Rain Garden Design Series: Part One, Site Selection

Installing a rain garden on your property can be a fun, rewarding experience that will yield benefits for your landscape, community and our watershed! Rain gardens are intended to capture and filter stormwater runoff from impervious surfaces, such as rooftops, roads and parking lots. They are a landscape with a purpose. With good planning, you can have a beautiful addition to your property and help improve and protect our local streams, rivers and lakes.

The wonderful thing about rain gardens is that they can come in all shapes and sizes, and can be as simple or engineered as your property calls for. For the purpose of this series, we will be covering a simple design of a rain garden. This is a three-part series that will cover Site Selection, Design Calculations and Installation. Let’s get started!


Tools/Skills Needed: Percolation Test will require a Post-hole digger, Bucket of Water, Ruler

Costs: $0 if you can borrow the tools needed

Time: 1-2 hours

Level of Difficulty: Easy

 

Understanding Stormwater

It doesn’t take much of a rain event to trigger stormwater runoff. Most of the pollutants we find in the water of our local streams arrive with the first flush of a substantial rain. Few of us realize what an impact a rain garden could make in soaking up (infiltrating) this water.

An average home’s roof is approximately 1,200 square feet. Cover that square footage with one inch of rain water and the roof has quickly generated a volume of 608 gallons of water – or enough water to fill 11 rain barrels! Even a small rain garden can manage a lot of runoff from a disconnected down spout.

Asking yourself some questions before you begin to construct your rain garden will help to avoid unforeseen problems. How does the water flow through your yard? Are there places where the runoff is causing erosion? These are things you will want to consider as you proceed with the design of your rain garden.


Site Selection

It is important to place your rain garden in an area that does NOT hold water. Wet areas of shallow water indicate slow percolation and heavy soils with no infiltration. A rain garden is not a pond or a wetland – it is designed to absorb water, and at the longest, shouldn’t have standing water for more than 24 hours.

Site selection of your rain garden is all about Location, Location, Location! Here are some simple steps to plan the placement of your rain garden.

 

Rain Garden Placement

Rain Gardens are intended to intercept stormwater runoff from an impervious surface, such as the roof shown here

 

Site Selection Guidelines

  • Avoid steep slopes as the steeper the slope, the more digging necessary to make the finished garden level.
  • Be mindful of where the water could possibly overflow in the event of a severe storm.  You don’t want to send water in an unwanted direction such as towards your neighbor!
  • Full or partial sun works best, although rain gardens can also work in shady areas with careful plant selection.
  • Place the garden in an area that will intercept water between a downspout and the storm drain and work with the lay of the land, not against it!
  • Stay at least 10’ from the foundation of your home to avoid water damage.
  • Avoid placement under mature trees as excavation can disturb their precious root systems. (You can plant understory species of trees in the rain garden)

 

Check Your Soils

Conduct a simple soil and percolation test to determine if you will need to amend your soils for better drainage. The ideal rate for rain to soak into the ground is 1-2” per hour. Clay soils do not allow water to soak as quickly as sandy-loam soils, and chances are, if you live here in Northwest Arkansas, you have clay, rocky soils! You can improve your soil’s drainage by amending the soil, which will be covered in Part Two.

Infiltration Picture

Conducting a simple soil and percolation test will help determine if you need soil amendments

 

 

Download this Easy Soil Test

Easy Percolation Test:

  1. Easy Percolation Test Dig a hole about six inches wide and one foot deep.
  2. Fill the hole with water and let it drain completely.
  3. Fill it with water again.
  4. Keep track of how long it takes for the water to drain.

If the water takes more than twenty-four hours to drain, you have poor drainage and will need to amend the soils.

 

Locate Utilities

Most properties have a network of underground utilities such as water, cable, gas, sewer and electric lines underground. To avoid costly mistakes and provide safety for all involved in the installation of your rain garden, you must locate underground utilities.

ARK One CallSafety is important when digging; call Arkansas One Call to Locate Utilities!


Call Arkansas One-Call (1-800-482-8998) or dial 811. They will send a person to locate your utilities and will mark the top of the ground with marking paint or flags. This assessment will be valid for 2 weeks and after that, you will need to relocate to continue the installation. Otherwise, if something were to happen, you would be responsible for repair costs, which can be quite hefty. Don’t risk it, call Arkansas One-Call!

 

Success Starts with Planning!

These first steps will help you to get started with a successful approach to a rain garden installation. Planning is 70% of the process! The Illinois River Watershed Partnership has partnered with organizations and installed over 33 rain gardens in the Northwest Arkansas area! We have learned many lessons, tips and tricks along the way and are happy to assist you with your planning questions and look forward to sharing this experience with you!

 

IRWP Rain Garden Planting

 

Rain Garden Design – Part Two will cover Design Calculations, simple formulas to find out the size of your rain garden, how deep it needs to be and we will discover which plants do well in the rain garden!

 

Related Posts:

Watershed Landscape: Rain Gardens, A Blooming Good Idea!

Watershed Landscape: The Dirt on Soils

Watershed Landscape: Plant This… Not That!