Understanding lakeshore ecosystems — Part 4: Shoreline erosion
The easiest way to look for erosion and its possible causes is to walk along the shoreline or take a boat ride close to the shoreline.
A helpful resource for identifying and reducing shoreline erosion for property owners is “Understanding, Living With, and Controlling Shoreline Erosion a Guidebook for Shoreline Property Owners” by the Watershed Council. However, the easiest way to spot erosion and its possible causes is to walk along the shoreline or take a boat ride close to the shoreline. When looking for erosion, you will be able to identify if the erosion is naturally caused, human caused, site-specific (only on your property) or widespread.
Some possible causes of erosion:
- Overland runoff. This is water that flows over the ground instead of soaking into the ground. Runoff is a result of natural and human activities. Runoff carries soil particles and other pollutants, such as fertilizers, pet wastes, oil, etc. into the lake. This runoff may originate a long distance from the lake.
- Groundwater seepage and springs. Ground water seepage is a natural condition where the water table meets the land surface. These areas have characteristics of a wet spot, a wet layer in a steep bank or a flow of water.
- Removing vegetation. Erosion problems simply occur due to removing shoreline vegetation. The roots of plants hold the shoreline in place.
- Waves. Natural or man-made waves are the most common cause of shoreline erosion. Property on the windward side of the lake has the greatest impact.
- Ice action. As temperatures rise in the spring, ice is pushed up onto the shoreline; this impacts the bank and causes it to move back, creating an ice ridge. Ice ridges actually protect the shoreline from further ice damage and should not be removed.
Here is a quick list of the most noticeable signs of trouble:
- Large areas of bare soil along the shore, especially on a steep bank.
- Large or small gullies by overland runoff along the shoreline.
- Frequent landslides or excessive bank slumping.
- Noticeable recession of the shoreline over a period of time.
- Leaning or downed trees with exposed roots on the shoreline.
- Large patches of unusually cloudy (turbid) water near a lakeshore, especially during periods of high water.
Wave and ice erosion is hard to predict. Ice damage changes from year to year. The size of waves are largely dependent on two factors: wind speed and lake fetch. Fetch is the distance the wind can travel over water before meeting the land.
There is an online Erosion Calculator the can be used to find what the wave energy is at a particular site. To use the calculator, you need to use a lake map that shows the topography of the bottom of the lake. Many Michigan inland lake topography maps are available on the Michigan Department of Natural Resources site.
Wave energy should be calculated before any shoreline erosion control project begins. This will give you information on the how to select the best erosion control method for your particular project.
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