Coastal Sediment

Question 1

How are rivers a source of sediment?

Answer 1

Sediment that is transported in rivers often accounts for the vast majority of coastal sediment. Especially in high rainfall environments where active river erosion occurs. This sediment will be deposited in river mouths and estuaries where it will be reworked by waves, tides and currents

Question 2

How is cliff erosion a source of sediment?

Answer 2

This can be important locally in areas of soft rocks. The extensive tall cliffs along the holderness coast in Lincolnshire comprise of sand and clay and rates of erosion can be as high as 10m a year. This contrasts with the tough, igneous granites in Cornwall that erode at very slow rates

Question 3

How is offshore sediment a source of sediment on the coastline?

Answer 3

Can be transferred into the coastal zone by waves. In the uk, sea levels rose at the end of the last glacial periods, resulting in a large amount of course material being bulldozed onto the south coast of England to form landforms. Storm surges associated with tropical cyclones/ tsunami waves can be responsible for inputs of sediment too

Question 4

How does wind affect sources of sediment at a beach?

Answer 4

In glacial or hot arid environments, wind blown sand can be deposited in costal regions. Sand dunes are semi dynamic features at the coast that represent both accumulation of sand and potential sources

Question 5

What is a sediment cell?

Answer 5

A stretch of coastline within which sediment movement is more or less contained. These all are generally bordered by 2 large headlands or deep water and contain inputs, transfers and stores of sediment

Question 6

How many sediment cells are there in the uk?

Answer 6

11 cells, further divided into sub cells

Question 7

What are transfers (flows) at the coast?

Answer 7

Longshore (littoral) drift as well as onshore and offshore processes such as winds and currents

Question 8

What are sinks (store) at the coast?

Answer 8

Beaches, sand dunes and offshore bars/banks/bands

Question 9

Mini CS: why are erosion rates high at Flamborough head?

Answer 9

• characterised by soft limestone and chalk cliffs, more susceptible to weathering and erosion compared to harder rock types
• consistent action of waves from the North Sea contributes significantly to coastal erosion, as energy from the waves can undercut the cliff

Question 10

CS: where might most stored sediment be found?

Answer 10

• typically found in the bays and coves along the coastline. These areas act as natural deposition zones where sediment carried by waves and currents can settle
• the beaches at the base of the cliffs can accumulate sediment aswel, especially during calmer weather conditions where wave energy is lower

Question 11

CS: what are the 2 major sources of sediment for this cell?

Answer 11

Rivers = rivers flowing into the sea carry sediment from inland areas, which are then deposited along the coastline
Coastal erosion = the erosion of the cliffs at flamborough head itself contributes significantly to sediment supply as the soft limestone and chalk cliffs erode, they release material that is transported by waves and currents

Question 12

Why are human changes to sediment locations an issue?

Answer 12

• disrupting what’s in a sediment cell (changes what should be a closed system), as material wont naturally come back
• adding/removing sediment unbalances the equilibrium