Misplaced Pages

#230769

52-697: Tuggerah Lake , an intermittently open intermediate wave dominated barrier estuary that is part of the Tuggerah Lakes , is located within the Central Coast Council local government area in the Central Coast region of New South Wales , Australia. The lake is located near Wyong and is situated about 90 kilometres (56 mi) north of Sydney . Drawing its catchment from the Wyong River , Ourimbah Creek and Tumbi Creek, at

104-399: A deep-water wave may also be approximated by: where g is the acceleration due to gravity, 9.8 meters (32 feet) per second squared. Because g and π (3.14) are constants, the equation can be reduced to: when C is measured in meters per second and L in meters. In both formulas the wave speed is proportional to the square root of the wavelength. The speed of shallow-water waves is described by

156-456: A different equation that may be written as: where C is speed (in meters per second), g is the acceleration due to gravity, and d is the depth of the water (in meters). The period of a wave remains unchanged regardless of the depth of water through which it is moving. As deep-water waves enter the shallows and feel the bottom, however, their speed is reduced, and their crests "bunch up", so their wavelength shortens. Sea state can be described by

208-420: A period of time is usually expressed as significant wave height . This figure represents an average height of the highest one-third of the waves in a given time period (usually chosen somewhere in the range from 20 minutes to twelve hours), or in a specific wave or storm system. The significant wave height is also the value a "trained observer" (e.g. from a ship's crew) would estimate from visual observation of

260-413: A sea state. Given the variability of wave height, the largest individual waves are likely to be somewhat less than twice the reported significant wave height for a particular day or storm. Wave formation on an initially flat water surface by wind is started by a random distribution of normal pressure of turbulent wind flow over the water. This pressure fluctuation produces normal and tangential stresses in

312-469: A surface area of 81 square kilometres (31 sq mi). When full, Tuggerah Lake covers an area of around 5,400 hectares (13,000 acres). Heavy rains in June 2007 caused Tuggerah Lake to flood, affecting areas of Long Jetty , Killarney Vale and Chittaway Point . On the sea side of the peninsula is Norah Head and its historic lighthouse . The lake adjoins extensive areas of suburban development. Much of

364-443: Is surface tension . Sea waves are larger-scale, often irregular motions that form under sustained winds. These waves tend to last much longer, even after the wind has died, and the restoring force that allows them to propagate is gravity. As waves propagate away from their area of origin, they naturally separate into groups of common direction and wavelength. The sets of waves formed in this manner are known as swells. The Pacific Ocean

416-535: Is 19,800 km (12,300 mi) from Indonesia to the coast of Colombia and, based on an average wavelength of 76.5 m (251 ft), would have ~258,824 swells over that width. It is sometimes alleged that out of a set of waves, the seventh wave in a set is always the largest; while this isn't the case, the waves in the middle of a given set tend to be larger than those before and after them. Individual " rogue waves " (also called "freak waves", "monster waves", "killer waves", and "king waves") much higher than

468-406: Is Long Jetty, so named for the jetty built to service the first sub-division of land at The Entrance. The original jetty was washed away in a flood at Easter 1927; the present structure replaced it, built in 1927–28 to a length of 1,152 feet (351 m). Parts of the jetty have fallen into disrepair and it requires frequent periodic repairs and replacement of its structure and decking. Tuggerah Lake

520-571: Is available across the entire lake. Substantial residential and commercial development, involving excavation and alteration of native vegetation and natural watercourses in the lake catchment and hinterland, has given rise to siltation and changes in the make up of the lakebed and foreshore. During 2004 and 2005 the Tuggerah Lakes Restoration project has been attempting to restore and revive the lake system. Urbanisation and development have caused increased nutrients to build up in

572-406: Is called shoaling . Wave refraction is the process that occurs when waves interact with the sea bed to slow the velocity of propagation as a function of wavelength and period. As the waves slow down in shoaling water, the crests tend to realign at a decreasing angle to the depth contours. Varying depths along a wave crest cause the crest to travel at different phase speeds , with those parts of

SECTION 10

#1732783881231

624-495: Is concentrated as they converge, with a resulting increase in wave height. Because these effects are related to a spatial variation in the phase speed, and because the phase speed also changes with the ambient current—due to the Doppler shift —the same effects of refraction and altering wave height also occur due to current variations. In the case of meeting an adverse current the wave steepens , i.e. its wave height increases while

676-438: Is inevitable. Individual waves in deep water break when the wave steepness—the ratio of the wave height H to the wavelength λ —exceeds about 0.17, so for H  > 0.17  λ . In shallow water, with the water depth small compared to the wavelength, the individual waves break when their wave height H is larger than 0.8 times the water depth h , that is H  > 0.8  h . Waves can also break if

