Theme 7: Coastal systems Flashcards
What are the forcing factors in the coastal zone
- Sea level history
- Geology
- Climate
- Waves and tides
COASTAL CLASSIFICATION DIAGRAM
vertical axis is fluvial power increases from bottom to top, horizontal axis is relative power of wave/tide.
LOOK AT PIC VERY IMPORTANT
What is the coastal zone and what are the different regions within it?
The coastal zone is the interface between terrestrial and marine systems where all the energy transferred to the oceans is released.
From most inland to offshore we have:
- Backshore: region above the high-tide line whose beginning is marked by a berm. Behind the latter, we find dunes that can be anchored by vegetation
- Foreshore: starts at the high tide line and goes up to the breakers
- Nearshore: starts at the breakers, includes the surf zone, maybe even a sand bar below the water and continues further towards the sea as water depth increases
- Offshore: here waves first encounter the seafloor and begin to slow down.
What is the tide? What is the tidal range?
It is the rising and falling of sea level due to the gravitational forces of the Moon and the Sun and the rotation of the Earth.
Tidal range: the difference in water level between high and low water.
Describe how a process-response system applies to a coastal region
Process-response systems are systems where there is interaction between morphological and cascading systems. It shows how form and process are related, eg. the coastal zone, in which the cascading system of wave energy advances from deep water to the edge of the swash zone and is linked to various morphological features of the swallowing zone and beach.
Give an example of geomorphological evolution in the coastal zone
eg 1. The evolution of nearshore bar (generation and growth, migration and consolidation, merging of bar).
eg.2 Beach ridge planes: the accumulation of ridges indicates changes, notably the drop in sea level, throughout time. Everytime sea level drops, a new ridge forms.
Has sea level changed through time? If so how?
Over geologic time sea level has fluctuated lots. Since 1880, it has been rising.
What are isostatic sea-level changes?
They are local changes caused by subsidence or uplift of the crust related to either changes in the amount of ice on land, or to growth or erosion of mountains.
LOOK AT COASTAL MORPHODYNAMICS SLIDE PLS BABES
Know that processes are:
- external forcing (wind, waves, tides, currents)
- hydrodynamics
- sediment transport
Boundary conditions
- external forcing (wind, waves, tides, currents)
- static boundary conditions (geology, sediments)
What are the different nearshore currents
- Longshore currents: reflect the flux of energy parallel to the shoreline due to wave action
- Return flow: an average flow near the bed. Upper parts have onshore flow, near the bottom flow is seaward
- Rip currents: the return flow of water has piled up in the nearshore zone by breaking waves
What is wave action? What are waves?
Wave action = what drives coastal erosion and sediment transport
Waves are temporary changes in water level which involve a rise and fall of water level relative to the mean water level associated with the transfer of energy
What is sediment carried by in a coastal system?
- the orbital motion of water particles
- Breaking waves
- Swash processes: the rush of seawater up the beach after a wave breaks.
What are the different properties of waves (energy, etc.)
Waves possess potential energy (due to position of wave crest above wave trough) and kinetic energy *due to motion of water particles within waves)
Wave energy is generated by the frictional effect of winds moving over ocean surface.
Wavelength (L) = horizontal distance between 2 wave crests/troughs. The longer the wavelength, the faster the speed and period of a wave
Wave height (h) = vertical distance between a trough and a crest
Period = time it takes for successive wave crests to pass a point
Wave base = as a wave form passes, it disrupts the water column to a depth = 1/2 the wavelength (L) (if less than this depth, the waves feel the bottom)
What 3 factors affect the growth of wind waves?
- Wind speed must be blowing faster than the transfer of energy from crest to crest
- Amount of time the wind blows
- Fetch length: uninterrupted distance over which the wind blows without a change in direction
What are swell waves? How are they different from normal wind waves?
Swell waves are series of waves generated at a distance, sometimes referred to as “old waves”. They are longer (period wise), rounder as they change shape while losing energy, and faster than normal wind waves.
They don’t necessarily come from the direction you’re experiencing wind from.
As the wind blows, the frictional resistance of the surface of the water results in a transfer of energy from the air to the water surface and causes small ripples to form. The ripples are able to catch more and more of the wind (increased resistance because the surface area increases), and thus the
ripples become larger and larger - as long as the wind continues to blow.