That’s right folks! With very little skill you can build a system in your yard that will help purify streams and lakes. It will prevent many toxins from entering the waterways and improve water tables. But that’s not all! It will help freshen the air and provide shelter for some of God’s creatures. It can even help prevent some of your downhill or downstream neighbors from being flooded out! All this while adding beauty to your yard and reducing your mowing time! All this could be yours for the low, low price of some rocks, some native plants and a couple of afternoons of sweat equity!
I’m talking about rain gardens and bioswales. Rain gardens and bioswales can be introduced into a landscape to help slow down the flow of water, allowing more of it to soak into the ground. This helps clean the water and alleviates flooding and improves ground water tables. A bioswale is basically a shallow ditch that slopes gradually down from the source of the water, whether that is a parking lot, a roof downspout, a roadway or a driveway. It can be lined with rocks or coarse gravel or eight to twelve inches of leaf compost and sand. It can include some native plants, but not solidly planted. It can be built up slightly on the low end to form a dam to allow two to four inches of water to remain in it and soak into the ground over the course of about two days after a rainstorm. This first level of filtering can remove most of any metals in the water and allows the water that doesn’t run over the low end to continue filtering through the ground.
The next stage of water purification and detention can be accomplished with a rain garden. For many years, building codes and zoning regulations have required detention basins for commercial developments and multiple unit housing developments. These help some, but not nearly as much as they could if they were planted and maintained as rain gardens. The average residential yard could help the water supply by using just 60 to 100 square feet for a rain garden (about the footprint of a mini-van). If commercial, church and development detention basins were to have their sod removed and replaced with a rain garden; it would go a long way to improving suburban and urban water tables and water quality.
A rain garden contains native flowers, bushes and sometimes, trees. 70% of water pollution comes from runoff. 80% of water that falls on a lawn runs off. The idea is to slow down the flow of the water to allow more of it to soak into the ground. Soil and plants filter out toxins to purify the water. Larger plants use more water. Local native plants help purify the air, moderate temperature and provide habitat for birds, butterflies and other creatures.
To build a residential rain garden, first, choose a suitable location. It should be where water flows to naturally, or you can create a bioswale or extend a downspout drainpipe to it. The finished ground level of the rain garden should be eight to twelve inches below surrounding grade level, with gentle slopes into it all around, if possible. It needs to be graded in such a way that the water enters it gently and is evenly dispersed, so it doesn’t erode and the full area is utilized to treat the water. The area needs to be dug down at least a foot deeper than the desired finished grade in order to mix compost into the soil. Then the area is planted with native flowers, bushes and trees. It is important to choose plants which tolerate wet conditions, yet tolerate drought. Local natives work best for this. A few sedges or ornamental grasses may be included in this, but so much that the ground is covered. Remember to choose plants that are appropriate for your sun conditions.
If only local, native plants are used, the rain garden should be very low maintenance. It should not be mowed more than once a year, in the fall.
For photos and more information on rain gardens, visit the following links:
Passive Rainwater Harvesting
Landcare Research (New Zealand), then click on A home raingarden for more detailed instructions and do’s and don’t’s.