Coastlines

• Review- Things to Know

  -Things that affect coasts

  -Coastline types & features

  -Parts of the continental margin

  -E-lines

  -Way to deal with coastal erosion
• Why Should We Care?

  About 55% (~ 3.85 billion) of the world population lives within 50 miles of a coastline
• Coasts


  -Remember- still on continental crust! (Even in the water)

  -Several forces acting on these environments (constantly changing)

  --Changing one thing will cause a ripple effect
• #1 Tides


  where water level rises and lowers a certain times of the day

  -Tidal flats: what os shown or covered during tides
• Tide Height


  Places with 'open' ocean connections have relatively little change

  -Ex: Hawaii has a tidal range of 1-2 ft

  -Ex: parts of the English coast (below)

  Restricted connections = wider tidal range

  -Ex: Bay of Fundy has a tidal range of ca 40 ft!
• #2 Waves


  Wavelength: distance between any two adjacent waves

  -Shows how far apart waves are
• Waves change as they approach shore

  -Waves slow down

  -Waves get closer together

  -Waves height increases
• wave refraction


  the bending of waves so that they move nearly parallel to the shoreline

  -One side slows down and one side stays at a higher speed
• #3- Longshore current


  movement of water that is roughly parallel to the coastline
• #4- Longshore drift


  movement of sediment

  Both at a zig zag pattern
• Shoreline Features


  Shoreline features depend on:

  -Tectonics

  -Rock type

  -Sea level fluctuations

  -Storm size/strength
• Types of Coastlines
• Emergent Coastlines:: the area is being actively uplifted

  -Due to tectonics

  -Often have tall steep cliffs close to the coastline


  Stacks- small very steep rocky islands

  -No beach at the base

  Terraces- broad flat area that form a stair step pattern as you move up the shore

  -Shows where the beach used to be in the past

  -Can track when uplift occurred
• Submergent Coastlines: often sinking , flooded with water

  -Look like coastline is broken up like islands


  Long, wide beaches & coastal plains

  -Spit- long stretched out deposit of sand that are connected to the mainland

  -Barrier Islands: long skinny deposits of sand that are not connected to the main land

  --Ocean side is eroded, mainland side os getting deposited so their location will gradually shoft
• Offshore Features


  Continental margin- area off the shoreline until you get to the part in the ocean where the continental crust ends
• Types of Continental Margins

  -Active- very close to a plate boundary; moving from one tectonic plate to another

  Ex: west coast of the United States

  -Passive- no plate bouncy Preston

  Ex: east coast of United States
• Parts of the Continental Margin

  -Continental Shelf: broad flat region where the water is still shallow

  -Continental Slope: start going down rapidly so the water is getting deeper

  -Continental Rise: area where you rise above the sea floor; marks the end of continental crust
• Coastal Erosion


  Can occur along emergent & submergent coasts
• Case Study- Cape Hatteras


  -The Outer Banks of NC

  -Strong longshore currents

  -The Cape Hatteras lighthouse

  -1868: 1500 ft inland

  -1998: just 120 ft from the ocean

  Q: What was the average rate of erosion in this area from 1868-1998?

  -To save the lighthouse, in 1999-2000 it was moved 2900 ft inland over the course of 23 days

  -Cost: $15 million
• So how do we deal with coastal erosion?
• 1st Approach: Zoning


  Build farther inland
• Setback distance


  the safe distance; how far back from the current coast can you build
• E(rosion) lines


  line along the coast marking where erosion will move the shoreline to in the future

  Ex- The E-10 line shows you where the shoreline will be10 yrs from now given the current rate of erosion
• Formula:


  (erosion rate) x (# of yrs into the future) = E-line distance

  
  

  •Ex- you want to know where the coastline will be 10 years from now

  
  

  •Given: erosion rate = 10 ft/yr

  
  

  •10 ft/yr * 10 yrs = 100 feet farther inland
• Q: How far inland should the setback distance be in order to keep buildings safe?

  National: E-60

  SC: E-40

  Q: Why doesn't SC use the national recommendation of the E-60 line?
• E-Lines & Economics


  A: Tourism. This is the #1 revenue source for SC

  2019: tourism generated ~ $24.4 billion for SC
• 2nd Approach: Barriers


  Protect the shore in one of two ways:

  -Weaken waves

  -Keep sand from moving away

  Several types of barriers are used
• Seawalls- large wall that are built parallel to the coastline

  -Weaken wakes


  Drawbacks

  -Expensive

  -Need repairs overtime

  -Can have a negative impact on tourism
• Groins: built perpendicular to the coast

  -Help with the longshore current

  -Prevents movement of sediment


  Drawbacks

  -Only one groin just pushed erosion down the shoreline

  -Expensive and require repairs nut you can't just build one
• 3rd Approach: Beach (Re)nourishment


  Replace the eroded sediment
• Case Study: Miami

  1950s

  Miami 1980s

  Worked well

  New Jersey

  1980s

  Did not work well
• Beach Nourishment


  Some wildlife issues