2.4. Sediment Sources, Cells And Budgets

Question 1

How are rivers a sediment source?

Answer 1

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 and sediment source?

Answer 2

Important locally in areas of soft or unconsolidated rocks
Extensive cliffs along the Holderness comprise sand and clay and rates of erosion can be 10m per year
Type of rock determines how much sediment there is

Question 3

How is longshore drift a sediment source?

Answer 3

Sediment is transported from one stretch of coastline to another stretch of coastline

Question 4

How is wind a sediment source?

Answer 4

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

Question 5

How are glaciers a sediment source?

Answer 5

Ice shelves cave into the sea, depositing sediment trapped within the ice
Large chunks of ice with sediment within them

Question 6

How is offshore a sediment source?

Answer 6

Sediment from offshore can be transferred into the coastal zone by the waves, tides and currents. In the UK, sea levels rose at the end of the last glacial period, resulting in a considerate amount of coarse sediment being bulldozed on the south coast of England to form landforms like barrier beaches
Storm surges can be associated

Question 7

Sediment cells

Answer 7

• A stretch of coastline, usually bordered by two prominent headlands where the movement of sediment is more or less contained
• Inputs (sources): these are primarily derived from the river, coastal erosion and offshore sources, such as bars or banks
• Transfers (flows): these involve longshore drift together with onshore and offshore processes such as rip currents
• Stores (sinks): these include the beach, sand dunes and offshore deposits

Question 8

Sediment cells in England and Wales

Answer 8

• Each of the 11 major sediment cells in the UK can be divided into several smaller sub cells
• One of these sub cells is sediment cell 2 - Flamborough Head to Spurn Point
• It’s possible to identify sediment sources from the erosion of the weak and unconsolidated boulder clay
• Some material is washed offshore to form an output from the system
• Some material is moved down south as a transfer by longshore drift
• It’s then deposited to form Spurn Point as an output
• Tsunami waves = high energy changing cell

Question 9

Sediment budgets

Answer 9

• Material in a sediment cell can be considered in the form of a sediment budget (where losses and gains occur)
• Losses from the system include deposition of sediment sinks, whereas gains tend to involve coastal erosion or sediment brought into the system by rivers or offshore sources
• In principle, budget seeks to achieve a state of dynamic equilibrium- erosion+ deposition are balanced

Question 10

What are long term stores?

Answer 10

Sand dunes
Sandbanks
Beaches

Question 11

Sea defences affecting sediment budget and cells

Answer 11

Longshore drift is affected if groynes are present, disrupting cycle
Sea walls absorb energy
Gabions are protected