The swash zone is located at the landward edge of the surf zone on the upper part of the beach profile that is subjected to inundation (Fig. 8.1 A). It is where incoming surf zone waves force oscillatory motion of the shoreline (land–sea boundary) at a variety of frequencies, typically greater than 0.003 Hz.
Full Answer
Where is the swash zone?
The swash zone is located at the landward edge of the surf zone on the upper part of the beach profile that is subjected to inundation (Fig. 8.1A). It is where incoming surf zone waves force oscillatory motion of the shoreline (land–sea boundary) at a variety of frequencies, typically greater than 0.003 Hz.
What is swash zone in geography?
Definition of Swash zone: The zone where wave bores run up the beach. It extends from the limit of run-down to the limit of wave run-up.
What is the swash zone quizlet?
The swash zone is the nearest off-shore zone to the beach. Water moving parallel to the shore is called - Longshore drift. What is the difference between Eustatic and Relative sea level? Eustatic refers to the global sea level; Relative refers to local sea level near land.
What is swash in the ocean?
Swash is the name given to the waves that rush up the beach after a wave has broken. They are intriguing little waves that inhabit a world of their own. Most of the waves we see in the sea are known as 'waves of oscillation'. The water moves up and down in an orbital way, as energy moves from one place to another.
How is a swash measured?
Monitor the waves breaking on the shore for 10 minutes. Measure the time (in seconds) that the swash of each wave moves upwards. Note whether the backwash of each wave either drains into the beach material, runs back down the shore before the next wave arrives or interferes with the swash of the next wave.
Why do waves break?
Scientists have concluded that waves break when their amplitude reaches a critical level that causes large amounts of wave energy to be transformed into turbulent kinetic energy, like a ball rolling down the hill.
What is the most likely cause of beach erosion on wide beaches quizlet?
Coastal processes, such as beach drift, longshore drift, and local wave erosion, are the primary causes of coastal erosion.
What part of the littoral zone is covered by water during high tide but exposed during low tide quizlet?
Everywhere in Between: The littoral zone covers a large area of water, including the supralittoral zone, which is the area that always lies above the highest tide, and the sublittoral zone, which is the area that is always covered by water, even during low tide.
Where does beach sand primarily come from?
rocksMost beaches get their sand from rocks on land. Over time, rain, ice, wind, heat, cold, and even plants and animals break rock into smaller pieces. This weathering may begin with large boulders that break into smaller rocks. Water running through cracks erodes the rock.
What does a swash look like?
A swash is a typographical flourish, such as an exaggerated serif, terminal, tail, entry stroke, etc., on a glyph. The use of swash characters dates back to at least the 16th century, as they can be seen in Ludovico Vicentino degli Arrighi's La Operina, which is dated 1522.
Why does water go back in the beach?
On a sandy beach with a gently sloping shore, the swell simply pushes uphill. The climb up the beach drains all the energy of the surge, and the water eventually flows downhill, back to the ocean -- in other words, the water finds its own level again. Ordinarily, this receding flow of water moves with minimal force.
Whats it called when a wave goes back into the ocean?
Backwash waves are nothing but counter or reverse waves that move toward the ocean instead of traveling toward the coast. A backwash wave may be dangerous to beachgoers who are not comfortable in high surf or turbulent seas but are also a rare and unusual wave riding opportunity for surfers.
What is Tombolo in geography?
tombolo, one or more sandbars or spits that connect an island to the mainland. A single tombolo may connect a tied island to the mainland, as at Marblehead, Mass. A double tombolo encloses a lagoon that eventually fills with sediment; fine examples of these occur off the coast of Italy.
What is a fetch in geography?
fetch, area of ocean or lake surface over which the wind blows in an essentially constant direction, thus generating waves. The term also is used as a synonym for fetch length, which is the horizontal distance over which wave-generating winds blow.
What is longshore drift in geography?
Waves that hit the beach at an angle carry sand and gravel up the beach face at an angle. When the water washes back the sediment. is carried straight back down the beach face. Individual particles are moved along the beach in a zig zag pattern. This is called longshore drift.
