Wednesday, May 11, 2011

So what is a Rain Garden anyway? Post 11.1

Welcome to the Perkiomen Watershed Conservancy’s Rain Garden blog. In our first article, we discussed why it is so important for all of us to be mindful of our stormwater management methods and for each of us to find ways to slow the flow of stormwater so more of it can soak into the ground and recharge local water supplies. We are losing a valuable resource when we flush our stormwater quickly into local streams and damaging critical aquatic resources in the process.

So how do we slow the release of stormwater without having our properties become a quagmire of soggy soils? Since the title of our blog is Rain Gardens, why don’t we start there!

The term “rain garden” can be slightly misleading, conjuring up images of watery gardens or soggy wetlands but really the term relates to the rain or stormwater that the garden is designed to absorb. A more accurate name for this garden might be a stormwater garden, but that sure doesn't roll off the tongue so easily.

Rain gardens have a very specific function and need to be constructed with this function in mind. The well-designed rain garden will collect, store and drain stormwater runoff, allowing the water to slowly infiltrate into the ground where it will be cleaned by the soil and help recharge local groundwater supplies. (Just a note – the natural ability of soils to mechanically, biologically and chemically clean water is well known. However, it is the slow movement of the water through this amazing natural system that allows the cleaning actions to occur. So slowing down the flow of stormwater is critical to reducing stormwater damage as well as recharging our local water supplies.)

Rain gardens mimic the natural functions of upland forests and meadows. The vegetation and shape of the garden help slow the flow of stormwater. The bowl-shaped depression of the rain garden is similar to the many small depressions and undulations of the natural landscape that allow rain water to stand long enough to slowly soak into the ground. And the specific soil mixtures of a rain garden help rainwater infiltrate through the soils to be filtered and cleaned. 

Once completed though, you may not notice much difference between a rain garden and other gardens except than one is a recessed, shallow bowl while a regular garden is often a molded, raised bed. But there are three unique components of rain gardens that must be considered during the initial construction.

1.      Each rain garden must have a defined entrance area where the water drains into the garden. This can be a pipe or downspout or a shallow swale that leads to the main part of the garden.
2.      The main feature of the garden is the recessed planting bed, which should be flat and level throughout.
3. A mounded berm around the three downhill sides the garden with level edges and even height allows the water to be retained in the garden area until it is absorbed.  The berm will be highest on the downhill side tapering off as it meets with the uphill side of the garden. Depending on the slope of the area the berm may be small or large.

Planning is imperative in order to create a properly functioning rain garden. Soil conditions, the amount of sunlight and the size of the drainage area will guide your garden planning. These issues will be addressed in the next Perkiomen Rain Garden Blog. To get a head start, make some notes about how much sun or shade your potential rain garden will receive. If you are feeling energetic, you can do a percolation test, or perc test, to see how fast your soils drain. Start by digging a small hole about 3 foot deep. Fill the hole with water and let the hose run for a few minutes after the hole is full. Then see how long it takes for the water to drain away. The faster the water drains, the better the test results.

The Conservancy is a private non-profit organization established to conserve and protect the land & water resources of the Perkiomen Creek watershed. We are located in Schwenksville, PA but work throughout the Perkiomen Creek's 362 square mile watershed. We are committed to excellent environmental education and practical, effective, hands-on conservation and stewardship efforts aimed at improving water quality and aquatic habitats.

The Conservancy is also a founding member of the Perkiomen MS4 Partnership whose goal is to help member municipalities address the public awareness and participation requirements of the PaDEP and US EPA's Municipal Separate Storm Sewer System (MS4) programs. The overall goal of this blog will be to provide general information about stormwater issues and specific information about rain gardens. We hope you will follow us as we explore these interesting and important topics with our communities.