Josh is our contractor; we rented a Bobcat E-35 mini-excavator, and (after the appropriate line locates, to determine where all the many different kinds of “lines” for infrastructure were), Josh got to work, digging for the Swale.
The Swale is a “dry stream” bed. The reason one builds a swale is to capture rain water and release it gradually to the ground. Swales in nature do much the same thing, having capacity to hold large amounts of water, and allowing the water to slowly seep into the surrounding soil.
In some cities in Europe, people are not allowed to let water run off their properties (within reason – sometimes, one has no choice with a flash flood), and this has led to people using swales as common features in their landscaping. Josh has a swale at his home.
The swale has been designed to run from the highest point of the garden to the lowest. It is almost entirely flat, in three sections, giving the water time to seep into the soil. If there is a lot of rain, the water will flow out of one nearly flat section, over a little waterfall, to the next, and so on. However, the swale should have the capacity to hold a lot of water, without overflow from the lowest pond.
Although Swales will not necessarily hold ALL the water from a significant rain event, this is what they are best at! They will hold a lot of that water, thus diminishing the effect on urban infrastructure, as well as the effect on the environment. If water runs off my front lawn, onto the street, into the storm sewers and then into the river, it picks up pollutants along the way, washing chemicals into the river to kill the life that grows there. Thus, there are three good reasons for building swales in your yards: to ensure you don’t have to water your garden as much (because the water goes into the ground), to save the city’s infrastructure (which was not built for the number of rain events we have been having), and to keep our rivers healthy. Plus, they are fun to play in and good looking as well.