Lec #3 Beaches and Coastal Sand Dunes

Question 1

Name the eight zones of the shore

Answer 1

Offshore
Nearshore
Littoral zone
Shore/Beach
Forshore zone
Backshore zone
Surf zone
swash zone

Question 2

What is the offshore zone

Answer 2

No significant action from waves on sediment movement

Question 3

What is the littoral zone?

Answer 3

An area where sediment is moved by wave action

Question 4

What is the nearshore zone?

Answer 4

portion of beach profile subject to wave action up to mean low water

Question 5

What is the shore / beach zone?

Answer 5

part of the beach subject to wave action sometimes exposed

Question 6

What is the foreshore zone?

Answer 6

part of the beach subject to wave action in non storm conditions

Question 7

What is the backshore zone?

Answer 7

only subject to wave action during storm conditions

Question 8

What is the swash zone?

Answer 8

the zone of wave run-up on the beach and return water on the back wash

Question 9

What is the surf zone?

Answer 9

the zone of broke waves extending from the break zone to the for shore

Question 10

how much do sand and cobble beaches account for

Answer 10

Fine sand 20%

Cobbles 10%

Question 11

Why are muddy coastlines not included as beaches?

Answer 11

Due to lack of sediment movement

Question 12

Highlight the differences between a sandy and a cobble beach

Answer 12

sandy beaches will have a shallower gradient and therefore shoaling will occur further out to sea, cobble beaches have a steep profile which means shoaling only occurs closer to the shore. Wave energy is also dissipated more in cobble beaches

Question 13

What controls beach morphodynamics

Answer 13

the extent to which a beach will respond to a change in the environment, this a function of sediment size.

Question 14

What is the difference in beach morphodynamics between cobble beaches and sandy beaches

Answer 14

The larger the sediment size the larger the change in beach profile will be, cobble beaches will undergo a greater change in the profile

Question 15

Why is grain size key in beach morphodynamics?

Answer 15

It can control the wave characteristics which impact on wave energy as well as the interaction between the swash and the backwash

Question 16

Explain the water table on beaches

Answer 16

Represented by the upper level of ground water that reaches the beach, it will continue under systems such as dunes due to its hydrolgic gradient

Question 17

How does the water table effect the beach berms

Answer 17

The water table gradient will change from LT to HT and therefore infiltration will begin through the beach berm, the height of the water table will control where the beach berm lies

Question 18

What are beach cusps and explain their formation?

Answer 18

Beach cusps are arch formed sediment depositions. These are a result of small rip current cells and the associated rhythmic under bars that lead to cusps opposite the rip channel.

Question 19

What controls beach cusps wave length?

Answer 19

Directly controlled by the size of the rip current cells

Question 20

What conditions make formation of beach cusps ideal?

Answer 20

Steep gradient and low wave energy that allow the swash/backwash process

Question 21

What are rip currents?

Answer 21

when wind and waves get pushed against the shore they form rip tides, the water steams along the shore until it finds an exit point

Question 22

What controls the exit point of rip currents?

Answer 22

they look for a dip in the topography, can often occour near beach or jetties

Question 23

Key points on sand dune formation (3)

Answer 23

Sediment deposited inland dune to wave action
High sediment budget, the beach is the source and the waves are the sink
Coastal dunes normally compromise of sediment no bigger than 1.5mm

Question 24

What are the two dune systems, and explain them.

Answer 24

Impeded dunes - largely fixed by vegetation these are older dunes
Transgressive dunes -vegetation is limited and the dune is moving inshore, this will turn into a impeded dune under correct conditions

Question 25

What are foredunes?

Answer 25

These will establish parallel to the sea shore, obtains sediment for the beach directly and the action of waves can play a role

Question 26

What are secondary dunes?

Answer 26

Found landward of the primary dune systems, and the littoral sediment budget is positive, here pro-aggregation takes place and there may be intense vegetation

Question 27

Examples of dune disturbance and explanations?

Answer 27

can be both natural and mad made, it results in the destablisiation of sand dunes which form blowout

Question 28

How does vegetation aid sand dune formation?

Answer 28

• increased deposition by catching of sediment

- reduces or removes the effect of wind action on the dune top by raising the boundary shear stress

Question 29

What are the adaptations of early species?

Answer 29

Beach grasses and reeds are common and important colonizers, the must have high dispersal abilities and deep root system for water

Question 30

What are adaptations of middle species?

Answer 30

Environment is still harsh, water and nutrient supply is not high, every green shrubs are present and high adaptation to stress levels

Question 31

What are adaptions of late species?

Answer 31

These can be trees older than 200 years, give evidence for a fixed dune, higher nutrient requirement

Question 32

How does vegetation prevent wind erosion (2)

Answer 32

• increase in stratum cohesiveness through introduction of minerals
• organisms act as a wind buffer