The Causes of Longshore Current: Figure 8 Island, N.C.

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The Causes of Longshore Current Figure 8 Island,
N.C.

• Sarah Poupalos
• Asheboro High School
• Dora Teglasy
• D.H. Conley High School

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What is Longshore Current?

• Flow of water parallel to the shore directly in
  the surf zone.
  
• Generated by waves
• Changes with wave and wind direction.

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COMPARED TO THE SWEEPING MOTION OF A BROOM
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Problem Statement What causes longshore
current?This experiment examines the processes
which affect shoreline water movement along the
coast of Figure 8 Island.
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We predicted that the following factors affected
longshore currents

• wave direction
• wave height
• wave angle
• water temperature
• tide
• surface current
• underwater current

• air temperature
• weather conditions
• wind speed
• wind direction
• time of day
• land morphology

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225 m transect

Monitored Sand Bar
Figure 8 Island
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Homebase (northern point)
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Underwater Current A Flo-mate current meter was
placed in the water at a depth of 49 cm.
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Surface Current An orange traveled along a 225 m
transect which determined the direction and
speed of surface current.
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Orange in Water
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Water Temperature A water sample was collected f
rom the surface at the water line, and
temperature was determined.
100
80
60
DEGREES
40
20
0
7/4/98
7/9/98
7/13/98
7/16/98
DATE
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Wind Speed and Direction An anemometer was place
d in the direction with maximum wind speed and
the bearing was determined using a compass.

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Determining Wind Bearing
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WIND
BEARING
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Air Temperature Temperature was monitor
ed and recorded daily with a probe.
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Foreshore Morphology Profiling from the ridge of
a migrating sand bar to the water line
documented the overall changes.
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Measuring Wave Height
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Wave Height and Number
40
70
35
60
30
50
25
40
20
of waves
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Avg. Height (cm)
15
20
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WAVES
AVG. HEIGHT
10
5
0
0
(2)
(2)
(2)
7.4
7.6
7.7
(2)
(2)
(2)
(3)
(2)
7.15
7.8 (1)
7.9 (1)
7.10(1)
7.16(1)
7.17(1)
7.14 (1)
7.13 (1)
Date
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Angle of Wave Approach The angle perpendicular t
o the wave crest was determined using a compass.

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WAVE
PERPENDICULAR
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• CONCLUSIONS
• Wind direction and speed determine wave height
  and angle
  
• Wave height and angle determine direction and
  rate of both underwater and surface currents
  
• Longshore current is one of the factors which
  moves sediment along the shoreline
  

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Acknowledgements Dr. Bill Jefe Harris Ms.
Elizabeth Moundalexis Ms. Amy Rider Mr. and Mrs.
Paul Foster Dr. Lynn Leonard (equipment) Coasta
l Field Geology- Thank you for the unforgettable
memories and for making each day here a true
adventure. We love you Tom, Bucky, Erin, Cat,
Ryan, Virat, Sarah, Johanna, Katharine, and
Meredith. Webster Beach Bum