Rain Gardens
By Joe Monte
Water usually gets second billing behind oil when the topic turns to resource conservation. This is odd considering humans don’t need to maintain their current appetite for oil in order to survive. Unfortunately, humans are almost as efficient at depleting aquifers as they are at depleting oil deposits. This alarming feat has galvanized many people to adopt new practices that conserve fresh water. One method gaining popularity is to install a rain garden. These are garden features that are designed to hold water during a storm event and release it slowly into the ground.
Until recently, conventional drainage systems were designed to transport large volumes of storm water as quickly as possible to streams. This practice overtaxed city drainage systems and has not been popular with stream dwellers (ask a salmon). The new approach aims to recharge aquifers by mimicking natural systems. While natural systems are complex and diverse, they can be scaled to any size, and maintenance is optional. After the initial excavation and planting, the garden will ‘operate’ itself. Rain gardens are located in low lying spots where water can collect. If you don’t have a natural depression, the excavated soil can be used to create different grades. Rain gardens should be sized properly so they can handle the amount of water directed to them. The water should percolate within one day. Plants that can tolerate wet feet as well as dry summer spells should be the first choice for the zone.
Depending on the size and slope of the rain garden, there is a great opportunity for a variety of plants. In the lowest area, plants with a substantial root system are better suited to handle an influx of water. Streamside plants, like a bush dogwood, would be a great anchor for any design. At the upper area, more drought tolerant ground covers make sense. When making your selections, keep in mind plants that attract birds, butterflies, lizards, or frogs.
Lawn areas are too compacted to hold and absorb as much water as rain gardens but the two do work well in tandem. Replacing a section of lawn with a rain garden is a great idea. Lawns can filter out sediment, the number one polluter of storm water. As you drive through the construction zone on Highway 12, you’ll see black cloth under all the storm drains. Cloth works, but doesn’t look very ‘green’. Go for the English garden look, but use plants more suitable to our climate.
Man-made rain gardens are usually constructed in the built environment. This setting presents design challenges and opportunities. With any new construction, rain gardens can be one component of a drainage system or greywater catchment system. Strategic placement of rain gardens can reduce infrastructure, flooding damage, etc. by collecting water from nearby impervious surfaces. Even on small residential sites, they can be part of a larger system. Rain barrels can collect and hold roof runoff until the ground is less saturated. Then, water can be directed to the rain garden. Unlike most green retrofits, installing a rain garden doesn’t involve dumping the old product; there should be no waste. They also reverse the depletion of natural resources, which results in incalculable future benefits.
If you are worried about water quality from street or roof runoff, consider compost and manure. Organic material accommodates microbes that trap and convert metals, hydrocarbons (oils), and other toxins to more benign substances. Use a thin layer of compost on lawn, not fertilizer which can lead to drastic nutrient imbalances in water. Look at the ‘dead zone’ in the Gulf of Mexico created by habitual fertilizing in the Mississippi watershed.
Several years ago, people in Seattle were skeptical of rain gardens when they were first proposed alongside curbless streets. Now neighborhoods are clamoring to have their streets redesigned. Rain gardens not only work, but they can also be aesthetically pleasing. It goes to show you can’t always go with the flow, sometimes you have to slow it down.
