van der Meer and more recently Van Gent et al.; these methods are all described in CIRIA 683 "The Rock Manual" and

928-414: The name suggests, means the breakwater consists of one unbroken barrier, while multiple breakwaters (in numbers anywhere from two to twenty) are positioned with gaps in between (160–980 feet or 50–300 metres). The length of the gap is largely governed by the interacting wavelengths. Breakwaters may be either fixed or floating, and impermeable or permeable to allow sediment transfer shoreward of the structures,

960-460: The southern right whales into the harbour was in 2002. Smaller cetaceans such as dolphins and killer whales (orcas) can be observed in the harbour more frequently. Harbour Harbors may be natural or artificial. An artificial harbor can have deliberately constructed breakwaters , sea walls , or jetties or they can be constructed by dredging , which requires maintenance by further periodic dredging. An example of an artificial harbor

992-579: The upper reaches of the harbour to provide rail access to a new wharf built at Onerahi , as the existing wharf in the town basin was unreachable for some craft. This further promoted the harbour as an important feature to the development of Whangārei. In 2006, two marine reserves were opened in Whangārei Harbour. Whangarei Harbour Marine Reserve is located in an inter-tidal area between Onerahi and Waikaraka, and another around Motukaroro Island, at Reotahi, Whangārei Heads . The Motukaroro Island reserve

Whangārei Harbour - Misplaced Pages Continue

1024-477: Was the Port of Ningbo-Zhoushan . The following are large natural harbors: Breakwater (structure) A breakwater is a permanent structure constructed at a coastal area to protect against tides, currents, waves, and storm surges. Breakwaters have been built since antiquity to protect anchorages , helping isolate vessels from marine hazards such as wind-driven waves. A breakwater, also known in some contexts as

#593406