Coastal Processes: Lecture 16-19 Flashcards
What are the four controls that determine the character of a coastline at any given time?
- Geology
- Wave climate
- Sea level
- Daily processes
How has the PGMT influenced the beaches we see today?
The Pleistocene Glacial Maximum was the last glacial maximum. The ice melted leading to rapid sea level rise, severely pushed back the coastline of Australia
What factors are responsible for the formation of waves?
Wind velocity, duration and fetch (the uninterrupted distance over which the wind blows across a body of water without any significant obstruction)
What types of waves can be described based on their period?
- Wind waves (Waves that are in the process of generation; locally generated, Short period)
- Swell waves (Waves that have left the zone of generation and have travelled long distances; they have large wavelengths and are very regular)
What is the primary mechanism that causes the formation of nearshore currents?
Forcing: Surf zone currents are directional flows of water that are forced by:
* Spatial and temporal variability in wave breaking
* Generally stronger with larger H and breaking intensity (H = wave height)
Describe the different types of rip currents
- Channelised Rips occupy deeper channels between sand bars and can be persistent in location for days, weeks or months. Most ‘commonly’ observed and can occur on both low/high wave energy beaches
- Boundary Rips flow next to physical structures like headlands, reefs, structures. Persistent in location and usually occupy a deeper channel. Often flow faster and further offshore than channelised rips
- Flash Rips are controlled only by the wave characteristics and by ‘vorticity’ caused by wave breaking. Common rips that are short-lived and variable in location (i.e. mobile in space and time); very few measurements.
- Mega Rips form during large storms and cause significant beach erosion
Describe the control that sediment grain size exerts on a beach.
- Coarse = steep slope (5−10°)
- Fine = gentle slope (1−3°)
How does the formation of a beach berm and beach scarp differ?
- Berms: Depositional accumulation of sand at high tide limit
- Scarps: Erosional notch caused by large waves, higher tides
Describe differences between different types of beaches.
DISSIPATIVE BEACHES (D)
* High energy beach type
* fine sands, big waves, wide surf zone, no rips
REFLECTIVE BEACHES (R)
* Low energy beach type
* coarse sand, low waves
* steep, narrow beaches with no surf zone, bars, rips
INTERMEDIATE BEACHES
* Characterised by bars and rips, medium waves, medium-sized sediments and instability (change all the time)
Describe the stages of evolution of different types of coastal dunes
- Incipients are ephemeral and form at the back of beaches (spinifex vegetation)
- Foredunes start to transgress (move landward) when de-stabilised
- Transgressive dunes: Transgressive dunes need higher energy beach states (e.g. RBB and LBT), happens when dunes destablisise.If the wind stops, the blowout dune stabilises and transgression slope (deactivated vs activated) OR
Blowout -> parabolic
What are the differences between estuaries and deltas?
- An estuary is a partially enclosed coastal body of water where freshwater from rivers and streams meets and mixes with saltwater from the ocean
- Estuaries form where river mouths or coastal areas experience tidal influences, causing mixing of freshwater and seawater. This includes sediment deposition.
Why are rocky coasts more diverse in landforms than sandy coasts?
Rocky coasts are erosional whereas sandy coasts are depositional. Landforms can depend on geology (how hard it is to erode, strengths of rock)
Why is water depth considered a coastal hazard?
Some people can’t swim + impact injuries (e.g. diving in shallow water)
How do rip currents compare as a hazard to other natural hazards in Australia?
They take many lives due to lack of education and their unpredictability. Thy are a big hazard by definition (taking lives and destroying property)
How are tsunami formed and how do they manifest themselves when they break on a coastline?
Tsunamis are formed by sudden and significant disturbances such as underwater earthquakes. These disturbances generate waves that travel across the ocean at high speeds. As the waves approach shallower waters near the coast, their speed decreases, and their height increases significantly due to wave shoaling. This results in towering waves that can flood coastal areas, causing severe damage and inundation. The waves often consist of multiple surges, with the largest waves arriving minutes to hours after the initial disturbance.
