FS-020 (pg. 1 of 3)
OHIO SEA GRANT AND STONE LABORATORY
Beaches Are
Shore Protection
Wave erosion during Super Storm Sandy
on October 30, 2012.
(Left) Large waves are reaching the shore
and breaking against shore erosion
devices and smaller waves breaking
on the sloping beach at Fairport Harbor
Beach looking east towards Painesville
Township Park, Lake County, Ohio.
(Above) Just east of Painesville Township
Park, Lake County, Ohio, the waves are
reaching the base of the bluffs.
Frank R. Lichtkoppler
Extension Program
Coordinator
[email protected]
Ohio Sea Grant
1314 Kinnear Road
Area 100
Columbus, OH 43212
614-292-8949
ohioseagrant.osu.edu
A
lmost everyone recognizes the value of a beach for recreational purposes. But how many people
know that a beach is one of the best natural shore protection features a shoreline property owner
can have? Beaches are, in fact, part of the first line of defense against excessive shore erosion.
Beaches are temporary geologic features found where land and water meet. They are composed of a
collection of rock or shell fragments, ranging in size from fine sand to large boulders. For Lake Erie, zebra
and quagga mussel shells can be important particles on a beach. Because this accumulation can be moved
by ordinary wave action, beaches are always in motion! Movement of beach material may be parallel to land,
away from land, or toward land.
Berms and bars are important features of the coastline (Figure 1). The flat, above-water section between
a bluff and the water is called the berm. It is the part of the beach we usually walk on. Sometimes offshore
and under water, there are ridges of sand that roughly parallel the shore. These ridges are called bars. The
presence of these two features affects a beach’s ability to dissipate wave energy and protect against erosion.
FIGURE 1. An idealized beach.
Ohio Sea Grant, based at The
Ohio State University, is one
of 33 state programs in the
National Sea Grant College
Program of the National
Oceanic and Atmospheric
Administration (NOAA),
Department of Commerce.
Ohio Sea Grant is supported
by the Ohio Board of Regents,
Ohio State University
Extension, other universities,
industries, and associations.
OHSU-FS-020
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FS-020 (pg. 2 of 3)
Beaches Are Shore Protection | 2014 Ohio Sea Grant and Stone Laboratory
The narrow beach at Arcola Creek in eastern Lake County, Ohio. Note that the
beach consists of relatively large size pebbles and cobble denoting a beach
exposed to a relatively high energy wave attack.
Waves generated by wind are responsible for shoreline erosion
(see Ohio Sea Grant Fact Sheet 019, Lake Erie Shore Erosion).
The amount of energy in and the physical characteristics of
a wave are dependent on the speed of the wind, the wind’s
duration, and the fetch – the unobstructed distance the wind
blows over the water. Generally, the greater the speed and
duration of the wind, the larger the wave that is generated; and
the longer the fetch, the longer the spacing between wave crests.
Large waves contain more energy and thus have a greater ability
to erode shoreline materials than smaller waves. Steep nearshore
bottom slopes allow large waves to break on the beach with
greater force than do shallow nearshore bottom slopes.
The berm, bars and steepness of the lake bottom near the
shore can all affect the height of an incoming wave, but their
presence can also affect erosion rates. Large waves will break
on a nearshore bar or in shallow water and lose a great amount
of energy before reaching the shore. Waves that reach the
shore unimpeded will break on the berm of the beach and
dissipate their energy before reaching the base of the bluff. But
a narrow berm, a steep nearshore slope and a lack of bars will
allow large waves to break directly against the base of the bluff,
resulting in a greatly increased rate of bluff erosion. A welldeveloped beach with a wide berm, a shallow nearshore slope,
and nearshore bars will protect the shoreline by absorbing and
dissipating wave energy.
Where does the material to form a beach come from? The
primary source of sand and gravel for beaches in northeast
Ohio comes from the erosion of shoreline bluffs. Approximately
20 percent of the material eroded from Ohio bluffs is sand and
gravel, which is available for beach building. The remainder is
fine silt and clay, which is carried out into the deeper portions
of the lake. In recent decades, zebra and quagga mussel shells,
washed onto the beach by large waves, have become important
materials on some Lake Erie beaches as well. Rivers draining
into Lake Erie also carry substantial amounts of fine silt and clay,
but very little sand. However, even this small amount of sand
from the river does help to build beaches.
