Meet your Chicagoland Stormwater Storage Requirements with a rain garden!

Rain Garden Conveyance

ConveyanceIn most cases, your rain garden water source and your rain garden location will not be in the same spot.

Conveyance, the process of moving rain water from your source to your location, can be one of the most challenging parts of installing a rain garden, but it also offers some of the biggest design opportunities.

The addition of rain water can bring movement and life to a usually static garden.

Your conveyance system will usually be dictated by your water source and/or site and will probably consist of one or more of the following three methods:
Grading
Swales
Piping

Grading


Let’s start with the most straight forward method, grading.

Grading is an industry term for contouring the soil surface.

By adding, subtracting, or just moving around the soil, you may be able to create the contours needed to move the water where you want it.

Sometimes just a slight elevation change can make all the difference in getting the water on the right path.

There could be a small hump that keeps water from continuing where it once did, a depression from the house or lawn settling, or a low spot from lawn mower tracks that continues to get worse overtime.

I have found grading to be the most efficient, economical, and low maintenance option of conveyance, but it can not be used is all situations.

Grading can focus surface run-off into one spot, or push along the water for a downspout and sump pump outlet.

In these situations, you will usually want to have at least 3” of drop over 10’ of run to keep the water moving.

A water level or transit can be invaluable in grading work; I will be posting instructions on how to create your own water level for less than $20 on here shortly.

Be sure to lightly compact the soil every 2”-3” as you build up an area.

For maximum efficiency, you can use the soil you remove while shaping your basin to grade the area, but be sure that this soil is relatively dry.

Wet soil does not grade well.

Swale

A swale is basically a ditch, but ditch isn’t a very attractive word, so we say swale.

It is a linear, slightly “U” shaped, Earthen channel used to convey water from one place to another with a constant slope from start to finish.

If you place a swale coming from the house it is especially important to make sure that the swale is constantly pitched away from the house for at least 5’ to 10’ depending on your basement depth, or else the water will sit to close to the house and be picked up by the sump pump drain tile around your house’s foundation.

A swale can be covered with many different materials, but I typically use rocks, turfs, plants, or a combination of these.

Below I will cover the pros and cons of each.

Rocks/Gravel


+ Needed for high velocity sources
+ Adds aesthetic value
+ Require little maintenance
+/- Moderate material costs
High labor to install
May not be desirable aesthetically or economically over long distances


Plants (Bioswale)


+ Good for medium and, if designed correctly, high velocity sources
+ Adds aesthetic value
+ Adds wildlife value
+ Plants add absorption, filtering, of rain water
+/- Moderate to high product cost
+/- Moderate maintenance needed
+/- Moderate to high labor needed to install
May not be desirable aesthetically or economically over long distances


Turf


+ Blends into most landscapes over long distances
+ Good for medium to slow velocity water sources
+ Easy to install
+ Easy to maintain
+ Low cost material
+ Adds valuable play space for smaller lots
+ Economical for long distances
Cannot handle consistent water source (sump pump)
Must be used in a sunny location, with slopes greater than 3” over 10’ preferred to prevent soggy turf conditions


Gravel Grass


+ Blends into most landscapes over long distances.
+ Good for medium and potentially high velocity sources
+ Solid underfoot in shady or low sloped areas
+ Adds valuable play space for smaller lots
+ Easy to maintain
+/- Moderate labor to install
+/- Moderate material costs

Drain tile

If overland conveyance is not an option you can usually use underground piping to get the job done.

This option is usually a little pricier, mostly due to the labor and expertise needed, but small installations are not beyond the beginner’s skill level.

I hope to add some video tutorials on how to properly install drain tile this summer, but for now, I will go over some of the basics of using a drain tile.

You have three parts of a drain tile system
Inlet
Pipe
Outlet

Inlet


Inlet options range from a catch basin to a 90 degree PVC elbow and riser pipe, or, in the case of a perforated pipe, the holes in the pipe itself.

With the exception of the perforated pipe, you want to be sure to maintain an air gap between your water source and your inlet.

This is especially important for a sump pump.

NEVER directly connect your sump pump outlet pipe permanently to ANY outdoor pipe.

In the winter the pipe can clog and freeze shut, forcing the water in the basement to rise up above the sump pump pit and flood the basement.

You will want to keep out as much debris as possible from your inlet with some type of filter, most often used is a slotted grate.

For additional filtration, you can bury the grate a few inches below the grade and then install larger gravel over the top of the grate, using filter fabric around the grate on top of the surrounding soil so that the soil doesn’t flow into the pipe opening which is below the grade; more information to come this summer on filters as well.

Pipe

Below I will briefly cover the two categories of pipe material and then the two categories of pipe styles.

Materials

Polyethylene (PE) -> Flexible, corrugated inside walls, black plastic pipe


+ Relatively inexpensive
+ Handy in steep elevation changes over short distances
+ Typically easier to install
+ Changes directions easily
Weaker than PVC
Flexibility makes it harder to identify poor trench work
Higher likelihood of debris build-up in corrugated ridges of inner walls
Loose connections don’t seal out debris

Polyvinyl chloride (PVC) -> Rigid, smooth inside wall, Green/White/Grey plastic pipe


+ Stronger than PE
+ Rigid pipe shows errors in trench work
+ Smooth inside walls do not hold debris
+ Addition of clean-out allows for snaking, flushing, or other cleaning method
+ Connections are water tight and keep out debris
Need to plan out direction changes with designated angle fittings
Costs about 50% more than PE, but still relatively inexpensive
Transportation can be difficult due to inflexibility of 10′ sections

Styles

Solid – (Both pictures above are solid pipe)
Used to convey water from one location to another.
Can be used in combination with perforated pipe

Perforated


Used to capture water in the soil through openings in the pipe.
PE has slits around the entire circumference of the pipe
PVC has ½” holes drilled out on one half of the pipe
Clean and proper installation largely responsible to the success of either material
Pipe is surrounded by gravel, and either a filter fabric, filter sock, both or none – will discuss this in a future post.

Outlet

That last part of your piping system is your outlet into your rain garden.

A good choice for this task is a pop-up emitter that opens to release water and then closes when the water stops flowing, thus helping to keep debris from getting into the pipe.


Something to be mindful of with the pop-up emitter is that you will want to place the top of the pop-up emitter, the part that the water flows out of and into the garden, above the overflow of your rain garden at least by an inch or so.

This helps to prevent water in the rain garden from freezing over the pipe opening during an overnight freeze after a daytime rain.

You will also want to surround the bottom of the PVC elbow of your pop-up emitter with loose gravel which drains away any water left in the pipe after it is done with moving the rain which prevents freezing water in the pipe.

But if it is possible, I prefer to have the drain tile end laterally and pour the water out directly into the rain garden.

This gives a really great effect and creates movement in the garden while basically eliminating any freezing issues as long as the bottom of the pipe is higher than your overflow by at least an inch or so.

You can see this effect below where I attached an old clay tile onto the end of my PVC piping to give the look of a farmer’s tile surfacing into the garden.



Whether you create an elaborate swale that includes a rock river with plants through out it, or just add a little dirt in the right places to push the water where you want it, the most important thing is that your conveyance system moves the water from your water source to your rain garden.

After you have figured out how you want to accomplish this, you can then move on to how you are going to get some of this water back out of your rain garden with your overflow outlet.

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