What is deposition in geography?
Deposition is the laying down of sediment carried by wind, flowing water, the sea or ice. Sediment can be transported as pebbles, sand and mud, or as salts dissolved in water.
What is the swash zone?
The swash zone is alternately wet and dry. Infiltration (hydrology) (above the water table) and exfiltration (below the water table) take place between the swash flow and the beach groundwater table. Beachface, berm, beach step and beach cusps are the typical morphological features associated with swash motion.
Where does swash occur?
Greater swash generally occurs on flatter beaches. The swash motion plays the primary role in the formation of morphological features and their changes in the swash zone. The swash action also plays an important role as one of the instantaneous processes in wider coastal morphodynamics. Figure 1.
What is the role of swash motion in beach erosion?
The transport rates in the swash zone are much higher compared to the surf zone and suspended sediment concentrations can exceed 100 kg/m 3 close to the bed. The onshore and offshore sediment transport by swash thus plays a significant role in accretion and erosion of the beach.
What is a berm in swash?
The berm is the relatively planar part of the swash zone where the accumulation of sediment occurs at the landward farthest of swash motion (Figure 2). The berm protects the backbeach and coastal dunes from waves but erosion can occur under high energy conditions such as storms. The berm is more easily defined on gravel beaches and there can be multiple berms at different elevations. On sandy beaches in contrast, the gradient of backbeach, berm and beachface can be similar. The height of the berm is governed by the maximum elevation of sediment transport during the uprush. The berm height can be predicted using the equation by Takeda and Sunamura (1982)
How does sediment transport differ between swash and uprush?
There are fundamental differences in sediment transport between the uprush and backwash of the swash flow. The uprush, which is mainly dominated by bore turbulence, especially on steep beaches, generally suspend sediments to transport. Flow velocities, suspended sediment concentrations and suspended fluxes are at greatest at the start of the uprush when the turbulence is maximum. Then the turbulence dissipates towards the end of the onshore flow, settling the suspended sediment to the bed. In contrast, the backwash is dominated by the sheet flow and bedload sediment transport. The flow velocity increases towards the end of the backwash causing more bed-generated turbulence, which results in sediment transport near the bed. The direction of the net sediment transport (onshore or offshore) is largely governed by the beachface gradient.
What are the phases of swash?
Swash consists of two phases: uprush (onshore flow) and backwash (offshore flow). Generally, uprush has higher velocity and shorter duration than backwash. Onshore velocities are at greatest at the start of the uprush and then decrease, whereas offshore velocities increase towards the end of the backwash.
Why is understanding the sediment transport system in the swash zone important?
Understanding the sediment transport system in the swash zone is also vital for beach nourishment projects. Swash plays a significant role in transportation and distribution of the sand that is added to the beach. There have been failures in the past due to inadequate understanding. Understanding and prediction of the sediment movements, both in the swash and surf zone, is vital for the nourishment project to succeed.
What is the swash zone?
The swash zone forms the land-ocean boundary at the landward edge of the surf zone, where waves runup the beach face (figures 1, 2). It is perhaps the region of the ocean most actively used by recreational beach users and, being very visible, is the region of the littoral zone most associated with beach erosion and the impacts of climate change. The landward edge of the swash zone is highly variable in terms of geomorphology, and may terminate in dunes, cliffs, marshes, ephemeral estuaries and a wide variety of sand, gravel, rock or coral barriers. This influences the exchange of sediment between the land and ocean, which ultimately forms the coastline.
What are the characteristics of a swash zone?
