Your SlideShare is downloading. ×
Ga Dawlish 2012
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

Ga Dawlish 2012

534
views

Published on

Published in: Education

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
534
On Slideshare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
0
Comments
0
Likes
0
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. Understanding coastal processesand problems to produce successful management solutions. A case study of Dawlish Warren. Dr. Chris Spencer University of the West of England, Bristol
  • 2. Shallow Water Waves :• Waves change as they move into shallow water• motion of water molecules changes http://www.oceanpix.co.uk/wave-simulator.htm
  • 3. Moving into shallow water the sea floor starts to interfereAs water shallows wavelength and wave velocity decrease• wave height increases• wave steepens• crest becomes narrower and steeper, can’t continue• the wave breaksThe point at which this happens variesHow does this vary on steep / shallow beaches?
  • 4. The wave breaks :• water runs up the beach until stopped by gravity – the swash• water then flows back down the beach due to gravity – the backwash
  • 5. Beaches : Shore Normal Morphology : • beach – loose pile of sand and gravel • survives in high energy environment…….walls get destroyed?? How do beaches survive? • beaches are mobile • adapt shape to conditions • walls are fixed Low energy conditions (summer) – beach relatively steep - reflective – waves break onto the beach, relatively well spaced out – backwash returns before the next swash – swash not slowedLecture 3 : Dr Chris Spencer
  • 6. How will this effect sediment movement? Beach Shape? – these are constructive waves – give us summer profiles – berms at the back of the beach Under high energy conditions (winter) – beach slope is more gentle – absorb / dissipate – spilling breakers, breaking over beach – waves arrive in rapid succession – backwash interferes with the next swash – reduced ability to move seidmentLecture 3 : Dr Chris Spencer
  • 7. • net seaward movement of sediment – destructive waves – winter profile – wider flatter beach Beach shape is also influenced by particle size • this is due to the variable permeability • coarse beaches are more permeable • swash dominates, backwash returns through the beach • net sediment movement up the beach – increases gradientLecture 3 : Dr Chris Spencer
  • 8. Longshore currents : • waves may approach the coast at angle • usually <100 due to refraction • swash approaches at an angle • backwash returns with gravityDr Chris Spencer : Lecture 3
  • 9. Longshore Drift : • wave process leads to characteristics landforms • landforms become detached from the coast Spits – narrow, elongate beaches – detached from the coast • longshore drift transports sediment along the coast • where the coast is ‘indented’ some of this sediment is deposited • the longshore drift can now extend furtherLecture 3 : Dr Chris Spencer
  • 10. The spit then extends across the indentation in the coast • can extend right across bay bar – if an estuary the high discharge will keep this open • spits have a characteristic hook shape at the end, a recurve • often a whole series of recurves visible Example : Dawlish Warren 2 theories – waves approach and slow in the shallows – curve around the spit – angle of the wave varies – builds up a recurveLecture 3 : Dr Chris Spencer
  • 11. Profile 1 Profile 2 9 9 8 8Height (m) 7 7 Pre-storm Height (m) 6 Post-storm 6 5 5 4 0 20 40 60 80 4 0 20 40 60 80 100 Distance along transect (m) Distance along transect (m) Profile 3 Profile 4 9 8 9 7 8 7 6Height (m) Height (m) Pre-storm 6 5 Post-storm 5 4 4 3 0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 140 Distance along transect (m) Distance along transect (m)