728-503: Is measured in metres. This expression tells us that waves of different wavelengths travel at different speeds. The fastest waves in a storm are the ones with the longest wavelength. As a result, after a storm, the first waves to arrive on the coast are the long-wavelength swells. For intermediate and shallow water, the Boussinesq equations are applicable, combining frequency dispersion and nonlinear effects. And in very shallow water,

780-435: Is proportional to the curvature of the velocity profile of the wind at the point where the mean wind speed is equal to the wave speed. Since the wind speed profile is logarithmic to the water surface, the curvature has a negative sign at this point. This relation shows the wind flow transferring its kinetic energy to the water surface at their interface. Assumptions: Generally, these wave formation mechanisms occur together on

832-627: Is the wave elevation, ϵ j {\displaystyle \epsilon _{j}} is uniformly distributed between 0 and 2 π {\displaystyle 2\pi } , and Θ j {\displaystyle \Theta _{j}} is randomly drawn from the directional distribution function f ( Θ ) : {\displaystyle {\sqrt {f(\Theta )}}:} As waves travel from deep to shallow water, their shape changes (wave height increases, speed decreases, and length decreases as wave orbits become asymmetrical). This process

884-572: Is well known for its recreational fishing with species such as luderick , bream , flathead and whiting caught from the shoreline and boats. Prawns can be plentiful over the summer months during the dark of the new moon. Fishing in Tuggerah Lake is generally poor during late winter and early spring, particularly when westerly winds are prevalent. Special purpose markers (coloured yellow) around Terilbah Island and Pelican Island denote areas where net and trap fishing are restricted. Other parts of

936-507: The RRS Discovery in a sea with 18.5 m (61 ft) significant wave height, so the highest wave was only 1.6 times the significant wave height. The biggest recorded by a buoy (as of 2011) was 32.3 m (106 ft) high during the 2007 typhoon Krosa near Taiwan. Ocean waves can be classified based on: the disturbing force that creates them; the extent to which the disturbing force continues to influence them after formation;

988-430: The sea wave spectrum or just wave spectrum S ( ω , Θ ) {\displaystyle S(\omega ,\Theta )} . It is composed of a wave height spectrum (WHS) S ( ω ) {\displaystyle S(\omega )} and a wave direction spectrum (WDS) f ( Θ ) {\displaystyle f(\Theta )} . Many interesting properties about

1040-471: The shallow water equations can be used. If the wavelength is very long compared to the water depth, the phase speed (by taking the limit of c when the wavelength approaches infinity) can be approximated by Wyrrabalong National Park The Wyrrabalong National Park is a coastal national park that is located on the Central Coast of New South Wales , in eastern Australia . The 620-hectare (1,500-acre) national park consists of two sections;

1092-557: The Central Coast. Most of the park lies in the Tuggerah Important Bird Area , identified as such by BirdLife International because of its importance for a variety of water and woodland birds. The average elevation of the terrain is 8 metres. The land now occupied by Wyrrabalong National Park was first inhabited by the indigenous Darkinjung and Awabakal peoples. The Darkinjung occupied

SECTION 20

#1732783881231

1144-417: The Central Coast. The lake is part of the Tuggerah Important Bird Area , identified as such by BirdLife International because of its importance for a variety of water and woodland birds. Wind wave When directly generated and affected by local wind, a wind wave system is called a wind sea . Wind waves will travel in a great circle route after being generated – curving slightly left in

1196-471: The crest falling forward and down as it extends over the air ahead of the wave. Three main types of breaking waves are identified by surfers or surf lifesavers . Their varying characteristics make them more or less suitable for surfing and present different dangers. When the shoreline is near vertical, waves do not break but are reflected. Most of the energy is retained in the wave as it returns to seaward. Interference patterns are caused by superposition of

1248-464: The equilibrium of the water surface and transfer energy from the air to the water, forming waves. The initial formation of waves by the wind is described in the theory of Phillips from 1957, and the subsequent growth of the small waves has been modeled by Miles , also in 1957. In linear plane waves of one wavelength in deep water, parcels near the surface move not plainly up and down but in circular orbits: forward above and backward below (compared to

1300-475: The extent to which the restoring force weakens or flattens them; and their wavelength or period. Seismic sea waves have a period of about 20 minutes, and speeds of 760 km/h (470 mph). Wind waves (deep-water waves) have a period up to about 20 seconds. The speed of all ocean waves is controlled by gravity, wavelength, and water depth. Most characteristics of ocean waves depend on the relationship between their wavelength and water depth. Wavelength determines

1352-424: The faster the wave energy will move through the water. The relationship between the wavelength, period and velocity of any wave is: where C is speed (celerity), L is the wavelength, and T is the period (in seconds). Thus the speed of the wave derives from the functional dependence L ( T ) {\displaystyle L(T)} of the wavelength on the period (the dispersion relation ). The speed of

