Ch.8 How Waves Move Sediments
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Ch.8 How Waves Move Sediments

Longshore. Drift. Longshore drift has a very powerful influence on the shape and composition of the coastline. It changes the slopes of beaches and creates long, narrow shoals of land called spits, that extend out from shore. .

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Ch.8 How Waves Move Sediments




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Ch.8 How Waves Move Sediments

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Longshore Drift

Longshore drift has a very powerful influence on the shape and composition of the coastline. It changes the slopes of beaches and creates long, narrow shoals of land called spits, that extend out from shore.

Longshore drift may also create or destroy entire

barrier islands

along a shoreline. 

A barrier island is a long offshore deposit of sand situated parallel to the coast.  As longshore drifts deposit, remove, and redeposit sand, barrier islands constantly change.

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NJ Coastal Zone

Monmouth County headlands consist of beaches backed by a bluff of older sediments and two major sand spits

One to the north from Long Branch (Sandy Hook)

One to the south from Bay Head (Mantoloking to Island Beach State Park)

The barrier island segmented shoreline covers the remainder of the NJ coastline where individual islands are separated from the mainland by a series of bays and tidal lagoons

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Ocean Currents

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Waves, Beaches, and Coasts

Water

waves are another agent of erosion, transportation, and deposition of sediment. Along the shores of oceans and lakes, waves break against the land, building it up in some places and tearing down in others.

The energy of the waves comes from the wind. This energy is used to a large extent in eroding and transporting sediment along the shoreline. Understanding how waves travel and move sediment can help you see how easily the balance of supply, transportation, and deposition of beach sediment can be disturbed. Such disturbances can be natural or human-made, and the changes that result often destroy beachfront homes and block harbors with sand.

Beaches have been called "rivers of sand" because breaking waves, as they sort and transport sediment, tend to move sand parallel to the shoreline. In this chapter we look at how beaches are formed and also examine the influence of wave action on such coastal features as sea cliffs, barrier islands, and terraces.

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Coastal Geomorphology

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Winter vs. Summer Profile (Fig. 8.3)

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Views of UCSB Beach at three different times of

year. The upper left is during the fall, when the sand is high. The upper right is after the first winter storm, and the figure to the left is in January. During this quarter, and while you are at UCSB, be sure to notice the effect of storms on our beach.

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Jetty or Groin?

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Longshore Drift

Tucker

s Island, New Jersey, is a barrier island that clearly illustrates how longshore drift and strong weather affect these transient sand deposits.

The island was first settled in 1735. Since its settlement, residents have had to move the island

s lighthouse several times because the channels shifted constantly as a result of longshore drift. Eventually, they placed the lighthouse on high ground at the island's northern end.

Meanwhile, the inlet north of Tucker

s Island—Beach Haven inlet—was also effected by longshore drift. At times, the inlet was narrow or nonexistent and Tucker

s Island was attached to the nearby Long Beach Island. At other times, the inlet was wide, and Tucker

s Island was separated from Long Beach Island.

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In 1927, the lighthouse on Tucker's Island, NJ was destroyed when powerful longshore currents washed over 300 yards of the surrounding land out to sea.

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Barnegat Light

Barnegat Light has seen significant advancement from 1986 to 2006 The Barnegat Inlet jetty was constructed between 1988 and 1991, and upon completion it began trapping sand

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Barnegat Light Cross Section

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Barnegat Inlet

Figure 7. Inlet channel conditions at Barnegat Inlet, New Jersey, August 1944.

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Ocean County

Shoreline

is open to free littoral sand transport

Narrow

beach width and extensive development limit dune development and storm protection

Large

advances around Barnegat inlet were due to jetty reconstruction

State

conducted large truck-fill in Harvey Cedars (1994 - 1995)

First

substantial Federally funded beach restoration project in Surf City, L.B.I (2007)

Undeveloped

area in Holgate lies down-drift from the 97-groin field along L.B.I and has been impacted by long-term shoreline change

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Sand Spit – Sandy Hook, NJ

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Figure 178. Maps showing the progressive shoreline changes at Sandy Hook (after NPS Spermaceti Cove Visitor Center display).

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Sandy Hook

Figure 179. Sedimentation features on aerial photographs of Sandy Hook: A. Plum Island represents the remnants of a

washover fan. The sawtooth pattern along the Atlantic Ocean side reveals the buildup of sand adjacent to stone groins transported northward by longshore drift. B. an accretionary sandy buildup on the northern tip of the spit. The large dark area is a newly-formed freshwater pond. The dotted straight line is the 9 Gun Batter completed in 1902.

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Rip Currents

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The Impact of Storms

HurricanesNor’Easters

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Sources

Surf Science

An Introduction to Waves for Surfing

by Tony Butt, Paul

Russel

, Rick

Grigg

Kurt

Korte

Surfline

NOAA

Surfline

Richard Stockton College of NJ

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