The stream below my house, at the bottom of our yard is part of Beaver Run, a stream that originates about a mile west of us, near the top of our watershed. I love spending time in this stream, especially with my toddler, splashing around, watching minnows and cooling off in the always cold water. Although beautifully lined by woods, the banks of this section of Beaver Run are heavily eroded with banks of bare soil at each bend. While for many, this has become a common site in our watersheds, it is a relatively new phenomenon, one that coincides with the emergence of industrial agriculture and urban expansion.
A precolonial Beaver Run would have looked very different than the one in my backyard today. It likely would have had gently sloped banks on either side that acted as floodplains during heavy rains and spread out in multiple different meanderings. And as the name suggests it likely had multiple beaver dams along its length that slowed and spread the flowing water and created ponds filled with ecologic abundance. I have yet to see a beaver in Beaver Run!
So how did this gently meandering run of streams, ponds and wetlands become the narrow and eroded stream that we have today?
Much of the rain water that once soaked into the soils of our regions forests and savannas now runs off into storm water systems of sewers, drains and ditches and enters the streams and rivers of our Chesapeake Bay watershed.Our modern landscapes of industrial farms and urban hardscapes are designed to shed water away from fields and foundations. Not only is this water no longer available to be utilized by plants and to charge underground springs, it also carries with it anything it picks up along the way such as fertilizers, pesticides and soil, to name a few.
This increase in storm water has been compounded by the trapping of beavers during the fur trade that led to the near extinction of this once abundant ecosystem engineer and has accelerated stream channel erosion.
There certainly are reasons for wanting to get water away from our inhabited spaces. Any one with a wet basement knows the damage that water in the wrong place can do! We do not, however, have to choose between saturating our foundations and infiltrating storm water, it is only a matter of getting the water to where we want it.
This is where swales and rain gardens come in!
Swales and Rain Gardens: A Brief Overview
Swales and rain gardens are both techniques to slow and infiltrate water. They are low-tech solutions that are easy to implement in our front and backyards and can collectively make a big difference for our watersheds. When we infiltrate storm water into soil we make it available to plant roots and recharge aquifers and springs which gently enter streams and rivers. And we reduce flooding in our yards and neighborhoods.
Rain gardens are used to infiltrate large amounts of storm water in a small area. Swales, on the other hand, are used to spread water out over longer distances to more evenly hydrate the landscape.
Rain gardens are basins that catch water from downspouts or hard surfaces and allow the water to infiltrate. This is done by making a basin in the ground where water can pool. On sloped ground, a berm can be used on the down slope of the basin to hold water. In my area, heavy clay soils are the norm, so often the soil of a rain garden is dug out and replaced with a sand and compost mix that serves this purpose better.
Photo Left: An excavated, yet to be filled rain garden holding storm water from a rain event.
Unlike a pond that is intended to hold and store water, rain gardens are only meant to hold water for a few hours up to a day while the water soaks into the landscape.
Rain gardens are often planted to native flowers and grasses to provide additional benefits to local ecology. They are easy to install on small scale with small equipment or by hand and fit nicely into most urban and suburban yards.
Photo Right: Finished rain garden, filled with sand/compost mix and planted with native wildflowers
A Swale is like a long skinny rain garden, along the contour of the land. They consist of a ditch on the upslope and a berm on the downslope that, when constructed on contour, catch and infiltrate water. Think of a raised garden bed in which the bed is the berm of the swale and the path is the ditch. The whole length of the path is level with itself.
Photo Left: A newly dug swale, filled from a heavy rain event
Swales are useful when intercepting sheet flow over a larger area that a rain garden could not catch. They are also a useful way of spreading water from a concentrated source like a downspout across the contour of a yard. In this way a swale can make use of storm water to hydrate a larger area than a rain garden can. The berm of the swale is a great place to plant perrenial polycultures of fruit trees/shrubs and herbs.
Photo Right: The berm of this swale has been planted to an edible and medicinal perrenial polyculture.
Swales and rain gardens can also be combined and blended to soak and move water in creative ways!
So, do your yard and watershed a favor and consider catching your storm water runoff with swales and rain gardens!
Sources and Further Reading
Montgomery County Rain Garden Manual
Article: Buried leaves reveal precolonial eastern forests and guide stream restoration
Article: Leave It to Beavers: Keystone Species Provides Nature-based Restoration
Water Stories