Announcements
¤  Lab 1 due on Friday
¤  New extra credit opportunities posted
¤  Explore a saltwater beach, visit the Ballard Locks, ride the ferry (2
pts. each)
¤  Keeping up the headlines (1 pt. each)
¤  Be the next Bill Nye (up to 10 pts.)
¤  No lab next week
¤  Visit Seattle Aquarium
¤  Pick up ticket before or after class
¤  Monday (10/7) is last day to pick up ticket
¤  Lab and Case Study posted
¤  Case Study due in class on Friday, 10/11
¤  Lab due in class on Friday, 10/18
1
Do you really want to buy that
beachfront house?
¤  Recognize the different types of coasts
¤  Describe the processes that change the shoreline
¤  Beach anatomy
¤  Seasonal changes
¤  Longshore transport
¤  How do the structures we build change the shoreline?
This week we will study the
types of coasts and
beaches and the natural
processes that create and
maintain them
2
Anatomy of a beach
¤  Berm: ledge or terrace with flat tops
¤  Beach face: seaward slope, dependent on sediment type and
wave energy
¤  Troughs and bars run parallel to beach
Fig. 12.6
3
Beach: River of Sand
STUDY QUESTIONS
¤  Describe the seasonal changes that occur on a beach? Explain the
cause for the changes between winter and summer months.
¤  What are “longshore currents”? What causes them? ¤  Explain the role of submarine canyons in sediment transport. ¤  List and explain two ways people can affect beaches.
¤  How can breakwaters parallel to shore affect sediment transport or
deposition? Can you illustrate your explanation with a diagram?
4
Beaches: River of Sand
Up to beach tank
Minute 7
5
Seasonal Beach Changes
The small waves of summer move
sand from offshore to the beach
and form a summer berm
The high waves and storms of
winter erode sand from the
beach and store it in offshore
bars.
Summer Profile
Winter Profile
Winter conditions remove the
summer berm, leaving only the
winter berm on the beach.
Fig. 12.19
6
Sands shift with the seasons
¤ Most beaches in WA consist of
a shallow covering of sand or
gravel over rocks
¤ Winter:
¤ Summer:
At South
Whidbey State
Park, sand bars
cover the lower
portion of the
gravel beach.
Sand moves
with the
seasons and
storms,
sometimes
covering much
of the beach,
other times
being drawn
offshore
7
Beaches: River of Sand
Up to N. America Map
Minute 12
8
How do waves move sediments?
¤  Wind = waves
¤  Breaking wave = turbulence
¤  Swash moves sediment onshore diagonally
¤  Backwash moves sediment straight down beach
¤  Swash + backwash = zigzag
Why do waves
bend as they
come onshore?
Fig. 12.20
9
How do waves move sediment?
¤  Winds blow, waves form
¤  As a wave approaches shore, it feels the bottom (surf zone)
¤  Speed changes, wave steepens and begins to break
¤  The turbulence generate from the breaking wave tumbles beach material
(beach absorbs some of the waves energy)
¤  The “stronger” or more energetic a wave is, the more sediment it stirs up
and tumbles
¤  Waves moving toward shore transport sediment onshore (called onshore
transport)
¤  Wave angle results in the transport of sediment parallel to shore
¤  Up-rush or swash from breaking waves moves sediment diagonally up and
along beach in direction of longshore transport
¤  Backwash moves sediment downslope
10
Sources & Sinks
¤  Longshore transport is interrupted by obstacles
¤  Natural
¤  Manmade obstacles
¤  Shoreline divided into "drift sectors”
¤  Sources?
¤  Sinks?
11
Sink or Source?
Source:
Sink:
Direction of drift or longshore transport:
spit
bluff
12
Understanding Beach Evolution
¤  Summer:
¤  Waves tend to be gentle & transport sediment
landward
¤  Beaches widest
¤  Winter:
¤  Storms at sea produce larger waves that erode
beaches & transport the sediment seaward
¤  Longshore transport alters the shape and profile of a
beach
¤  Where wave action is strong, sediment is eroded and
transported
¤  Where wave action is reduced, sediment is deposited
13
Human intervention in natural beach
evolution
Wave action and
longshore transport can
erode beaches and be a
hazard to boat harbors
People have taken
measures to minimize
those undesirable effects
(with mixed results)
¤ Build structures to stop beach
erosion and stabilize beaches
¤ Jetties, groins, seawalls
¤ Build structures to protect
harbors
¤ Breakwaters
¤ Building dams
14
Beaches: River of Sand
To end
15
Test your knowledge
¤  Can you identify the “parts” of a beach?
¤  Can you describe how a beach changes from summer to
winter conditions?
¤  Width?
¤  Berms?
¤  Slope?
¤  Sediment type?
¤  Can you describe how waves move sediment along the
shoreline (longshore transport)?
¤  Can you identify sources and sinks of sediment to a beach?
16