2: Beaches Introduction Flashcards
What are the 4 ways of defining beahes based on their position relative to the sea?
- Swash-aligned = facing oncoming waves directly
- Pocket = closely cushioned between two headlands
- Drift-aligned = aligned at an angle slightly off the oncoming waves (hence they are susceptible to longshore drift)
- Embayed = a beach that has the side nearest to the direction of the oncoming waves overshadows by a headland
What are the two extremes in terms of how a beach is influenced by tides?
Microtidal (tide dominance is much less than the dominance of waves) and macrotidal (the oppositte)
What are argus stations?
These are beach-observing computer stations that monitor the beach characteristics such as rip currents and wave direction
What are the two types of wave energy in terms of distribution?
Reflective or dissipative
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What are dissipative beaches like?
when the wave energy that the beach receives is distributed and spread out across the beach
What are reflective beaches like?
When waves surge up the beach and do not really break until they reach the beach. Once they reach the beach they do not really form waves but more cusps where the energy/water rushes up then simply sinks back in to the ocean either side of the way they arrived
When is more wave energy conserved - reflective or dissipative?
reflective
What are the 4 wave types?
Collapsing, surging, plunging, spilling
What are the 4 different beach types based mostly upon tidal range?
Wave-dominated, tide-dominated, tide-modified, beach+rock/reef flats
What is beach slope angle equal to and why?
Pythagoras - beach width and beach height
What can make calculating beach slope difficult and why?
Irregular beach slopes which are very common due to the presence of bars, berms and curved profiles
What are the 6 different wave-dominated beach types in the Short-Wright model?
Dissipative, transverse bar and rip, longshore bar and trough, low tide terrace, rhythmic bar and beach, reflective
Describe the waves at dissipative beaches outlined in SW model
Large high energy waves with short periods in between with multiple waves breaking before they reach shoreline
Describe the morphology of dissipative beaches outlined in SW model
fine sand distributed over large area causes sea bed to be flat. Occasionally bars further out are minor in significance
Describe the bar/trough morphology of longshore bar and trough beaches outlined in SW model?
continuous parallel to the beach bar with a deep trough occasionally crescentic in shape. More crescentic means more reflective and likely more rips
Describe the bar/trough morphology of rythmic bar beach outlined in SW model
similar to the the longshore bar/trough beach but it is more crescentic in shape that means more reflective and stronger/more rips
Describe the bar/trough morphology of transverse bar rip beaches outlined in SW model
More extreme rhythmic bar beach whereby the strong crescentic bar now features almost completely perpendicular troughs where rips are strong
Give an example of a beach that might be classes as rythmic bar or transverse bar rip beach (sw model)?
Hawks Nest
Describe the morphology of a low tide terrace beach outlined in the SW model
when a bar has moved so far up the beach that it becomes a terrace
Given an example of a low tide terrace (sw model) beach
Crowdy Head
Describe the morphology of a reflective beach (sw model)
Waves come in but do not break in a surf zone and instead they reach the shoreline. The beach is so steep that it reflects the incoming unbroken waves back out to sea via clear cusps preventing the water going far up the beach
What do reflective beach types feature that causes them to be so steep?
Step
What is the main thing that causes rips to form?
Troughs in the sea bed morphology
How can the rips/troughs become more intense?
The rips can funnel in to the troughs and cause increased erosion in these troughs that makes them deeper. They may become so deep that the waves never break in them
What are the the types of rip?
- channelised = located in open sections of the beach from troughs
- headlands = hug headlands or sea walls
- transient = flash rips essentially that just open up randomly
What causes the randomness of transient rips?
a few waves will come in to the beach and cause sea level to rise significantly and the shore needs to get rid of this extra water somehow
How fast do channelised rips normally travel?
30-50cm per second
How fast can channelised rips be if they pulse?
1-2m per second
Where do rips extend out to?
varies - can be far offshore or only like 10m
What is the Dean Number or Gourlay Number?
This value indicates whether the beach is reflective (<1) or dissipative (>6) or intermediate (anything between 1 and 6)
What is the Dean or Gourlay Number based upon?
breaking wave height, wave period, sediment fall velocity
What is and what is the signifcance of a beach envelope?
essentially the range for the different states that the beach can be in. Its important because we need to remember that beaches can be a range of different states (e.g. Hawks Nest)
What are 3 ways of measuring beaches?
- Emery method - essentially in-situ
- Remote sensing and GIS
- Argus
What is the accuracy of Emery, GIS and Argus methods?
Emery = 0.13m GIS = 0.03m (individual) and 0.1m (interpolated) Argus = 0.25m
What are 2 pros and 2 cons of emery method?
+ rapid and inexpensive
- labour intensive and 2D
What are 2 pros and 2 cons of GIS method?
+ high spatial density and high accuracy
- labour intensive and expensive
What are 2 pros and 2 cons of Argus?
+ allows retrospective surveying and automatic and high frequency
- limited to intertidal range and lower accuracy
