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COASTLINE PROCESSES

COASTLINE PROCESSES. Pg. 43 Shoreline is the boundary between ocean/lake and land 2.) Beach is the strip of sediment that extends from low tide inland to a cliff or zone of permanent vegetation 3.) Waves erode and deposit material along the shore erode -take away

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COASTLINE PROCESSES

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  1. COASTLINE PROCESSES • Pg. 43 • Shoreline is the boundary between ocean/lake and land • 2.) Beach is the strip of sediment that extends from • low tide inland to a cliff or zone of permanent • vegetation • 3.) Waves erode and deposit material along the shore • erode-take away • deposit-leave behind Courtesy of USGS

  2. COASTLINE PROCESSES • Pg. 43 • Beach erosion is a geologic hazard - one that • costs millions of dollars to prevent and control • A. East coast - build on barrier islands • B. West coast - narrowing of beaches • -sediments are being removed

  3. COASTLINE PROCESSES Pg. 43 5. Where do wave get their energy? A. Wind B. Movement of sea floor - tsunami C. Landslides D. Volcanic explosion Waves transmit energy so they have capacity to do work As in “beaches and structures get ‘worked’ by waves”

  4. COASTLINE PROCESSES Pg. 44 6. Characteristic features of waves A. Crest B. Trough C. Wavelength Tsunami - very long wavelength Winter - longer = move sand offshore Summer - shorter = move sand onshore D. Height

  5. COASTLINE PROCESSES Image courtesy of Office of Naval Research. Another good link

  6. COASTLINE PROCESSES Pg. 44 7. The height and length depend on 3 things A. Wind speed/strength B. Duration the wind has blown C. Fetch - the distance over which the wind has blown ROGUE WAVES are extra big (sink ships)WHY??? Constructive and destructive wave interaction

  7. COASTLINE PROCESSES Pg. 44 8. How does the water within a wave move? A. Wave form moves forward, water particles move in a circular path B. At 1/2 the wavelength wavebase and lower there is negligible water motion above is when the wave touches bottom 1 wavelength Wavebase=1/2 wavelength Courtesy of NOAA

  8. COASTLINE PROCESSES • Pg. 44-45 • 9. This explains a number of things: • Wave refraction - waves bend as they hit the • shoreline at angle. Leading edge reaches base level • first and slows down. • Waves break as they approach the shore • remember wave base - surf • C. Beach drift-movement of sediments down shore • Longshore currents-causes longshore drift of sediments • Another diagram of longshore current and the • resulting drift of sediments ND pg. 363 fig. 12.34

  9. COASTLINE PROCESSES Pg. 44-45 9. This explains a number of things: continued E. ADD summer and winter beaches-constantly in flux THIS IS FOR HIGHER LATITUDES SUMMER DEPOSITION: short wavelength=pushes sand towards the beach=sandy beach WINTER EROSION: long wavelength=sand away from beach=rocky beach=sand is deposited off shore Illustrates that wave type influences beaches ND pg. 361/ fig. 12.30/12.31

  10. COASTLINE PROCESSES Pg. 45 10.Were does the material come from that forms beaches? A. Shoreline erosion - nearby land or cliff-mass wasting Courtesy of NOAA Sediment production

  11. COASTLINE PROCESSES Pg. 45 B. Erosion of the land - brought to ocean by streams Courtesy of NASA

  12. COASTLINE PROCESSES Pg. 45 11. Waves erode by: A. Impact sedimentsbashing against stone creates more sediments - sand blaster B. Pressure-waves compress water into cracks=increases pressure=more cracking C. Abrasion-sediments sliding/grinding against stone creates more sediments - sand paper D. ADD physical removal of sediments already did but is important longshore offshore-winter vs. summer ND pg. 361 fig. 12.30 & 12.31

  13. COASTLINE PROCESSES • Pg. 45 • 12. Human Effects on Coast- Trying to Control Erosion • A) Dams - store sediment behind - beaches diminished • Sea Walls and riprap - to stop cliff retreat • build on a cliff and consider it a temporary structure • erosion will win-WHY wall REFLECTS larger waves • ND pg. 354 fig. 12.22 • *Creates deeper water which allows bigger waves to hit the • wall and the wall reflects this larger amount of energy • which takes sand out to sea/away=EROSION • C) Groins - trap sand so won’t disappear • Still need artificial replacement (fig. 1)

  14. COASTLINE PROCESSES Pg.45 (continued) D) Jetties - create protection for channels for boats E) Breakwater -protection for harbor, form tombolo(fig. 5) F) Sea level rise ND pg. 353/ fig. 12.20 Know: migration distance=1000(d) So if sea level rises 4 feet WHAT WILL HAPPEN? Direction of movement an amount So if sea level lowers 2 feet WHAT WILL HAPPEN? Direction of movement an amount

  15. COASTLINE PROCESSES Pg. 46 BOTTOM LINE -YOU CAN’T CONTROL NATURE BEACH REPLENISHMENT is expensive and where do you get the sand?

  16. COASTLINE PROCESSES • Pg. 46 • Mitigation generally falls into one of the following: • Beach nourishment-bring it in and dump it • (imitates natural depositional processes) • 2) Shoreline stabilization through structures see #12 • 3) Land-use changes-”uhm… maybe we shouldn’t • build there” • People need to understand that coastal zone • development is temporary and expendable. • Keep in mind these 5 principles…

  17. COASTLINE PROCESSES • Pg. 46 • Coastal erosion is natural process • problems occur when people build structures • within the coastal zone • 2) Any shoreline construction causes change • Stabilization through engineering structures protects • the property of relatively few people at great expense • to the general public. • Structures designed to protect a beach may eventually • destroy it. • Once built, structures produce a trend in coastal • development that is difficult to reverse.

  18. COASTLINE PROCESSES QUIZ SLIDE #1 What is this feature? Which way is the longshore current/drift? SLIDE #2 How does this slide relate to beach erosion/deposition? SLIDE #3 What will be the results for each of the two pairs of waves SLIDE #4 Which wave represents summer and winter waves and WHY? Which wave will result in sand deposition and which erosion WHY HURRICANE REVIEW VIDEO?

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