Geomorphic Engineering

Wave Erosion

Wave Protection

Slumping

Home

Coastal shorelines erode due to various processes.  Waves are usually the erosion factor that lead to the most extreme and rapid changes.  Storms waves usually cause the most erosion.  The eroded material is carried offshore.  During periods of low-energy waves, material is carried shoreward.  Since storms are typically seasonal, it can be expected that more shoreline erosion will happen during certain times of the year.  Along the stretch of the Lake Superior shoreline that our class visited, November (late fall/early winter) was the big storm season. 

There are four major erosional processes that function along coasts: 
                Corrosion- Solution of coastal rocks by chemical action of seawater
                Attrition- Diminution of rock particles as water rolls, bounces, or slides them on a
                     beach or wave-cut platform
                Corrasion- Physical erosion of bedrock caused by the grinding action of rock
                     fragments that are carried in the ocean waves and currents
                Hydraulic action- Erosion caused by the force of the water itself.  This includes
                     wave shock pressure and pneumatic

There are four major types of breaking waves: 
               Spilling- The top of the wave crest becomes unstable first and flows down the wave
                    front as an irregular foam.
               Plunging- The wave crest curls over the front face and falls with a splashing action
                    into the base of the wave
               Surging- The wave crest remains essentially unbroken, but the base of the wave
                     front advances up the beach.
               Collapsing- Its characteristics are between those of the plunging and the surging
                    types.

 
Figure adapted from Ritter et. al. 2002

Most breaking waves aren’t erosional, in fact, they tend to push sediment towards the shore.  Plunging waves however, are erosive.  They will carry sediment away from the shore.  

The shore down by the water is covered in rounded rocks. It was obvious that the shoreline was old.

Ritter, D.F., Kochel, R.C., Miller, J.R., 2002, Process geomorphology: New York, McGraw-
            Hill Company, 560 p.

By Amy Wichlacz

Top