1404-460: The hyperbolic tangent approaches 1 {\displaystyle 1} , the speed c {\displaystyle c} approximates In SI units, with c deep {\displaystyle c_{\text{deep}}} in m/s, c deep ≈ 1.25 λ {\displaystyle c_{\text{deep}}\approx 1.25{\sqrt {\lambda }}} , when λ {\displaystyle \lambda }

1456-434: The incident and reflected waves, and the superposition may cause localized instability when peaks cross, and these peaks may break due to instability. (see also clapotic waves ) Wind waves are mechanical waves that propagate along the interface between water and air ; the restoring force is provided by gravity, and so they are often referred to as surface gravity waves . As the wind blows, pressure and friction perturb

1508-456: The interdependence between flow quantities such as the water surface movements, flow velocities , and water pressure . The key statistics of wind waves (both seas and swells) in evolving sea states can be predicted with wind wave models . Although waves are usually considered in the water seas of Earth, the hydrocarbon seas of Titan may also have wind-driven waves. Waves in bodies of water may also be generated by other causes, both at

1560-541: The lake may have permanent or temporary fishing restrictions in force. Due to its large size and shallow depth strong winds can whip up a steep choppy surface that can be hazardous to small boats, however Tuggerah Lake is considered quite safe for most forms of small recreational watercraft if common sense and general safe boating practices are followed. Many parts of Tuggerah Lake are quite shallow with sand or weed flats exposed at low water. Marked channels should be navigated with care and at reduced speed. Mobile phone coverage

1612-414: The lake stimulating weed growth. Restoration work has focussed on inshore removal of weed and ooze; foreshore reclamation and reinstatement; pollutant traps; and channel dredging to increase the tidal exchange of water with the sea. Wyrrabalong National Park borders the lake and the sea separating the residential areas of Toukley and The Entrance, and preserves the last significant littoral rainforest on

Tuggerah Lake - Misplaced Pages Continue

1664-406: The maximum wave size theoretically possible for a wind of specific strength, duration, and fetch. Further exposure to that specific wind could only cause a dissipation of energy due to the breaking of wave tops and formation of "whitecaps". Waves in a given area typically have a range of heights. For weather reporting and for scientific analysis of wind wave statistics, their characteristic height over

1716-507: The northern section consists of approximately 480 hectares (1,200 acres) and covers a substantial area of the peninsula between The Entrance and Norah Head as well as Terilbah and Pelican Islands within Tuggerah Lake . The southern section consists of about 120 hectares (300 acres) of the coast, from Shelly Beach south to Forresters Beach . The park is also noted for containing the last significant coastal (littoral) rainforest on

1768-432: The ocean are also called ocean surface waves and are mainly gravity waves , where gravity is the main equilibrium force. Wind waves have a certain amount of randomness : subsequent waves differ in height, duration, and shape with limited predictability. They can be described as a stochastic process , in combination with the physics governing their generation, growth, propagation, and decay – as well as governing

1820-482: The original settlement bordering the lake was oriented towards domestic tourism; with Sydney residents drawn to the area and staying in camp and early cabin-style accommodation clustered around towns of The Entrance and Long Jetty, from there spreading to Toukley on the northern lakeshore. Many towns surround the lake including Lake Munmorah , The Entrance , Killarney Vale , Berkeley Vale , Tumbi Umbi , Wyong , Kanwal , Gorokan and Toukley . South of The Entrance

1872-411: The other hand, the orbits of water molecules in waves moving through shallow water are flattened by the proximity of the sea bottom surface. Waves in water shallower than 1/20 their original wavelength are known as shallow-water waves. Transitional waves travel through water deeper than 1/20 their original wavelength but shallower than half their original wavelength. In general, the longer the wavelength,

1924-726: The other waves in the sea state can occur. In the case of the Draupner wave , its 25 m (82 ft) height was 2.2 times the significant wave height . Such waves are distinct from tides , caused by the Moon and Sun 's gravitational pull , tsunamis that are caused by underwater earthquakes or landslides , and waves generated by underwater explosions or the fall of meteorites —all having far longer wavelengths than wind waves. The largest ever recorded wind waves are not rogue waves, but standard waves in extreme sea states. For example, 29.1 m (95 ft) high waves were recorded on

1976-508: The sea state can be found from the wave spectra. WHS describes the spectral density of wave height variance ("power") versus wave frequency , with dimension { S ( ω ) } = { length 2 ⋅ time } {\displaystyle \{S(\omega )\}=\{{\text{length}}^{2}\cdot {\text{time}}\}} . The relationship between the spectrum S ( ω j ) {\displaystyle S(\omega _{j})} and

2028-483: The size of the orbits of water molecules within a wave, but water depth determines the shape of the orbits. The paths of water molecules in a wind wave are circular only when the wave is traveling in deep water. A wave cannot "feel" the bottom when it moves through water deeper than half its wavelength because too little wave energy is contained in the water movement below that depth. Waves moving through water deeper than half their wavelength are known as deep-water waves. On

