1. The Coast: Shoreline Processes

2. Sand movement along beach
Perpendicular to shoreline (toward and away)
Swash and backwash
Parallel to shoreline (up-coast or down-coast)
Longshore transport

3. Swash and backwash
After wave breaks, up rush of water (swash) on beach
Sediment moved toward land
Backwash
Water returns to ocean
Sediment moved away from shore

4. Swash and backwash Light wave activity Fair weather Summertime beach
Swash dominates
Sediment moved toward shore
Wider beach
Fair weather
Summertime beach

6. Swash and backwash Heavy wave activity Sand forms offshore sand bars
Backwash dominates
Sediment moved away from shore
Narrower beach
Sand forms offshore sand bars
Stormy weather
Wintertime beach

8. Seasonal Change
Summer: waves have a short wave height and a long wave length.
Low energy
Swash dominates
Summer berm (builds the beach)
Erodes offshore sandbars
Winter: wave height increases and wave length decreases.
High energy
Backwash dominates
Winter berm (erodes the beach)
Builds offshore sandbars

9. Longshore current
The longshore current occurs when waves strike the beach at an angle.
Wave refraction causes water and sand to move parallel to shore
Zigzag motion in surf zone
Longshore current – a current running parallel to shore caused by waves approaching the beach at an angle
Longshore transport (drift) – movement of sediments parallel to shore, driven by wave energy

11. longshore current longshore drift swash backwash
______________(net movement of water)
longshore current
longshore drift
swash
backwash

12. longshore current
longshore drift (longshore transport)

13. Longshore transport Millions of tons of sediment moved yearly
Direction of transport changes due to wave approach
In general, sediment transported southward along Atlantic and Pacific coasts of U.S.

15. Rip Currents
A very strong, narrow surface current that flows seaward through the surf zone caused by the escape of excess water
Not rip tides!
High energy beaches
Swim parallel to shore 15

16. Coastal Cells
Sections of coast in which sand input and sand output are balanced are referred to as coastal cells.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.

17. Human Interference on Coastal Processes
Structures built to decrease coastal erosion and interfere with sand movement
Often results in unwanted outcomes
Some structures may increase wave erosion

18. Groins and groin fields
Human Interference on Coastal Processes
Groins and groin fields

19. Human Interference on Coastal Processes
Jetties

20. Human Interference on Coastal Processes
Breakwaters

21. Human Interference on Coastal Processes
Seawalls

22. Human Interference on Coastal Processes
Importing Sand