Building a Grassy Drainage Swale

Landscaping

Grassy Drainage Swale

Grassy Drainage Swale

A grassy drainage swale can solve standing water problems. The advantages of a grassy swale are:

  • Nice appearance
  • Inexpensive to install
  • Easy maintenance
  • Can run the lawn mower across a gentle slope
  • Effectively drains the water

Things to Consider:

Before installing a drainage swale, consider the following factors:

  1. Where is the water coming from? Standing rain water? Or is the water flowing onto the property from elsewhere?
  2. Where should the water go? Water always flows downhill. Is something preventing the water from draining away? Is a storm drain clogged with debris? Is a drainage ditch overgrown with weeds or full of mud? Is some man-made barrier blocking the waters natural path?
  3. How much water to be handled? Is a wide drainage channel needed or will a shallow channel suffice?
  4. How steep is the slope? A gentle slope will have a slow current, while a steep slope will need breaks to slow the water and prevent erosion.

The yard at this house in the photo below is very flat and suffered from flooding during heavy rains.

Flooded Yard

Flooded Yard

Why the Yard was Flooding:

The flooding and standing water problem was caused by an overgrown and mudded-in drainage ditch that couldn’t handle the rainwater runoff. The drainage ditch is hidden behind the wood fence along the back of the property line in the above photo. Annual maintenance of the ditch had been neglected for so long tall trees and weeds now grew thick.

Fixing the Floording Problem:

The flooding problem was solved by:

  1. Contacting the County Stormwater Management Dept. (this function may be within the County Dept. of Transportation in your area) to clear and dredge the drainage ditch. The Stormwater Dept. promptly performed the clean-up and repair work because the drainage ditch is connected to another ditch by a county maintained road just upstream. I said to the County representative “You’re putting the water into the ditch, it’s your responsibility to make sure it handled properly.”
  2. Building a grassy swale and burying a 6″ PVC drain pipe that emptied into the canal.

The results were very satisfactory.

How to Do It:

  1. The County Stormwater Dept. cleared the overgrowth and dredged the drainage canal as shown in the photo below. The county used a 40-ton trackhoe to cut down the trees and weeds. A Gradall excavator dredged out the mud and contoured the sides of the ditch. The rotted wood fence (see above photo) was removed and replaced with a post and wire farm fence as seen here on the left.
    Cleared and Dredged Drainage Canal

    Cleared and Dredged Drainage Canal

  2. Next, a tractor service was hired for $600 to dig two swales roughly 200 feet in length on the left and right sides of the property line. The main trench was made by a single-furrow v-blade plow. The depth of the swale began at ground level and increased to about 1 foot at the far end. The sides of the swale were then graded and smoothed using a flat scraper blade tractor attachment.The slope of the swale is very gentle and no lining material for the bottom was necessary, other than grass seed / grass to hold the soil in place.

    Digging the Swale

    Digging the Swale

  3. A 6-inch PVC drain pipe was buried on a 1/2 bubble slope (set using a carpenter’s level) that emptied into the drainage ditch. The mouth of the drain pipe was cemented to prevent erosion.

    Buried PVC Drain Pipe

    Buried PVC Drain Pipe

The Swale At Work:

The swale worked great during a heavy rain and thunderstorms. Notice the swale full of water from left-to-right in the photo below. The water would pond temporarily only during the heaviest downpours and the yard is high and dry soon after the rain had stopped.

Swale at Work in Heavy Rain

Swale at Work in Heavy Rain

Hope this helps,

Bob Jackson

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2 Responses to “Building a Grassy Drainage Swale”

  1. NORMAN CAMPBELL Says:
    May 29th, 2009 at 12:03 am

    PLEASE ADVISE ME WHAT TYPE OF LAWNMOWER OR MOWING EQUIPMENT THAT YOU WOULD RECOMMEND THAT I USE TO MOW MY SWALES. BEAR IN MIND THAT THEY ARE TYPICALLY WET ESPECIALLY AFTER A SHOWER OF RAIN. ASIDE FROM A WEEDEATER WHAT MOWER OR EQUIPMENT WOULD MAKE THE JOB LESS LABOR INTENSIVE AND EFFECTIVE?
    tHANKS FOR YOUR REPLY TO MY EMAIL ADDRESS.

  2. Bob Jackson Says:
    May 29th, 2009 at 6:55 am

    Use the lawnmower you already have, that’s the idea behind a shallow grassy swale. If the swale is too wet or has water in it, such as Florida’s summer season, use the weedeater to cut the grass to just above the water level.

    A good swale should drain completely within a few hours to a day after the rain stops. You might want to check the slope for proper runoff.

    Take Care,
    Bob


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