LITTORAL TRANSPORT
Littoral transport is the movement of material in the nearshore
zone by waves and currents. Littoral drift is the material that
is being moved. This movement may be parallel to the shore,
onshore or offshore. Littoral transport is the mechanism that
moves particles on beaches.
Dr. Willard Bascom refers to the littoral transport mechanism
as the “littoral conveyor belt” in his book Waves and Beaches
(1980), because it picks up material in one spot and moves it
down the shoreline.
In some cases, man-made structures may impede the natural
flow of material. Thus the littoral transport mechanism may
remove material from where we would like to have it – on the
beach – and place it where we do not want it - in the harbor
channel entrance.
Waves and the currents they generate are the primary agents
of littoral transport – their energy picks up the sand and moves
it along the beach. Breaking waves carry sand onshore and
offshore in short steps. Most waves strike the shore at an
angle, which moves the sand on the beach in a series of zigzag
patterns as successive waves strike the shoreline (Figure 2).
The overall effect of this wash-and-swash action is to set up a
current along the shoreline. The term downdrift refers to the
predominant direction of the littoral transport.
FIGURE 2. Zig-zag movement of sand responding to runup and return waves.
FS-020 (pg. 3 of 3)
Beaches Are Shore Protection | 2014 Ohio Sea Grant and Stone Laboratory
Taken during Super Storm Sandy on October 30, 2012 at Mentor Beach Park in
Mentor-on-the-Lake, Ohio. Note there is no beach and the waves are breaking
directly on the revetment at the base of the bluff.
The broad beach at Conneaut Township Park consists of fine sands and is held in
place by the large harbor breakwaters constructed to aid commercial navigation.
Wave energy will be dissipated on the beach typically moving material from the left
to the right in the photo above.
The general direction of littoral transport in northeast Ohio
(east of Avon Point) is from west to east, because most waves
are generated by winds coming from the southwest. Storms
from the northeast can and do move large amounts of material
from east to west, but over the long term more material is
carried to the east by the more constant southwesterly waves.
The amount of material and distance it is moved in a single
day is highly variable. Most movement occurs slightly offshore
and goes unnoticed, and often shore property owners notice
changes in their beach only after large storms, over a long
period of time, or during a period of high lake water levels.
To determine the direction of the littoral transport system
along a specific beach, look at a groin oriented perpendicular
to the shore. Sand will accumulate on the up-drift side of the
structure – the side facing into the nearshore current - and it
is removed from or deficient on the downdrift side (Figure 3).
An understanding of the importance of beaches as natural
shore protection and the littoral transport process is basic to
understanding the Lake Erie shoreline erosion problem. This
understanding, in turn, can help coastal property owners avoid
costly mistakes in protecting their property.
Many shoreline property owners are faced with erosion
problems and must make decisions about them. Any attempt
to slow down and lessen the effects of this natural process
requires time, money, and effort and can just move the erosion
problem downdrift to adjacent properties. Thus it is particularly
important for the coastal property owner to learn and
understand as much about shore erosion as possible. A good
place to start is the ODNR–Office of Coastal Management web
site at: http://www.dnr.state.oh.us/coastal.
FOR MORE INFORMATION ON EROSION, CONTACT:
ODNR Office of
Ohio Sea Grant Extension
Coastal Management
1314 Kinnear Rd.
105 West Shoreline Drive
Columbus, OH 43212
Sandusky OH 44870
614-292-8949
419-626-7980
ohioseagrant.osu.edu
1-888-OHIO-CMP (toll free)
[email protected]
coastal.ohiodnr.gov
References
FIGURE 3. Idealized effect of a groin on the longshore transport
of sand.
Bascom, Willard. 1980. Waves and Beaches. New York, New York: Anchor Books
366 pp.
Carter, Charles H. Lake Erie Shore Erosion 1976, Lake County, Ohio : Setting,
Processes and Recession Rates from 1973 to 1976. Report of investigations
No.99, Ohio Geological Survey, Ohio Department of Natural Resources. 105 pp.
Carter, Charles H., Donald E. Guy, Jr. and Jonathan A. Fuller. 1981. Coastal
Geomorphology and the Geology of the Ohio Shore of Lake Erie. Geological
Soc. American, Cincinnati Field Trip Guidebook, American Geological institute,
Vol. 3 pp. 433-456.
Carter, Charles H., William J. Neil, William S. Haras, and Orrin H. Pilkey, Jr. 1987.
Living with the Lake Erie Shore. Duke University Press. Durham, North Carolina.
263 pp.