2080-479: The southern half of Tuggerah Lake, the lake is generally quite shallow with an average depth of 2.4 metres (7 ft 10 in). It is connected with the Tasman Sea through a tidal channel at its southern end known as The Entrance . It is also connected with two smaller lakes, Budgewoi Lake and through that to Lake Munmorah. Tuggerah Lake has a catchment area of 714 square kilometres (276 sq mi) and

2132-484: The southern hemisphere and slightly right in the northern hemisphere. After moving out of the area of fetch and no longer being affected by the local wind, wind waves are called swells and can travel thousands of kilometers. A noteworthy example of this is waves generated south of Tasmania during heavy winds that will travel across the Pacific to southern California, producing desirable surfing conditions. Wind waves in

Tuggerah Lake - Misplaced Pages Continue

2184-724: The southern section and The Awabakal occupied the northern section. It is believed Europeans first discovered the Tuggerah Lakes in 1796. It was found by Governor of Tasmania , Colonel David Collins , who had arrived on the First Fleet , during the search for an escaped convict , Mary Morgan, who was said to be living with the Aborigines to the North of the Hawkesbury River . The average summer temperature

2236-505: The surface and underwater (such as watercraft , animals , waterfalls , landslides , earthquakes , bubbles , and impact events ). The great majority of large breakers seen at a beach result from distant winds. Five factors influence the formation of the flow structures in wind waves: All of these factors work together to determine the size of the water waves and the structure of the flow within them. The main dimensions associated with wave propagation are: A fully developed sea has

2288-413: The surface water, which generates waves. It is usually assumed for the purpose of theoretical analysis that: The second mechanism involves wind shear forces on the water surface. John W. Miles suggested a surface wave generation mechanism that is initiated by turbulent wind shear flows based on the inviscid Orr–Sommerfeld equation in 1957. He found the energy transfer from the wind to the water surface

2340-471: The surface. The phase speed (also called the celerity) of a surface gravity wave is—for pure periodic wave motion of small- amplitude waves—well approximated by where In deep water, where d ≥ 1 2 λ {\displaystyle d\geq {\frac {1}{2}}\lambda } , so 2 π d λ ≥ π {\displaystyle {\frac {2\pi d}{\lambda }}\geq \pi } and

2392-453: The water surface and eventually produce fully developed waves. For example, if we assume a flat sea surface (Beaufort state 0), and a sudden wind flow blows steadily across the sea surface, the physical wave generation process follows the sequence: Three different types of wind waves develop over time: Ripples appear on smooth water when the wind blows, but will die quickly if the wind stops. The restoring force that allows them to propagate

2444-456: The wave amplitude A j {\displaystyle A_{j}} for a wave component j {\displaystyle j} is: Some WHS models are listed below. As for WDS, an example model of f ( Θ ) {\displaystyle f(\Theta )} might be: Thus the sea state is fully determined and can be recreated by the following function where ζ {\displaystyle \zeta }

2496-423: The wave amplitude (height), the particle paths do not form closed orbits; rather, after the passage of each crest, particles are displaced slightly from their previous positions, a phenomenon known as Stokes drift . As the depth below the free surface increases, the radius of the circular motion decreases. At a depth equal to half the wavelength λ, the orbital movement has decayed to less than 5% of its value at

2548-409: The wave in deeper water moving faster than those in shallow water . This process continues while the depth decreases, and reverses if it increases again, but the wave leaving the shoal area may have changed direction considerably. Rays —lines normal to wave crests between which a fixed amount of energy flux is contained—converge on local shallows and shoals. Therefore, the wave energy between rays

2600-464: The wave propagation direction). As a result, the surface of the water forms not an exact sine wave , but more a trochoid with the sharper curves upwards—as modeled in trochoidal wave theory. Wind waves are thus a combination of transversal and longitudinal waves. When waves propagate in shallow water , (where the depth is less than half the wavelength) the particle trajectories are compressed into ellipses . In reality, for finite values of

2652-400: The wavelength decreases, similar to the shoaling when the water depth decreases. Some waves undergo a phenomenon called "breaking". A breaking wave is one whose base can no longer support its top, causing it to collapse. A wave breaks when it runs into shallow water , or when two wave systems oppose and combine forces. When the slope, or steepness ratio, of a wave, is too great, breaking

SECTION 50

#1732783881231

2704-404: The wind grows strong enough to blow the crest off the base of the wave. In shallow water, the base of the wave is decelerated by drag on the seabed. As a result, the upper parts will propagate at a higher velocity than the base and the leading face of the crest will become steeper and the trailing face flatter. This may be exaggerated to the extent that the leading face forms a barrel profile, with

#230769