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Beaches & Shoreline Processes

Beaches & Shoreline Processes. Landforms and terminology in coastal regions. the foreshore - the area most influenced by the high and low water marks and breaking waves. the backshore - submerged only during the highest tides and severest storms.

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Beaches & Shoreline Processes

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  1. Beaches & Shoreline Processes

  2. Landforms and terminology in coastal regions • the foreshore - the area most influenced by the high and low water marks and breaking waves. • the backshore - submerged only during the highest tides and severest storms. • the berm – the high point on the beach; the backshore-foreshore boundary. It changes seasonally.

  3. Landforms and terminology in coastal regions Notch Berm Beach face Wave-cut bench Longshore bar

  4. Light versus heavy wave activity

  5. Summertime and wintertime beach conditions Summertime beach Wintertime beach

  6. Movement of sand on the beach Movement parallel (↔) to shoreline • Caused by wave refraction (bending) • Each wave transports sand either upcoast or downcoast • Huge volumes of sand are moved within the surf zone • The beach resembles a “river of sand”

  7. Beaches & Shoreline Processes • Erosion • Deposition • Human Development

  8. Longshore current and longshore drift • Longshore current = zigzag movement of water in the surf zone • Longshore drift = movement of sediment caused by longshore current

  9. Features of erosional shores • Headland • Wave-cut cliff • Sea cave • Sea arch • Sea stack • Marine terrace

  10. Headland Eastern tip of Oahu

  11. Wave-cut Cliff Ka‘ula

  12. Sea Cave w/collapsed roof Na Pali Coast, Kauai

  13. Sea arch Sea stack (collapse of sea arch) Puu Pehe (Sweetheart Rock) on the island of Lanai. Chain of Craters Rd., HI

  14. Sea Arch and Sea Stack

  15. Marine Terrace Haunama Bay

  16. Features of depositional shores • Spit • Bay barrier • Tombolo • Barrier island • Delta

  17. Spit

  18. Barrier Bay

  19. Tombolo Poipu Beach Park Kauai

  20. Formation of barrier islands • Sea level rose after the last Ice Age • Caused barrier islands to roll toward shore like a tractor’s tread

  21. Barrier Islands • Features: • Ocean beach • Dunes • Barrier flat • High salt marsh • Low salt marsh • Lagoon

  22. Barrier Beaches Red Sands Beach, Maui

  23. Barrier Islands

  24. Deltas • Feature: • Triangle deposit of sediment Nile River Delta Mississippi Delta

  25. Features of Submerging Shorelines • Changes in Sea Level: • Tectonic movement • Isostatic adjustment • Worldwide (eustatic) changes in sea level • Ice ages • Global warming

  26. Composition of Beach sand in Hawaii: • Coral • Shells • Sponge spicules • Calcareous algae • Volcanic particles • Shark teeth

  27. White Sand Beach

  28. Black Sand Beach Big Island

  29. Green Sand Beach Big Island Mahana Bay, HI

  30. Red Sand Beach Maui

  31. Origin of Dunes • An abundant supply of loose sand in a region devoid of vegetation • A wind energy source sufficient to move sand grains • A topography whereby sand particles lose their momentum and settle out

  32. Beach Flora Vegetated dune, Kanaha, Maui.Naupaka shrub and 'aki'aki and pohuehue (with purple flowers) ground cover at center, 'aki'aki (sparse ground cover) in background.

  33. Close up of 'akulikuli. Photo from JOHNSTONE, 1997. Close up of 'aki'aki. Photo from JOHNSTONE, 1997. Close up of pohuehue, Honokahua, Maui Common name: beach morning glory

  34. Beach Fauna

  35. Sea-Level Rise Wave/Current Action Coastal Erosion Sediment Deficiencies • Sand mining • Dune grading • Sand impounding (behind shoreline structures) • Water quality degradation • Harbor/navigational channel construction

  36. Beach Erosion

  37. Types of hard stabilization • Hard stabilization perpendicular to the coast within the surf zone: • Jetties—protect harbor entrances • Groins—designed to trap sand • Hard stabilization parallel to the coast: • Breakwaters—built beyond the surf zone • Seawalls—built to armor the coast

  38. Shoreline Hardening: Groin

  39. Shoreline Hardening: Groin

  40. Shoreline Hardening: Jetty

  41. Shoreline Hardening: Breakwater Magic Island is a peninsula shooting off from Ala Moana Park. The beach is protected by a man-made breakwater that cuts off the action of the surf while allowing enough water circulation to keep the salt water fresh and clean.

  42. Shoreline Hardening: Seawall Waikiki Beach from the Halekulani Hotel.

  43. Lanikai

  44. Beach Restoration Lanikai

  45. Beach Replenishment Kohio Beach 10,000 cubic yards of sand pumped from off shore

  46. Beach Replenishment Kohio Beach

  47. Beach Replenishment Kohio Beach

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