Coasts

Question 1

Ocean Swell

Answer 1

• Swells are created by distant storms in ocean
• Swell is generally of a long wavelength and low amplitude
• As swell waves approach the coastline, the water depth decreases and wave height will increase (as greater friction with the seabed reduces the speed)
• Ocean swells are high energy and determine rates and mechanisms of coastal processes
• Nearshore waves= As wave start to slow and breaks

Question 2

Nearshore Waves

Answer 2

• Ocean swell may arrive at coastline via different sources, producing variations in wave height
• There is a steady increase in wave height to a maximum phase
• Waves generated by local nearshore winds generally have a period <10 seconds
• Once nearshore waves reach the coast and break, they are termed breakers

Question 3

Storm Waves

Answer 3

• Generated by strong winds from regional storms
• West coast highly prone to this from waves from Tasman sea
• Sub-tropical cyclones in South pacific Ocean cause large storm waves in Northland and EEast Coast
• South Island and lower NI experience storm waves from Southern ocean
• Storm Surge: Lower pressue systems (located offshore) and strong winds lead to storm surges. Must be aware of these and future sea level changes when planning infrastructure construction

Question 4

Wave Refraction

Answer 4

• Sea floor depth affects the swell pattern moving towards the shore
• Wave refraction is a major process controlling nearshore sediment and wave energy dynamics
• Angle between swell and submarine contours changes so that incoming waves break parallel to submarine contours- this is because as the waves arrive (the part of the wave closer to the shore is in shallower water so moves slower, whilst the part of the wave further from the shore is in deeper water so moves faster and catches up, such that the wave is parallel to the shore
• Influence of submarine bathymetry on ocean wave refraction in nearshore environments
• Wave refraction can concentrate wave energy and accelerate coastal erosion and sediment transport

Question 5

Longshore Currents

Answer 5

• Narrow shore parallel currents occur due to wave refractions
• These travel in the same direction as mean effective wave direction
• Primary mechanism responsible for sediment transport dynamics in the coastal zone
• The wave direction leads to sediment movement to the coast at an angle, however this is then followed by backwash which takes the sediment back to the sea, this continual process leads to longshore drift of sediment along the beach
• Process of sediment movement from one coastal cell to another (in longshore drift direction) by longshore currents is called longshore drifts
• This leads to major coastal erosion and deposition; may lead to spit formation

Question 6

Sea Level Rise

Answer 6

• May be eutastic (effect of water volume changes) versus isostatic (no water volume change, but land changes)
• Rising sea levels lead to increased magnitude and frequency of coastal flooding
• This is a major hazard likely to effect Auckland

Question 7

Shoreline Erosion

Answer 7

• Coastlines are high energy environments leading to major erosion and deposition of large sediment volumes
• It can be split coastlines into rocky coasts and dominated by sediments.
  1. Rocky Coasts:
   High rock resistance means that rocky coastline erosion is slow
   Typically, erosion occurs due to wave undercutting-> leads to cliff collapse
   Weak rocks have large complex landslide systems that pose major hazard to infrastructure
   Auckland contains soft rocks- soft rock cliff erosion is natural posing major danger to NZ
   Manging soft rock coastlines will slow but NOT stop coastal cliff erosion
   Coastal cliff recession is an episodic process
   Must manage single events (such as rockfalls and landslides) as these lead to major recession