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The Secrets of "Y" Drainage

Benton Landscape Design and Irrigation Company, Inc.

As a Landscape Contractor, John Benton has been involved in drainage installations for twelve years now. His company, Benton Landscape Design and Irrigation Company, Inc., has installed storm drains, french drains, catch basins, dry creek beds, and drainage pits to name a few. When designing a project, they address the storm water run off, the percolation of the soils, the grades, surrounding properties, and the best way to disperse the water.

Some properties present no problems at all, while other properties have serious drainage problems. With the heavy clay soils in this area we have found that amending the soils in beds helps in draining the landscape areas. Installing gutter run off pipes and french drains in areas are often needed in order to solve potential drainage problems.

Benton and his crew review the plans thoroughly to make sure everything is in place. Using laser transits assures the drain lines have the required slope.

With different microclimates Benton often finds a variation of drainage situations on the same property. For proper plant growth it is important to remember that the soil should not only have a good organic content but drain in a timely fashion. The most common causes of plant loss are normally due to either over watering or poor water drainage. This answers the important question, "Why Drainage?"

Site Applications

The project pictured in this article had multiple drainage problems. Of them, this Charlotte, N.C. residence had poor soils that were heavy in clay. Furthermore, the site was full of shaded areas, irrigation problems stemming from over usage of water, and runoff problems from the adjoining residential property. Benton’s crew installed gutter runoff pipes, a dry creek bed, catch basins, and a massive french drainage system in multiple areas. Everything was then tied into a storm-water runoff culvert. With the challenging slopes, heavy shade areas, and summer irrigation needs, Benton installed a "Y" drainage system as shown in the photographs.

Y Drainage

The crew can then place and connect the pipes using either "Y" or "T" connections.

The real secret to drainage is not a question but a solution: Y drainage. That is the design method Benton Landscape Design and Irrigation Company Inc. uses when installing a french drainage system and the main reason it works so well. One long french drain works well as a subsurface drain in a small area, but it is insufficient in large areas. To properly drain large areas of lawn or beds, a more efficient method is to design the french system in a series of Y’s. By doing so, the main drainage line is fed by arms that attach to the main line at a 45-degree angle roughly every 10 to 15 feet. In using the Y method, there are two styles that can be installed.

The first design has arms that insert into the main line from alternate sides and at varying locations. The second design has arms intersecting the main line from only one side of the main line. This design is commonly used on golf course greens, sand traps and tee boxes, so imagine how well it works on a residential or commercial property.

The best and easiest drainage system to install is a corrugated, perforated pipe wrapped in drainage felt. The felt prevents soil particles from entering the pipe and causing blockage problems. There are other products that can be used, such as PVC pipe, Lun-drain, and a reinforced smooth wall corrugated pipe. Benton uses smooth wall corrugated pipe (N-12) by Advance Drainage Systems in heavy traffic areas because it holds up well and is hard to crush.

Drain Installation

Each pipe is wrapped with a drainage felt to prevent particles from entering the drain line. The felt covered pipes are then covered with a layer of 3/4-inch washed stone. Crew members add the washed stone to the entire length of the drain line.

When installing drain lines make sure that the pipe has a minimum of 1 inch per 10 feet of fall. I will have a minimum of 2 inches for 10 feet or better if possible in order to achieve better flow characteristics. To assure that accuracy is achieved, installers are advised to use a transit or contractor level to take elevation readings. By doing so, the contractor can plan the trench depth and the degree of slope for proper flow of the drain lines. Water will not flow up hill, so it is imperative that you maintain a continuous fall in your drain lines.

A "stub up" allows the homeowner or maintenance crew to flush the drain system should it ever become clogged.

When installing fittings and junctions it is important to use drainage tape to secure these fittings. Without the use of drainage tape there is the chance that the fittings will come apart during installation. If Y connections and lateral lines are being used in the design, they should be connected every 10 to 15 feet in order to "wick" out the subsurface water. In heavier clay soil conditions, the lateral lines should be installed at a shorter distance.

To get the best results from the drainpipes, it is suggested that they be placed at least one foot below ground level. Once they have been set at the proper depth and slope, the wrapped pipe should be covered with a washed stone approximately 3/4 of an inch in size. According to Benton, the french drain works best if the top layer (immediately above the washed stone) is covered with a decorative stone, mulch or pine needles. If the drain is installed under a lawn, the stone should be covered with 2 to 4 inches of soil to allow for root growth of the grass.

It is wise to place a "T" or "Y" in the drain line and bring an opening to the surface in one or more places. Doing so provides access to the drain line should it be necessary to flush out any blockages in the drain. Where the pipes meet the ground level is a good place to install a catch basin. However, if a catch basin will not work, the pipe stub can be simply covered up with a cap. Benton will place small catch basins at the openings in lawn areas to catch surface run off where possible.

Many sites require the trenches to be hand dug due to wet conditions. When equipment can be used, the trench should still be cared for by hand to produce the desired slope needed to create proper drainage.

Designing and installing a french drainage system with the correct design, pipe sizes and slope will not only prevent plant loss but will encourage proper plant growth. According to Benton, bed preparation and proper drainage is more important than the size of the plant installed. In the long run the homeowner benefits from an educated contractor who knows these principles.

The national CLT (Certified Landscape Technician) exam is an excellent way to learn this. Most states offer a Certified Landscape Contractor exam and it is another great tool for learning correct drainage installation techniques. A good education on drainage is just as important as an education in landscaping and irrigation.

John Benton and his staff of 35 employees have been installing commercial and residential landscape projects for 13 years. He is a Certified Landscape Contractor in North Carolina, ALCA Certified Landscape Technician, Certified Toro Irrigation Contractor, Certified Nightscaping Contractor, and became a South Carolina Master Gardener for the fun of it. hello


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October 20, 2019, 6:08 pm PDT

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