Ch.8 How Waves Move Sediments

Ch.8 How Waves Move Sediments

Longshore DriftLongshore 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.

NJ Coastal ZoneMonmouth 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

Ocean Currents

Waves, Beaches, and CoastsWater 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.

Coastal Geomorphology

Winter vs. Summer Profile (Fig. 8.3)

Views of UCSB Beach at three different times ofyear. 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.Jetty or Groin?

Longshore DriftTuckers 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 islands 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 Tuckers IslandBeach Haven inletwas also effected by longshore drift. At times, the inlet was narrow or nonexistent and Tuckers Island was attached to the nearby Long Beach Island. At other times, the inlet was wide, and Tuckers Island was separated from Long Beach Island.

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.

Barnegat LightBarnegat 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

Barnegat Light Cross Section

119ft shoreline advancement 121 yds/ft gain

17Barnegat Inlet

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

Sand Spit Sandy Hook, NJ

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

Rip Currents

The Impact of Storms HurricanesNorEasters

SourcesSurf Science An Introduction to Waves for Surfing by Tony Butt, Paul Russel, Rick GriggKurt Korte SurflineNOAASurflineRichard Stockton College of NJ