1. Coastal Zones and Processes
Chapter 7
Coastal Zones and Processes
Coastal zones are important to the United States:
30 of the 50 states abut a major body of water (Atlantic or Pacific Ocean, Gulf of Mexico, one of the Great Lakes), and those of 30 states are home to about 85% of the nation’s population. About half of that 85% live in the coastal regions and that number is growing.

2. Figure 7.1

3. Nature of the Coastline
Factors that impact coastlines:
Tectonic setting
Materials present at the shore
Energy of water striking the coast
Active margin – associated with active plate tectonics
Often cliffs found near active margins
Passive margin – far from active plate tectonics
Often a broad shelf, beaches and with sandy offshore beaches

4. Figures 7.2 and 7.5 a and b the Coast of California

5. Figures 7.3 a and b, a beach
A beach is a gently sloping surface washed over by the waves and covered by sediment
The beach face is the portion regularly washed by the waves as tides rise and fall
The berm is the flatter part of the beach landward of the beach face

6. Nature of the Coastline
Beach – a gently sloping surface washed over by the waves and covered by sediment
Sediments are carried by longshore currents and placed on the beach by littoral drift
Waves – generated by wind are small undulations on the ocean surface
Waves move along an ocean and water molecules move only in orbits
Waves disappear below wave base
Orbits are larger nearest the surface and become smaller with depth
Once a wave ‘feels’ the bottom the orbits are interfered with and breaking occurs
Erosion of solid rock along a coast takes place because of milling
Ocean surfaces appear to move in and out relative to the shore because of tides
Tides occur because of the gravitational pull on the oceans by the moon and sun

7. Figures 7.4 a and b Waves and breakers

8. Figures 7.6 a and b Spring tides: Sun, moon, and earth are all aligned; Neap tides: When moon and sun are at right angles, tidal extremes are reduced

9. Figure 7. 7 longshore currents and their effect on sand movement
Figure 7.7 longshore currents and their effect on sand movement. Waves push water and sand ashore at an angle

10. Storms and Coastal Dynamics
Storms are caused by low pressure systems
Low pressure cause a bulge of water to form
Onshore winds, associated with storms, approach the shore with unusually high tides called a surge
The exceptional force of the wind driven waves and surge combine to erode beach faces, dunes above the beach, and sometimes cliffs behind the beach
Hurricanes are power examples of these storms

13. Fig. 7.10 consequences of storm surges

14. Emergent and Submergent Coastlines
Long-term sea-level changes often are associated with plate tectonics
Continental margins may uplift and produce an emergent coastline
Large rivers drain water and sediments from the continental interior and form large deltas in adjacent oceans
Loading of the crust produces submergent coastlines
Signs of changing relative sea level
A wave-cut platform will form at coastlines
A number of wave cut platforms is an indication of uplifting land or dropping sea level
A drowned valley can record changes in sea level also

15. Fig. 7.11 Wave-cut platforms

16. Figure 7.12 a drowned valley

17. Figure 7.14

18. Coastal Erosion and Stabilization
A rise in sea level will cause coastal erosion and will require stabilization
Sand may be needed, from dredging, to replace sand lost to long shore currents
Breakwaters, jetties, or groins act to stabilize beaches
These artificial barriers have erosion and deposition problems associated with them also
Projects to stabilize coastlines and beaches are required because of changes in sea level

19. Figures 7.15 a and b

20. Figures 7.16 a, b, and c

21. Figures 7.17 a and c

22. Figure 7.17b

23. Figure 7.18

24. Figures 7.19 a and b

25. Cliff Erosion
Waves and currents act to erode beaches and eventually cliffs
Cliffs are undercut
Cliff face then slumps or slides off into the sea
Cliff faces show landward retreat of the shoreline
Wave refraction works to erode points of land jutting out into the sea
Wave base interaction with the ocean bottom slow the progress of the wave
Wave base encounters the bottom near a jutting point before the coastline

26. Figures 7.20 a and b

27. Figure 7.21

28. Figures 7.22 a and b

29. Barrier Islands Long, low, narrow islands parallel to the coastline
Unstable environments
Easily washed over because of low relief
Sand migrates constantly with the wind
Constantly retreating landward with time

30. Figure 7.24

31. Figure 7.25

32. Estuaries
Body of water along a coastline, open to the sea, in which tides rise and fall
Often rivers bring freshwater into a mix with sea water producing a brackish water environment
Water circulation is limited
Estuaries do not tolerate major changes in salinity or chemistry of the water
Heavily impacted by pollution

33. Figure 7.26

34. Construction and Reconstruction in High Energy Environments
Coastal areas are easily damaged by major storms that frequent our oceans and seas
People have traditionally flocked to the coast to live and work
Property values are high along coastlines and at risk
Governments spend large amounts of money to maintain coastal areas
Recognize the coastal hazards: building locations

35. Figure 7.27

36. Figure 7.28a

37. Figures 7.28 b and c