The characteristics of the swash zone hydrodynamics and sediment transport are governed by the inner surf zone and the underlying beach, with feedback of course between the morphology and hydrodynamic processes. The beach slope is a controlling parameter . On dissipative beaches, with wide surf zones, most of the wind wave and swell energy is dissipated seaward of the swash zone. Therefore, swash processes are dominated by those due to long, or infragravity waves, which are frequently non-breaking standing waves (figure 2a). On intermediate and reflective beaches, short wave energy reaches the beach face in the form of bores or shore-breaks, which collapse at the beach, initiating a runup motion characterised by a thin sheet of water with a rapidly propagating wave tip which is analogous to a dam-break flow over a dry bed (figure 2b). This sheet of water is slowed by gravity and friction until the flow reverses and forms another shallow flow seaward, the backwash. On coarse grained sand and gravel beaches a significant volume of the uprush and some of the backwash may percolate into the beach, reducing the volume of water in the surface backwash flow. These two distinct types of swash zone make modelling hydrodynamic processes difficult, since parametric models rely on similarity of processes, and therefore phase resolving models of the whole surf zone, or at least the inner surf zone, are required if the details of the hydrodynamics are required. Fortunately some processes are modelled very well by parametric models, perhaps more accurately than phase-resolving models, particularly wave runup.
How fast is a backwash?
Runup and backwash velocities in the field reach 2-5 m/s, which are generally larger than those in the surf zone. The runup durations are typically shorter than the backwash duration, and the backwash depths are shallower than during the uprush, and therefore the velocity moments tend to be skewed offshore, which has important implications for the sediment dynamics . The asymmetry is however affected by the mass and momentum advected into the swash zone, which depends on the flow in the inner surf zone. Self-similar solutions for different boundary conditions are presented by Guard and Baldock , following the work of Peregrine and Williams , figure 6. These indicate the fundamental nature of the hydrodynamics, which comprise of a near parabolic motion of the shoreline (due to gravity being the dominant process) and a saw-tooth shaped variation in velocity with time, which decreases at a near linear rate from the peak velocity, which occurs as the shoreline passes a given location. The water surface slope dips seaward for nearly the whole swash cycle, i.e. the total fluid acceleration is offshore throughout the swash cycle.
How does swash-swash interaction occur?
Swash-swash interactions occur through the overtaking of a swash uprush by the following bore or during the collision of the backwash flow with the next uprush . The magnitude, or vertical excursion, of the swash oscillations, from rundown position to runup, is strongly influenced by interaction between wave uprush and backwash, with the period of the incident waves also controlling the period of the swash oscillations at swell and wind wave frequencies . Hence, given a finite time for the uprush and backwash to occur, there is a finite magnitude for a swash oscillation at a given frequency on a given beach slope if the motion is solely controlled by gravity. This leads to swash saturation, where an increase in incident wave height does not increase the magnitude of the swash oscillations. This can be parameterised for individual events, or through a spectral representation.
How much of the longshore sediment transport is in the swash zone?
While the relative importance of longshore transport in the swash zone compared to the surf zone is greater during milder wave conditions than during storms, longshore sediment transport in the swash zone may account for up to 50% of the total longshore transport .
What is the role of swash in coastal erosion?
In terms of coastal processes and coastal protection, a large part of the littoral sediment transport occurs in the swash zone, both cross-shore and longshore, which influences beach morphology , and beach erosion and beach recovery during and after storms. Wave runup is an important factor in the design of coastal protection and also generates hazards for beach users, and is the dominant process leading to the erosion of coastal dunes. Swash hydrodynamics also influence the ecology of the intertidal zone and groundwater levels in sub-aerial littoral beaches and low lying islands, which is often critical for freshwater water supply on islands and atolls .
How does sediment transport occur in the swash zone?
Cross-shore sediment transport in the swash zone generally occurs as a combination of bed load under sheet flow conditions, with a flat bed, plus an additional component of suspended load, generated locally and advected into the swash zone by surf zone bores. For the bed load, the Meyer-Peter and Muller formulation, or derivatives, generally perform well with calibration, i.e. determining the transport coefficient and friction factor remain problematic. In these models, the transport is typically a function of the velocity cubed (see for a more detailed discussion the article Sand transport ). The relative balance between bed load, which is generated locally, and suspended load depends on the sediment grain size, and also on the quantity of sediment advected into the swash zone from the inner surf zone (figure 8). This can be considerable, and affects the distribution of suspended load across the swash zone. While the basic sediment transport equations still apply, model-data comparisons are lacking, particularly close to the bed where suspended sediment concentrations are largest.
