Lec #3 Beaches and Coastal Sand Dunes Flashcards
Name the eight zones of the shore
Offshore Nearshore Littoral zone Shore/Beach Forshore zone Backshore zone Surf zone swash zone
What is the offshore zone
No significant action from waves on sediment movement
What is the littoral zone?
An area where sediment is moved by wave action
What is the nearshore zone?
portion of beach profile subject to wave action up to mean low water
What is the shore / beach zone?
part of the beach subject to wave action sometimes exposed
What is the foreshore zone?
part of the beach subject to wave action in non storm conditions
What is the backshore zone?
only subject to wave action during storm conditions
What is the swash zone?
the zone of wave run-up on the beach and return water on the back wash
What is the surf zone?
the zone of broke waves extending from the break zone to the for shore
how much do sand and cobble beaches account for
Fine sand 20%
Cobbles 10%
Why are muddy coastlines not included as beaches?
Due to lack of sediment movement
Highlight the differences between a sandy and a cobble beach
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
What controls beach morphodynamics
the extent to which a beach will respond to a change in the environment, this a function of sediment size.
What is the difference in beach morphodynamics between cobble beaches and sandy beaches
The larger the sediment size the larger the change in beach profile will be, cobble beaches will undergo a greater change in the profile
Why is grain size key in beach morphodynamics?
It can control the wave characteristics which impact on wave energy as well as the interaction between the swash and the backwash
Explain the water table on beaches
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
How does the water table effect the beach berms
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
What are beach cusps and explain their formation?
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.
What controls beach cusps wave length?
Directly controlled by the size of the rip current cells
What conditions make formation of beach cusps ideal?
Steep gradient and low wave energy that allow the swash/backwash process
What are rip currents?
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
What controls the exit point of rip currents?
they look for a dip in the topography, can often occour near beach or jetties
Key points on sand dune formation (3)
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
What are the two dune systems, and explain them.
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
What are foredunes?
These will establish parallel to the sea shore, obtains sediment for the beach directly and the action of waves can play a role
What are secondary dunes?
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
Examples of dune disturbance and explanations?
can be both natural and mad made, it results in the destablisiation of sand dunes which form blowout
How does vegetation aid sand dune formation?
- increased deposition by catching of sediment
- reduces or removes the effect of wind action on the dune top by raising the boundary shear stress
What are the adaptations of early species?
Beach grasses and reeds are common and important colonizers, the must have high dispersal abilities and deep root system for water
What are adaptations of middle species?
Environment is still harsh, water and nutrient supply is not high, every green shrubs are present and high adaptation to stress levels
What are adaptions of late species?
These can be trees older than 200 years, give evidence for a fixed dune, higher nutrient requirement
How does vegetation prevent wind erosion (2)
- increase in stratum cohesiveness through introduction of minerals
- organisms act as a wind buffer
