In site drainage terms, what exactly is a swale?

A swale is deliberately simple: a shallow, broad depression shaped into the ground so that surface water collects in it and follows it to somewhere harmless. It is a surface feature, which is what distinguishes it from every buried alternative, and its advantages follow from that — it cannot clog the way a pipe can, its condition is visible, and maintaining it means mowing and occasionally reshaping rather than excavating. Swales are the standard answer where a site sheds water toward a building or where a neighbouring property drains across the lot, because they intercept the flow high and redirect it around rather than trying to fight it at the foundation. Inspectors report whether a swale is present where the grade calls for one, and whether an existing swale has silted in or been filled by landscaping, which is how they most often fail.

A swale is a shallow surface channel graded to collect runoff and direct it around a structure. Being at the surface, it cannot clog like a buried pipe and its condition can be seen and maintained.

Site drainage uses surface features and subsurface systems. A swale is a graded surface channel that intercepts and redirects runoff; French drains, footing drains and storm laterals handle water below grade. Swales commonly fail by silting in or being filled during landscaping.

A Swale Is a Shape, Not a Pipe. You mow it, you can see it, and it cannot clog. Everything buried is something else.

Check whether an existing swale still holds its shape. Silted, filled or planted swales are extremely common and look like ordinary lawn until it rains.

• •Confusing a swale with a French drain or footing drain
• •Assuming a swale exists because the grade suggests one should
• •Missing a swale that has been filled in by landscaping