Rain gardens are a simple and effective way to decrease or in some cases eliminate the harm done by runoff caused by rain coming off the roof of a building or by poor drainage situations. A suitable area in your yard is located and is dug and shaped to capture the waters coming out of gutter drains or water rushing off driveways, patios or roads. The garden is planted. This garden then will release the water by letting it infiltrate back into the ground, thus eliminating runoff and the harm caused by runoff. Plant material installed into the garden, hence the name rain garden, aids in the removal of pollutants and helps keep pore space in the soil open with healthy root growth. Not only do rain gardens benefit greatly with storm water management, but they are also a beautiful, colorful garden that attracts and benefits wildlife. Water in this rain garden is not intended to remain. It should seep into the soil. The purpose of the garden is to allow water to infiltrate – not pond! Mosquitos will not have enough time to grow in these situations because a mosquito requires 10 to 14 days from egg to adult.
Typically in a storm, surface runoff gathers strength and speed as it flows downhill. It picks up many kinds of pollutants, causes erosion and if left unchecked, ends up flowing directly into our streams, lakes and rivers. By installing a rain garden on your property you will be doing your part to eliminate these problems.
The size of the garden is dependent upon the volume of water to be captured, the soil conditions present on the site and the slope of the land. Infiltration is mostly affected by the type of soil. Typically a well drained soil has sandy or boney conditions and will allow for faster infiltration. The reverse is true for more clay like, finer soils, which decrease the rate of infiltration and call for a wider garden area. In some situations amending the soils to aid in better drainage is necessary. As the water percolates into the soil it is being cleansed of pollutants during it’s journey through the soil layers. Soil is an amazing purifier, just think of the science behind the typical household septic leaching fields. Rain gardens also aid in the recharging of clean ground water.
Another great thing about designing a rain garden is versatility. They can be any shape and can be combined with other storm water management techniques to improve function, such as rain barrels, planted swales, weep walls and planted steep slopes. In tighter areas you can install a two tiered rain garden. Larger rain gardens can even accommodate shrubs and trees. In one instance we designed a rain garden for adjoining neighbors which also acted as a privacy hedge.
Weather patterns have become much more intense with storm activity and rain falls increasing. When designing a rain garden it is important to allow for overflow. The high level overflow can be the height of the berm or can be a designated and designed area at the highest point of the basin to allow excess water to escape. Typically the excess water is allowed to flow into an existing drain or allowed to flow towards other gardens or other storm water management areas already in place. However much water your rain garden can accommodate and allow to percolate into the ground is that much more clean water for everyone. Even if some water does overflow, your rain garden is an important check point to slow the velocity and aid in capturing pollutants.
The native plant material installed in a rain garden is an integral part of the function. The roots of the plants help maintain pore space in the soils. The plants take up some of the water during growth and also bind certain contaminants. The plant material chosen for a rain garden depends upon the soil drainage factors or how long it will be inundated with water. We approach the rain garden like many other gardens in how we install the plant material. It is important to have a layer of decent growing medium in the rain garden. After installing the plants we also add a layer of shredded bark mulch that aids in plant growth, keeps the weeds in check and in time, will create an area of microbiological activity that will break down pollutants into inert ingredients.
By creating a rain garden you will lessen or even eliminate the harmful effects of runoff. You will allow for a positive way for water infiltration, help with reduction of pollutants in ground water and our rivers and lakes and add color to the landscape while providing habitat for wildlife.
For more information visit www.sustainability.uconn.edu