1. Chapter 11: The Coast: Beaches and Shoreline Processes

2. Coastal region
Shore between low tide and highest elevation affected by storm waves
Coast from shore to farthest inland ocean features
Fig. 11-1

3. Beach Actively changing
Shore: backshore, foreshore, nearshore, offshore
Berm, beach face, longshore bar, longshore trough
Fig. 11-1

4. Beach composition and shape
Locally available material
Coarser sediment
Beach steeper
Finer sediment
Beach more gentle

5. Sand movement Swash and backwash
Sediments moved up and down beach face
Smaller, low energy waves sand moved up beach face
Summertime beach
Larger, high energy waves sand moved off shore
Wintertime beach

6. Sand movement Longshore current Longshore drift or transport
Parallel to shore
Increasing strength
More wave energy
Higher wave frequency
Steeper beach
Greater angle
Sand movement

7. Longshore current main way sediments moved along coasts
Southward along both U.S. coasts most of the time

8. Erosional-type shore Headlands eroded Wave-cut cliffs
Sea arches
Sea stacks
Wave-cut cliffs
Sea caves
Tectonically active coasts
Example Pacific coast U.S.

9. Depositional-type shores
Sediments re-distributed by ocean processes
Typical in tectonically passive areas

10. Depositional features
Spit
Tombolo
Bay barrier or baymouth bar
Fig. 11-7

11. Barrier islands Ocean beach Dune Barrier flat High salt marsh
Low salt marsh
Lagoon
Rising sea level pushes barrier island landward
Fig

12. Deltas Rivers deposit sediment at coast
FIG b
Rivers deposit sediment at coast
If more fluvial influence than ocean influence
Bird’s foot delta
If more ocean influence than river influence
Arcuate delta

13. Shepard classification of coasts
Primary
Geologically youthful
Controlled by non-marine processes
Examples
“Drowned” river or glacial valleys
Volcanic coasts
Coasts shaped by recent tectonic movements

14. Secondary coasts Geologically mature Controlled by marine processes
Tectonically passive
Examples
Straightened coasts
Coral reefs
Marsh grass
Fig f

15. Emergent coasts Uplift or sea level drops Once marine is now land
Marine terraces
Stranded beach deposits

16. Submergent coasts Subsidence or sea level rises
Once land (or shallower) is now underwater (or deeper)
Drowned beach deposits
Drowned river/glacial valleys
Submerged dunes

17. Tectonic and isostatic changes
Tectonic uplift and subsidence
Larger scale: major parts of continents
Smaller scale: local deformation
Isostatic adjustments to loading
Sediments or ice
Regional and local effects
Affect sea level

18. Eustatic changes in sea level
Global
Changes in spreading rates of ocean floor
Changes in ice volumes
Changes in ocean temperature
Global warming
Sea level rises
Ice melts, ocean warmer
Fig

19. Atlantic coast of U.S. Mainly submergent Barrier islands
Glaciers shaped some shorelines
Eroding coasts
Subsidence in most areas

20. Gulf coast of U.S. Mainly submergent Barrier islands Mississippi delta
High rates of erosion
Tectonic subsidence

21. Pacific coast of U.S. Mainly emergent Less erosion
Mainly rocky shoreline
Dams on rivers beach starvation
Tectonically active

22. U.S. coastal erosion, deposition
Fig

23. Hard stabilization Groin and groin field Jetty similar
Perpendicular to shore
Traps sand between groins
Interrupts longshore current
Jetty similar
Built to protect harbor entrance
Sand on upcurrent side

24. Breakwater
Parallel to shore
Offshore
Deposition behind breakwater

25. Erosion enhanced seaward of wall Seawall destroyed Beach narrowed
Built on beach
Parallel to beach
Erosion enhanced seaward of wall
Seawall destroyed
Beach narrowed
Fig

26. Alternatives to hard stabilization
Limit construction near shore
Relocate businesses/homes destroyed by wave erosion

27. End of Chapter 11: The Coast: Beaches and Shoreline Processes