Main Menu


How to Build a Grassy Drainage Swale

Yard Drainage Swale

Yard Drainage Swale

A grassy drainage swale can solve standing water and yard drainage 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

Drainage Swale Construction Planning

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 Caused by Poor Drainage

Flooded Yard Caused by Poor Drainage

Why the Yard Flooded

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 that it was choked with trees, weeds and mud.

Fixing the Flooding Problem

The flooded yard 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.

Grassy Drainage Swale

Grassy Drainage Swale

How to Build a Grassy Drainage Swale

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 the first photo above) was removed and replaced with a post and wire farm fence set well back from the ditch to provide access for the county’s heavy equipment to maintain the ditch.

Cleared and Dredged Drainage Canal

Cleared and Dredged Drainage Canal

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 and grass to hold the soil in place.

Making a Yard Drainage Swale

Making a Yard Drainage Swale

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.

Yard Drainage Swale - PVC Drain Pipe

Yard Drainage Swale – PVC Drain Pipe

Grassy Drainage Swale in Heavy Rain

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.

Grassy Drainage Swale in Heavy Rain

Grassy Drainage Swale in Heavy Rain

Hope this helps,

Bob Jackson

Copyright © 2014 HandymanHowTo.com   Reproduction strictly prohibited.

RedditEmailShare

,

4 Responses to How to Build a Grassy Drainage Swale

  1. NORMAN CAMPBELL May 29, 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 May 29, 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

  3. guest June 28, 2011 at 12:41 pm #

    Can you get the same results with a 4″ sock pipe? My neighbor has filled in the drainage swale in his yard and replaced it with a sock pipe system. He wants us to do the same. I’m not sure. The swale is ~6ft wide and about 2 feet deep when it fills up. I don’t see how that little pipe can diplace all that water.

    • Bob Jackson June 28, 2011 at 9:05 pm #

      A 4″ corrugated slotted pipe with a polyester sock (sock pipe) is suitable for low volume drainage when covered with gravel and maybe soil for a grassy surface finish. The purpose of the sock is to keep out dirt and rock so the pipe doesn’t clog.

      The sock pipe can be used in two ways:
      1) Pipe the water into the mouth (high end) of the sock pipe so the water can soak into the soil over the length of the pipe. The pipe in this application has no surface outlet, similar to a septic tank drainage field. This requires an elevated drain field so the water will flow into the surrounding area.
      2) Lay the pipe in a ditch, cover with gravel (and optionally soil) to take in the water along the length of the pipe to the open discharge end located at a more distant lower elevation.

      The problem with a 4″ diameter sock pipe is the area of the pipe is only 0.09 square feet versus 12 square feet for a rectangular (6 ft wide x 2 ft deep) ditch. Let’s assume the ditch is roughly V shaped instead of a rectangle, then the V ditch has maybe 6 square feet of cross sectional drainage area. The open ditch with 6 square feet of cross sectional area has about 66 times greater drainage capacity (=6 sq ft divided by 0.09 sq ft) compared to the 4″ diameter sock pipe. In other words, you’d need at least 66 of the 4″ inch sock pipes stacked together to equal the drainage capacity of the open ditch. In reality you’d need more than 66 sock pipes due to friction losses of the many pipes.

      I buried a 6″ PVC pipe at the end of the swale to empty into the large ditch at the back yard because a 6″ pipe was the largest size sold at Home Depot. I would’ve bought a 10″ PVC pipe if they sold it.

      The 6″ PVC outlet pipe emptied my swale in an hour or so after a heavy rainfall. Overall it did great job of preventing the ponding problem and water would continue to drain in smaller amounts after a day or two of wet weather.

      Remember that I started from a flat yard with no swale and was guessing at how big a drain pipe would be needed to handle the water. If the 6″ outlet pipe didn’t work, then I would have replaced it with a larger pipe. It’s obvious your swale that fills with 2 feet of water can’t be replaced with a 4″ pipe that’s at least 66 times too small.

Leave a Reply