Erosion in Lakes & Ponds

Shorelines around many stormwater ponds are required to maintain slopes that are no steeper than four feet horizontal to one foot vertical. However, the natural erosion of these lake banks is inevitable, which can threaten compliance and the safety of community members.

Natural weather events, such as more frequent or more intense rainfall, can increase erosion, causing shorelines to crumble and deteriorate. Stronger storms, faster runoff velocity, and higher water levels also increase the levels of suspended sediment in waterbodies. This change in the distribution of sediment can threaten invertebrates, fish, and especially aquatic vegetation.

Unchecked increases in sediment and erosion in large lakes can also have a negative effect on water quality and the availability of drinking water sources. For instance, increased sedimentation can impact the storage capacity in reservoirs and increase the need for treatment by water utilities. These conditions require significant management efforts to reverse and prevent.

The topography of the land can contribute to lake soil erosion. In steeper areas, runoff moves at a higher intensity and increased speed. This means even heavier and larger sediment particles can easily be carried by the moving water. Because of this, hilly areas face more soil erosion problems. The longer and steeper the slope of a lake or pond bank, the higher the risk of erosion. As the slope length increases and aids the accumulation of runoff water, soil erosion also increases.

Tectonic activity molds the shape of the landscape itself, thus influencing how erosion affects an area. For example, tectonic uplift may cause one part of the landscape to become higher than other parts of the landscape. This process generally occurs over hundreds of years, but may also take place over the span of a few decades – enough for any long-term homeowner to watch their property change.

Human activity is a significant cause of lake soil erosion. When actions such as construction, logging, paving, farming, and even landscaping disturb the topsoil, they can increase the risk of erosion. Effects of human-caused soil erosion include:

• Level control structures – This can raise lake levels to an unnaturally high point on the shoreline where the soil is less able to withstand lake wave action.
  
• Stormwater runoff – When too much earth is paved over, these impervious surfaces around lakes collect and deliver precipitation over land rather than letting it infiltrate into the soil. This allows stormwater to pick up excess nutrients, trash, and other pollutants as it flows into the waterbody and create bad odors, algae, toxic cyanobacteria, nuisance aquatic plants, and bottom muck.
  
• Flooding – Lakes and ponds help contain water during rainstorms and weather events like hurricanes, but the more they fill with sediment, the less water they can hold. This is increasingly problematic as more of the land is paved over, preventing natural water filtration into the ground.

Homeowners often remove vegetation in order to create better views or gain access to the water. This destroys wildlife habitats and eliminates the shoreline stabilization provided by the root structures of plants, trees, and shrubs. Native plants help bind the soil together with their root systems, which means they’re able to serve as a protective layer that can help prevent erosion in several ways.

Plant cover protects the soil from the impact of heavy rains, which helps facilitate more effective soil absorption. In addition, firm plant placement impedes water flow as the stems create barriers that can uptake water. Once the protective vegetative cover is removed, land erosion occurs at a more destructive rate.

The effectiveness of plants for reducing erosion depends on the type and quantity of cover they provide. Native, flowering vegetation should completely cover the soil and grow in a thick, tall barrier 3-5 feet from the edge or a lake or pond. The appropriate plants can differ from state to state, so it’s important to confer with an aquatic specialist to identify the best species for your waterbody.