Granite Rip Rap Drainage Swale

Key Requirements:

Several constraints had to be satisfied in the construction of the swale:

1. The Home Owner’s Association (HOA) Covenants mandate the “flow of water on the property cannot be changed“. i.e. No building of walls or berms that might flood your neighbor.
2. Due to the steep grade, the swale needed to lined with rubber sheeting and armored with rock to prevent undercutting and to slow down the water.
3. The swale had to look “nice”.

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.

Materials:

The materials used in the is project are:

• 19 tons of granite rip-rap hauled in by dump truck from a local quarry, ~$400 for materials and hauling fee.
• ~120 feet of Firestone EPDM PondGard rubber geomembrane liner, ~$450.
• 6 inch sod staples
• Labor cost @ $1300

Construction:

After consulting with a local landscaping company, a rubber-lined channel with granite rip-rap rocks was decided upon. The width of the swale was determined by the landscape company from past experience. Due to the amount of material and the ~120 feet length, this was no job for the do-it-yerselfer. A team of 8 men worked two days to dig the trench, place the rubber liner and set each stone by hand.

First, the trench was dug by hand with picks and shovels.

Second, the bottom of the trench was lined with Firestone EPDM PondGard .45 mils rubber membrane. PondGard is a very tough and durable material that’s used for building ponds and widely available at landscape supply stores. For this project, a wider roll was cut to width. The liner is overlapped higher-over-lower at the joint midway down the hill, like a roof shingle.

Firestone EPDM PondGard Rubber Liner

The rubber liner is held in place by 6 inch sod staples, also available at any landscape supply store.

6 inch Sod Staples

Here’s a closeup of the .45 mil PondGard rubber liner exposed by moving a few rocks.

PondGard Rubber Liner

Next, the granite rip-rap was carted by wheelbarrow from the front driveway and place by hand in the swale. Sheets of plywood were laid on the driveway it wouldn’t be scarred when the dump truck dumped the load of rock. Kudos to the landscape crew as they worked with great care to place each stone just right and avoid any damage to the PondGard liner.

Finally, the roof gutter downspout drain lines were buried and routed into the swale. This greatly helped to keep excess moisture away from the house foundation and basement and further reduced any potential for cutting gullies in backyard.

Remember the Homeowner’s Association rule the “flow of water on the property cannot be changed“? Well, the neighbor’s gutter drain pipe was “conveniently” routed to edge of their property line where it promptly emptied into my backyard. I simply tied their drain pipe into the swale solving that problem, too.

The results have been great! Worth every penny.

Rock Swale

As an extra touch, ferns were planted along side of the swale to soften the view.

Bob Jackson

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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

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

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

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

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

Hope this helps,

Bob Jackson

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