A beach is a depositional feature found along coastlines. They can be composed of sand, gravel or larger cobbles or boulders.
2. Explain how the size of beach sediment can affect the shape or profile of a beach. (4)
The beach profile describes its shape from low tide to just above the mean high tide. Beaches with coarse sediment with large space between the pebbles have a strong swash but a weak backwash as water trickles between the stones. This pushes material up the beach making it steeper. Beaches with fine sands have a strong backwash as water is unable to pass between the sand grains. This brings sediment down the beach resulting in a very low beach gradient, often of less than 1o.
3. Contrast drift-aligned and swash-aligned beaches. (3)
Drift aligned beaches experience longshore drift which moves sediment along the beach in the direction of the prevailing wind. Swash-aligned beaches are found between headlands where wave refraction results in sediment being moved up and down the beach in the same direction, often creating a crescent of sand.
4. With the aid of a diagram, explain longshore drift and describe how it can sort sediment by size along the coast. (6)
Longshore drift moves sediment along the coastline in the direction of the prevailing wind. As each wave breaks onto the beach the swash carries sediment up the beach in the direction of wave movement. The retreating water, or backwash, carries the sediment down the beach at right-angles to the slope under the influence of gravity.
This process repeats with each wave and sediment os moved along the beach and becomes smaller and more rounded as a result of abrasion and attrition. The finest sediment is carried furthest and fastest so the beach sediment becomes sorted by size along the shore.
5. Explain why beaches on the English Channel and south coast of England may receive more constructive waves than the coastlines of the North Sea on the east coast. (6)
The longest fetch for waves arriving along the south coast of England is many thousands of kilometres from across the Atlantic Ocean. This is the direction of the prevailing wind. The energy imparted to the waves by these steady winds helps create waves with a great distance between crests. These so-called constructive waves surge on the shore carrying material up the beach when they break. As the North Sea is relatively narrow, winds blowing from the east or north-east tend to create waves with a short length and relatively high height. These destructive waves plunge down onto the shore and can carry material away from the beach.
6. Explain the impact on the width of beaches of building sea defences further up the coast, which prevent longshore drift. (4)
Sea defences which prevent longshore drift, such as groynes may have a significant impact on the beaches along the coast. Groynes, which are long wooden walls built perpendicular to the coastline, work by preventing the movement of sediment by longshore drift past each groyne wall. While groynes may be successful in maintaining a wide beach where they are built, they prevent the movement of sediment down the coast. As a result, those beaches without groynes become narrower as longshore drift still affects them. Sediment is removed but not replaced from sources further up the coastline.
7. With reference to an example, describe the formation of a sea spit. (4)
Dawlish Warren is a spit on the Dorset coast close to the Village of Dawlish. Longshore drift carried sediment along the coast from west to east. When it reached the mouth of the River Exe the sediment was deposited on the seabed slowly building up a thin finger of land out into the river mouth. Over time this spit was made wider by the deposition of more sediment and stabilized by vegetation. Further extension of the spit eastwards was prevented by river flow from the Exe. However, wave refraction and changing wind direction have acted to give the spit a recurved or hooked end.
8. What is meant by the term destructive wave? (4)
A destructive wave is one which has a relatively high wave height (distance between the wave crest and wave trough) compared to its wavelength. As a result of their short length, they tend to break along at the coast at a frequency of 10-14 per minute. The choppy shape of the wave creates condition off the coast called sea rather than gentle swell. On breaking onto coastline the wave plunges down onto the beach. This weakens the swash although it may through sediment high above the water to raise a storm beach. A stronger backwash can carry sediment off the beach to deposit a little way out as a longshore bar.
5. Explain why beaches on the English Channel and south coast of England may receive more constructive waves than the coastlines of the North Sea on the east coast. (6)
The longest fetch for waves arriving along the south coast of England is many thousands of kilometres from across the Atlantic Ocean. This is the direction of the prevailing wind. The energy imparted to the waves by these steady winds helps create waves with a great distance between crests. These so-called constructive waves surge on the shore carrying material up the beach when they break. As the North Sea is relatively narrow, winds blowing from the east or north-east tend to create waves with a short length and relatively high height. These destructive waves plunge down onto the shore and can carry material away from the beach.
6. Explain the impact on the width of beaches of building sea defences further up the coast, which prevent longshore drift. (4)
Sea defences which prevent longshore drift, such as groynes may have a significant impact on the beaches along the coast. Groynes, which are long wooden walls built perpendicular to the coastline, work by preventing the movement of sediment by longshore drift past each groyne wall. While groynes may be successful in maintaining a wide beach where they are built, they prevent the movement of sediment down the coast. As a result, those beaches without groynes become narrower as longshore drift still affects them. Sediment is removed but not replaced from sources further up the coastline.
7. With reference to an example, describe the formation of a sea spit. (4)
Dawlish Warren is a spit on the Dorset coast close to the Village of Dawlish. Longshore drift carried sediment along the coast from west to east. When it reached the mouth of the River Exe the sediment was deposited on the seabed slowly building up a thin finger of land out into the river mouth. Over time this spit was made wider by the deposition of more sediment and stabilized by vegetation. Further extension of the spit eastwards was prevented by river flow from the Exe. However, wave refraction and changing wind direction have acted to give the spit a recurved or hooked end.
8. What is meant by the term destructive wave? (4)
A destructive wave is one which has a relatively high wave height (distance between the wave crest and wave trough) compared to its wavelength. As a result of their short length, they tend to break along at the coast at a frequency of 10-14 per minute. The choppy shape of the wave creates condition off the coast called sea rather than gentle swell. On breaking onto coastline the wave plunges down onto the beach. This weakens the swash although it may through sediment high above the water to raise a storm beach. A stronger backwash can carry sediment off the beach to deposit a little way out as a longshore bar.
