• Ryan O'Hanlon

What is erosion and why do I care?

Introduction

We hear the word erosion tossed around — but what is it? In a nutshell, erosion is when mechanical disruptions relocate loose soils. In our case, the disruption is usually flowing/moving water, including rain runoff and wave action. These soils are then often relocated to the bottom of a ditch, river, lake or pond. Erosion will create problems by reducing water volume capacity(depth), creating a system prone to nutrient loading issues and a failing shoreline, to name a few.


Water Quality

When we say water quality, it’s primarily the nutrient load or “how many nutrients are free floating within the water?”. When water bodies have excessive nutrients, algae blooms occur leading to unsightly views, reduced access and foul smells. But how does erosion cause this?


Let’s look at a new pond dug with a 10 feet original depth. At this point in a pond's life, most nutrient loading is from water inflow after rain events. Meaning, there is likely a low nutrient load and moderate to high water quality.


As the pond ages, water continues to flow in from rain and unpredictable storms bring unprecedented inflow. While this goes on, eroded soils are being quietly relocated into the pond and stored at the bottom. The pond has not only reduced it’s volume, restricting its use/access, these relocated soils are holding nutrients like a sponge. The relocated soils, now referred to as sediment, are releasing nutrients continually. This decreases overall water quality by applying an extremely large amount of nutrients to the water body.



Shoreline Stability and Safety

The shoreline is susceptible to erosion from rain inflow, wave action and in some cases general use from boat entry, vehicle use etc. In the event of rain inflow we have a case as discussed above, where soils are relocated to the bottom of the pond over time.


Wave action, caused by high winds or boats, creates a different safety concern. The shoreline begins to form an undercut. Let’s reference our new pond scenario again. As the pond ages, wind and boats create wave action that frequently beat on the shoreline creating undercut sections which cannot not always support the weight of a person. This means someone can fall into the pond or lake. Furthermore, additional soil has been relocated and added more sediment to the pond.



How do I prevent this?

Erosion is inevitable and will occur to some degree, we can however reduce it. Securing the shoreline is a great start. Seeding and planting around the pond early provides plants the opportunity to hold on to soils before they can be relocated to the pond. This works best when plants are around the pond, along the water's edge and in the shallows/littoral zone.


Poor pond design can lead to erosion issues, so be sure that those digging and designing know what they’re doing! Mechanically securing the shoreline has also been used in the past via plant carpets and woven concrete mats. Pre-grown plant carpets are ‘rolled out’ like a carpet to provide near instant shoreline protection. These can also be used as part of a shoreline erosion repair.