Our Powerboats & Shoreline Erosion

EDITORS NOTE: This article is third in a seven-part series that will help readers understand the impact of motorized boats on Lake Beulah. Most information comes from the Wisconsin Department of Natural Resources (PUBL-SS-948-00)

Erosion on Lake Beulah’s shores has been a fact of life since the lake was formed. It wouldn’t be such a big deal if it weren’t for all the man-made structures put up over the years. The focus of this article is on the impact of power boats, but readers might be interested to know parts of the lake oftentimes experience serious shoreline erosion via ice damage.

Early lake property owners protected their shorelines with logs or long planks. Some had concrete seawalls constructed. Today, seawalls already installed are grandfathered, but otherwise no longer permitted.

Ride around the lake and you’ll see many properties with large boulders lining the shoreline. These must be granite, or some otherwise impermeable rock because if water can get in, the rock will freeze and break into smaller and smaller bits over the years.

Back to the subject at hand, erosion refers to particles of solid material on the shoreline which becomes detached and transported by currents and wave energy. Erosion is important because it may affect water clarity, shade aquatic plants and provide nutrients for unwanted growth of algae. It can also negatively impact fish and wildlife dependent on near-shore habitat. Erosion can also impact property values and it can be expensive to control.

Boat waves impact shoreline erosion. Logically, the larger the wave, the greater the impact. Turbulence created by boats can also impact shoreline erosion by destabilizing the lake bottom. While the frequency of waves pounding the shore can be inferred to make a difference in erosion, little is known about this variable.

Wave size increases with both length and depth of boat draft. Boat operating distance from shore is associated with smaller waves as are faster speeds. These factors are why wake boats on the lake are running deep in the water and at slow speeds. This gives them the ability to create extremely large waves.

The number of boats operating on the lake at the same time also makes a difference. Studies show that individual boat waves dissipate more quickly than when boats operate in traffic with other boats, in which case they can create much bigger waves that persist for longer periods of time. In other words, the more big waves, the bigger the waves.

Recent research data from the University of Minnesota shows that waves from wake boats must be at least 500 feet from the shoreline/docks and other boats (or the distance of a little less than 1.5 football fields) to decrease their wake wave characteristics to levels similar to non-wake surf boats. To read the full research study entitled, “A Field Study of Maximum Wave Height, Total Wave Energy, and Maximum Wave Power Produced by Four Recreational Boats on a Freshwater Lake,” visit the University Digital Conservancy website.

Seems hard to believe, but not that long ago the boats with biggest waves were runabouts. In 2024, on Lake Beulah, there is an undisputed new king of wave height.