FRENCH DRAIN OR SURFACE DRAIN?
When Determining what type of Drain you need for your Drainage System. In our last blog, we talked about Surface Water and Sub-Surface water and why you need to understand them before designing your Drainage System. If you need to review, click below. If you have a question or comment please leave it at the bottom of the page. I will respond as quickly as I can.
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Before we get into Water Movement, we need to discuss Surface Drains.
Surface Drains come in many shapes and sizes. The two most common are Basin Drains and Channel Drains.
A Basin Drain has a Square Grate and it sits on top of a catch basin. It will have a single pipe connected to it or it will have a drain pipe running into it and a pipe running out of it. We used this picture in a previous blog, but I want to show it to you again.
Surface Drain connected to a Transition Pipe
Below is a Basin before the pipe is connected to both sides. The pipe is cut and connected to one side. Another piece of Drain Pipe is connected to the other side. The Drain pipe does not run straight through the basin. Water must have a way to enter the Drain Pipe. The Surface Drain in the picture is the most common size used in residential applications. The Drain Pipe connecting to it is 4 inch ADS Solid Drain Pipe.
For a Surface Drain to work well it must be placed in a low lying area of standing water. It is not intended to intercept moving water or to drain away Sub-Surface water.
In review, detecting Surface Water is straight forward. You can observe how it flows into the Problem Drainage Area.
Sub-Surface water is not so easy. You can’t see it move into the problem area. So What do you do?
First take a look at your soil. What type of soil do you have?
Soil with a lot of clay will have less Sub-Surface Water, Maybe none at all. If you do have some it will move into the area slowly. If you have sandy soil the underground water will move there in a hurry. Most people will have something in between.
To be sure, a few simple tests can help.
Next check the problem drainage area when there is no water standing in it. Is it soft and mushy when the surrounding area is more firm? This is an indication that Sub-Surface Water is still flowing into the area. Another way to collect information is to dig a small hole about a foot deep in the area. Check it every day for several days. If water is standing in the hole, you have a Sub-Surface Water issue. How fast it flows into the hole is also important.
OK, you have Sub-Surface water along with Surface Water in your problem drainage area. Your Choice for the correct “Intake” for your Drainage System should be a French Drain.
OK, You have no Sub-Surface water. You only have Surface Water flowing into the problem area. You need a French Drain If you are trying to intercept the water as it comes into the area. Many times water will run around the surface drain and still flood the area. Also the Surface Drain is much more easily overwhelmed and water will run past it that way too. Again, this is very important, If you are trying to intercept water before it gets to where its going, don’t use a Surface Drain.
A Surface Drain should be used in a Medium to Low Volume Water situation. The water needs to be stationary or moving very slowly. It should be placed in an area that is the lowest point in the Problem Drainage area. They also work well in smaller confined areas such as pool decks, along sidewalks, or in flower beds.
More than one Surface Drain can be connected to one drain pipe in a “Daisy Chain” of Drains if you have several low spots in a larger area.
In many cases a small french drain can be installed in almost every place that a Surface Drain might be installed. People opt for a Surface Drain over a French Drain because they like the way the Surface Drain looks more than the way the French Drain looks. For some People, Looks are more important than functionality.
Setting the concrete around the channel drain
Channel Drains are set in concrete or dirt but dirt is not always the best idea. Setting a channel drain in dirt should only be done when a shallow surface drain is needed and that is the only option.
Channel drain in concrete
Setting a Surface Drain in Concrete such as a driveway or a Sidewalk is a good application for a Surface Drain. Many times it is better to install a French Drain in your yard over a Surface Drain. What ever makes you happy!
French Drains can be made to look very decorative.
French Drains can be decorated with many types of stone
In conclusions,
French Drains are used for : 1. Higher water volume situations 2. Intercepting moving Surface Water 3. Solving Sub-Surface water problems
Surface Drains are used for: 1. Smaller water volume situations 2. Standing Surface Water that has reached its destination 3. Smaller and more confined areas 4. Set in concrete such as sidewalks or Driveways
