How Erosion Starts & Progresses
Most stormwater ponds were designed & constructed with a 4:1 shoreline slope. This protects residents & landscape crews from falling into the lake. Engineers used to think this would also prevent erosion. They were wrong.
The water level changes between rainy summer & dry winter seasons. How much it varies depends on many factors, but mostly on soil seepage & evaporation.
This changing water level allows the shore to erode at two or more levels each year.
Most erosion is caused by little two-inch-tall waves washing against the shore. The wind forms the waves, so the location of erosion depends on the direction of the wind. In southwest Florida, wind direction often changes between morning & afternoon, causing erosion on both sides of the lake.
The waves are how erosion starts on most stormwater ponds. There are several mechanisms or processes that cause this erosion. The main factor is that sandy soil easily washes away.
The yellow line indicates the original shoreline. This image illustrates the water level during the dry season. During the wet summer & fall, the water level would be closer to the grass line. The erosion caused the “step-down” along the edge of the grass.
You can also notice on this drawing that the drop-off location is a mini overhanging cliff. This angle is common. The turf right at the edge becomes unstable & dangerous because it collapses easily.
Heavy mowers traveling next to the lake vibrate the soil & shake the sandy soil loose. This happens every week.
This area is a dangerous location for mowing staff. Wet grass from morning dew is slippery. Heavy mowers can fall into the lake, turn over & pin the driver under the water. Fortunately, most mowing staff are young men who have excellent reaction times & rarely get hurt.
View any of our other articles about erosion or call Beautiful Ponds for more information on how to stop erosion in your lake.