Swales should have side slopes no steeper than what ratio?

The recommended side slope ratio for swales is 3:1, which means for every three units of horizontal distance, there should be one unit of vertical rise. This ratio is generally deemed appropriate to ensure stability and prevent erosion of the swale sides.

A steeper slope, such as a 2:1 ratio, may pose risks of soil slippage and not provide the necessary vegetation coverage to control water flow efficiently. Conversely, a gentler slope like 4:1 or 5:1 might not effectively convey water as intended, reducing the functionality of the swale. The 3:1 ratio strikes a balance between maintenance of soil integrity and effective water management, aligning with best practices in erosion and sediment control.