What are Consequences of Poorly Constructed Swales?

Erosion and Sedimentation

Poorly constructed swales can lead to erosion, particularly if they are not properly sloped or if the soil is not stabilized. A steep slope of 1:3 or greater can lead to rapid erosion, while a gentler slope of 1:6 or greater is typically recommended. Without adequate soil stabilization, the erosion can be exacerbated, leading to sedimentation downstream and potentially harming aquatic ecosystems.

Reduced Water Retention

A swale that is not properly sized or shaped can also reduce water retention, defeating the purpose of the water harvesting system. A general rule of thumb is to create a swale that is 1-2 times the size of the surrounding watershed, and to shape the swale with a gentle, S-curve to maximize water retention. Without proper sizing and shaping, the swale may not be able to hold enough water to make a meaningful impact on the surrounding landscape.

Flooding and Property Damage

In addition to erosion and reduced water retention, poorly constructed swales can also lead to flooding and property damage. If the swale is not properly integrated into the surrounding landscape, it can cause water to overflow and potentially harm nearby buildings or infrastructure. To avoid this, it’s essential to properly contour the surrounding landscape to ensure that the swale is able to absorb and retain rainwater without causing harm.