Dune Erosion 101

Michigan is home to the world’s largest collection of freshwater sand dunes, and they attract thousands of visitors each year.  The stunning beauty of these “living dunes” comes in part from their ever-changing nature as winds and water continually add, shift, and remove sand.  The daily changes are part of the delight of living along Lake Michigan, but the tension between a dynamic dune and static human structures is a unique challenge for lakeshore property owners.

Dune & Erosion Basics

Dunes are hills on the move.  Unlike hills made of soil or rock, dunes naturally move over time -- often slowly, but sometimes very quickly as they are subjected to wind and water.  Along the Great Lakes, cyclical changes in water levels and storm waves move tremendous amounts of sand both onshore and offshore.   Human overuse of dunes can accelerate erosion, which hurts both property values and dune ecology.  To best protect their Lake Michigan dune property, owners should understand the basics of dune dynamics. 

• All dunes move.  Shoreline dunes, which are so appealing for human and animal use, are especially subject to natural forces of change and can move far more rapidly than inland dunes.  This point cannot be emphasized enough.

• Natural processes. Cyclical wind and wave processes normally maintain a relative balance between sand deposition and removal. Sometimes, very high water levels and storm waves can eliminate beaches and damage the base (or “toe”) of lakefront dunes, as happened along Lake Michigan in the mid-1980s and again in 2019-2020.  Over subsequent years, dunes will gradually re-build through wind and water deposition of sand.

• Resting slope.  Normally, dry beach sand is happy to rest on a slope from 0-35 degrees.  If high water or waves, human construction, or other forces increase the slope's angle to higher than 35 degrees, sand will slide down (erode) so the dune can resume its natural resting angle*.  This erosion can damage or destroy human infrastructures like stairs, drainage fields, decks, and even homes.  

• Clay layers. Some southwest Michigan dunes, especially near Coloma and from South Haven to Fennville, have deep layers or "lenses" of clay that complicate normal dune dynamics. These layers force rainwater to flow laterally through the dune (instead of percolating down through the sand to join the water table).  This water emerges mid-dune and flows down the dune's face (called "weeping") which can cause sudden landslides (called sloughing or slumping; more info here).  This movement of water and sand/clay (especially during spring when the frozen water thaws) damages or removes vegetation that helps stabilize the dune.  

High dunes and dunes with clay layers tend to show occassional but sudden "slumps" that can threaten dune-top trees and human structures (adapted from Edil, 2010).

Protecting Your Property from Dune Changes: Planning & Planting

(1) Planning:  Owners must carefully consider the placement and the ongoing protection of manmade structures on their lakeshore dunes.  Important questions include these: 

• How will normal cycles of water and wind affect my dune’s unique slope and stability?   How will 50-year or even 100-year record water levels affect the dune’s slope and stability?  (The Army Corp of Engineers has historic Great Lakes water level data here.) 

• How will both natural and manmade changes to the dune (e.g., removal of trees, installation of a drainage field) change the likelihood of erosion?

• Where and how should structures be placed on the property to enhance lakeside enjoyment without creating a future erosion hazard (e.g., paths vs. elevated walkways, drainage fields)?  What is the best way to secure structures in order to compensate for expected dune movement and erosion? 

In summary, understanding the dynamic nature of dunes can help lakeshore owners carefully plan the development and protection of their property against erosion threats.  Another preventative step is understanding the importance of native dune vegetation. 

(2) Planting: Beaches and the “toe” of lakeshore dunes experience frequent assaults by wind and water; as a result, few plants or animals live in these areas.  Further away from the beach, native grasses grow a rich network of roots that stabilize the sand and respond to wind-borne sand accumulation around their stems by rapidly growing taller.  Once the grasses become established, a predictable succession of plants begin to thrive (e.g., milkweed, grapevine), followed by shrubs (e.g., sand cherries, junipers) and trees (e.g., pine, oak, cottonwood).  The progression and growth cycles of native vegetation do more than stabilize the dune: they naturally enhance the soil and provide food and shelter for a rich diversity of mammals, birds, insects, and reptiles.   Non-native plants, such as English ivy, vinca (periwinkle), and pachysandra, do help stabilize the dune but do not provide the benefits of native plants.

 Significant removal of native vegetation (to build a home, create a yard, or build stairs to the beach) increases the threat of erosion even on a mature dune.  Understanding the importance of native dune vegetation is a critical part of property protection. 

Dune environments show predictable patterns of vegetation growth (graphic from www.nature.com/scitable/knowledge/library/succession-a-closer-look-13256638/)

Options for Responding to Erosion 

Lakeshore property owners have several options for responding to erosion threats, but all of them have financial and environmental costs. 

“Wait and see” approach.   Here, the owner does nothing to interfere with natural erosion processes.  This is a reasonable strategy if the property is vacant or if structures are far from the crest of the dune.  However, if structures are near the lakeshore or near eroding areas, this strategy risks significant damage to or even loss of property.  

“Soft” or semi-permanent barriers:  Here, the owner installs a short-term barrier (3-5 years) at the base of the dune to reduce waves erosion and to enhance windborne sand deposition.  This approach includes installing sand fencing or geotextile bags, both of which can be removed as the dune naturally recovers.  If installed early in the erosion process, this is an effective and relatively inexpensive approach that stabilizes the dune and protects structures while the dune rebuilds itself.  Another advantage of this approach is that "soft" structures do not introduce long-term aesthetic or environmental problems.

“Hard” or permanent barriers: Here, the owner installs a long-lasting barrier to prevent waves from reaching the dune's base.  These "revetments" or “coastal armoring" may be impermeable (e.g., vertical walls made of cement, steel or wood) or semi-permeable (e.g., piles of large rocks).  This approach is often effective at protecting property in the short- and medium-term (10-40 years), but they have some drawbacks. They are very expensive, require lengthy permit processes, pose safety issues for people and animals trying to access the water, appear unattractive or unnatural to beach walkers/visitors, and can actually increase beach erosion dune to wave reflection and wave scouring).  Some Lake Michigan municipalities limit or prohibit the use of hard barriers. 

DRS offers free consultations in which we assess the property's geographic and structural features and advise owners about ways to manage their lakeshore property.  By working closely together, we hope many generations can safely enjoy this unique landform.