Mechanical control of cattails usually involves a combination of Rodeo application or cutting the plants and submerging them below the water surface. This actually suffocates the roots or the plants. Both of these methods are short term solutions and actually cost more money than installing the right plants from the outset. In this sense, a swale is a ditch or drainage channel. These swales are common and necessary to drain runoff above ground.
Common examples are along roadsides or leading into retention basins.
These areas may not have the same needs as a larger retention basin, however, they are a source of difficulty in maintenance. The steep sides if mowed too closely can erode.