French Drain, Do It Yourself, DIY, French Drain Information, Necessary Details, Drainage Trench —

Posted: February 20, 2020 in DIY Drain Installation, DIY French Drain, Drain Installation, Drain Repair, french drain
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French Drains and all types of Drainage Systems involves digging Drainage Trenches and Installing Drain Pipes.  One issue that must be addressed is Slope or Fall” of the of the Drain Pipe in the Drainage Trench.   The Drain Pipe must run downhill to the exit point to move the water away from the problem area.

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drain trench

Drainage Trench Running Downhill


Gutter to French Drain

Connecting Gutter to French Drain

In many cases slope is easy to determine if the distance from the drain to the exit is obliviously down hill.   The trouble is installing a French Drain or a Drainage System where the drain pipe is not always on a pronounced slope.  A slight slope can be hard to see. If the ground looks level then the water won’t flow very quickly, If at all.  If the entrance drain is slightly higher than the exit, say only a few inches, then the water will flow across level ground to the exit point.  Problem is, the water will move very slowly as long as water is still coming into the French Drain.  It pushes the water in front of it out of the exit very slowly.  Movement will stop when water stops coming into the Drain.  It will stay in the pipe and just sit there till the next time it rains.

If you are Installing a Drainage System across level ground, it will never drain very well.

If you are not sure if a Drainage System is possible because there might not be enough Slope,  there is a simple test you can run.  This test takes a good bit of digging.

Start digging the trench where the drain pipe will run.   Lets say for example that its about 60 feet.  Start digging where the drain will be.  Typically a 4 inch drain pipe will need to be installed in a trench 8 to 16 inches deep, depending on your needs.  Dig about 10 feet from where the drain will be toward the exit point.  Once you have dug a trench at least 8 inches deep, and about 10 feet long toward the exit,  Take a hose and place it in the trench where the drain will be installed. There should not be pipe in the trench at this time, just the empty trench.

Turn on the hose so a small amount of water is coming out.  The water will start to flow down the trench from where the drain will be, toward the exit.  Again there is no drain pipe in the trench.

trench water test

Water test for a Drain Pipe

Watch the water as it flows down the Drainage Trench.   In some areas it will flow quickly which is good.  Look for areas where water flows more slowly and begins to pool.  Once this occurs, turn off the hose and get your shovel.  With water still in the trench, dig downhill from the pooling spot.  Remove the dirt that is slowing the waters flow toward the exit.  Repeat this process until you have reached the exit point of the Drainage System.

This may seem like a lot of unnecessary work.  Believe me it is worth it.  Once the water flows at a fairly steady rate all the way to the exit, you have ” Set the Flow of the Drain.”

This process is called “Setting The flow.”

There are benefits to taking this process seriously.

First it will tell you if the flow is even possible for the Drainage System that you want to install.  If you can’t get the water to flow to the Exit Point Cover up your Drainage Trench and Consider Other Options because this particular Drainage Design will not work.  If you can redesign your system by moving your drain pipe or your exit point, then do so.  A Sump Pump may be your only option if moving the drain pipe or the exit does not improve things.   Sump Pumps will be covered in a future blog.

Second, If you were successful in setting the flow, then you will roughly know how fast the water will flow in your Drainage System.  It will give you a “Worse Case Scenario” for your Drain’s Performance.

Water will always flow better and faster and more efficiently in a Drain Pipe, than in a trench.

If the water is flowing pretty good in the Drainage Trench without a Drain Pipe in it yet, then it will flow even better once the Drain Pipe is installed.

This process is much better than blindly digging a drainage trench and installing a Drainage System.  It will keep you from installing something that doesn’t work!

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