Erosion on the Great Lakes

By: Samantha Lee

The Coast of the Great Lakes

• Can be in the form of a low laying coastal marsh (which is subject to flooding)

• Can also be in the form of high rock cliffs (basically non-erodible)

• It is made of till, which is erodible, glacially deposited sand, gravel, clay, and a clay-like material

~Erosion~Is the wearing away of land by the action of natural forces but

can be influenced, both adversely and beneficially, by

human activity.

Forces of Erosion

• Waves• Currents• Wind• Surface Water Flow• Ground Water Flow• Freeze-thaw Cycles

• Coastal Geomorphology

• Meteorology and Waves

• Lake Levels• Littoral Transport and

Sand Supply• Erosion and

Recession• Lake Levels and

Erosion

Forces of Erosion cont...

All these forces are usually not present at any certain location. Even though erosion is an all

natural process, human activity has a large effect on erosion (can

be either good or bad).

http://www.lre.usace.army.mil/Photos/index.cfm?pge_prg_id=10487&pge_id=1197&id=3576

This is a picture of the Great Lakes coast after structural damage occurred

GeomorphologyGeomorphology is the overall shape and form of earth’s surface and

changes that occur within it.The Coastal Geomorphology of the Great Lakes comes from a glacial

origin and there are a variety of general shore types in the region of the Great Lakes such as:

~ Rocky Bluffs (high and low)~ Low Flood Plains~ Coastal Marshes~ Sand/Till Bluffs (high and low)~Sand Dunes~Artificial Coastlines

These shore types are formed from materials that were deposited over ten thousand years ago by glaciers

Coastal Geomorphology cont…

This picture shows the view of a typical beach profile. The process of erosion occurs from the water depth of about 30ft to the shore.

Meteorology and Waves

Waves which are created by wind, are the primary agent of erosion. Energy is

determined by meteorological, topographic, and hydrographic factors

(distance of blown wind and the depth of water where wind is generated). The depth of water in the Great Lakes can support the largest generated waves

possible, and more.

Lake LevelsThe primary factors that have an affect on

water level fluctuations are:

• Precipitation• Runoff• Evaporation• Meteorological

Disturbances• Crustal Movement

• Groundwater• Ice Formation• Aquatic Plant Growth• Human Activity

(diversion of lake water, consumption, urbanization, and coastline development)

Littoral Transport and

Sand SupplyLittoral Transport is when the waves and currents move materials (sand,

gravel, silt-sized particles, and rocks) on the coastline

Over periods of time, erosion can occur followed by a build-up of sand (also called accretion). Over a long period of time, the area would be in a “dynamic equilibrium” state. A large reduction in the sand supply of an area creates a gap in the sand budget, which can only be balanced by increased erosion

Humans may Benefit the Sand Supply

Where many of the large harbors are located around the Great Lakes, the reduction in sand supply effected by the large navigation structures on the coast, has been toned down by harbor’s beach nourishment programs and sand bypassing. These programs maintain a balance in the sand supply by reintroducing sand into the littoral transport system which has been blocked by the navigation structures.

Shore Protection Structures

The purpose of all shore protection structures are to reduce wave energy. This can be either by acting as a barrier to wave energy (seawalls and revetments), or indirectly by absorbing wave energy through the building of artificial beaches (groins).

Erosion and Recession• Erosion is defined as the

wearing away of land. It is expressed as a change in volume.

• Recession is the landward movement of a feature. It is expressed as a change in distance. Also, a consequence of erosion.

Lake Levels and Erosion

In the Great Lakes, lake level has no significant effect on erosion. This is because variation in lake levels have little effect on the primary erosion agent, waves. They do have an effect on where wave energy is dissipated on the beach profile, which can affect bluff recession rates over short periods of time. But, as long as the other factors that determine wave energy remain the same, the erosion rate would remain basically unchanged over long periods of time.

http://www.Ire.usace.army.mil/greatlakes/hh/coastalprocesses/coastaltopics/

Shown here is a sediment budget. This makes it easier to understand how much material is entering and leaving the area, and how much of it is being lost in deeper water.

References

• http://www.Ire.usace.army.mil/greatlakes/hh/coastalprocesses/coastaltopics/

• http://www.Ire.usace.army.mil/greatlakes/hh/coastalprocesses/greatlakeserosionfactsheet/

• http://www.Ire.usace.army.mil/greatlakes/hh/coastalprocesses/glossary