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.
What is the sequence of waves transformation over cross-shore profile.
Off shore: shoaling → As it reaches the nearshore, right above a bar: breaking waves → In the foreshore: bores → at the edge of the beach: swash
What is shoaling?
Waves will continue to travel in their direction of propagation with little loss of energy.
Shoaling is the deformation of waves once they start approaching the shore and reach 1/2L:
- slow down as they start to feel the bottom
- This causes wavelength to decreases, but period is same, and waves get steeper and taller
( the bottom of the waves slow down relative to the top, so the crest overtakes the trough and THEY BREAK!!!)
What are the different types of breaking waves?
Spilling: Most common, only top part of wave curls over, wave breaks over a distance, and occurs on flat shorefaces.
Plunging: wave peaks up until it’s an advancing wall of water. Crest advances faster than base of breaker, curls, and then descends violently into trough, can make an explosive sound when trapped air escapes from wave. Occurs on medium to steep sloping beaches.
Surging: advances at the same rate as the base of the wave, it surges up the beach as a wall of water. It may or may not be accompanied by white water, and is usually found on very steep beaches.
What is wave swash? What is the wave run-up level?
Wave swash: when water rushes up the beach. The slope of the beach limits how far the swash can travel up the beach, and returning to ocean is “backwash”.
Wave run-up level: the max level the waves can reach on the beach
What are the causes of wave refraction? What does it do?
Caused by interation of waves with:
- sea floor
- shoals and islands
- currents
Wave refraction erodes and smooths coastlines. It acts to straighten them by concentrating wave energy on headlands. This occurs over LONG timescales.
What are the wave-dominated landforms? What about the erosional wave-dominated landform?
Spits: A long narrow accumulation of sand with one end jointed to mainland and the other projecting out to sea or across an estuary. Its tip is recurved due to wave refraction, elongated due to longshore drift, and a depositional landform.
Barrier islands: an offshore, narrow sand bar that runs parallel to the hinter lying coast. It’s depositional.
Cliffs (erosional): Steep slopes that border ocean coasts. They are typically formed by erosion or major debris avalanches. Cliff erosion is mainly controlled by rock hardness.
Critical processes in this are: mass movement, weathering, rock removal process (done by destructive waves)
In tide-dominated coasts you can find…
Estuaries: partially enclosed, coastal water bodies where freshwater from rivers and streams mixes with salt water from the ocean. The river flow and sediments mix with sea water in a large coastal embayment
Salt marshes: coastal ecosystem in the upper intertidal zone, between land and open saltwater or brackish water, that is regularly flooded. They occur worldwide, particularly in middle to high latitudes and are common in estuaries.
Mangroves: group of trees and shrubs that live in the coastal intertidal zone. They are common in warmer climates where they provide habitat for species and stabilize coastlines.
Describe the simultaneous processes occurring in a high latitude coast with the current, changing climate
Increase in global temperatures causes battling forces between:
- Glacial retreat
- Increasing meltwater and fluvial discharge that makes its way to the ocean
- Permafrost degradation which increases the depth of the active layer
- which in turn, causes more cliff erosion by waves and thermokarst
What are berms, beach ridges, and ridge plains?
Berms: are active ridges parallel to the shoreline formed by swash processes.
Beach ridges: inactive berms parallel to the shoreline
Ridge plains: several beach ridges aligned parallel to the coast, they can be used to reconstruct past sea levels. Berms accumulate every time the sea level drops.
