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If you've ever
read about Paris in the 1930s, you will have an
understanding of the French drain葉he sewers of
Paris were known worldwide for being nothing more
than open trenches filled with human waste. Not
too classy for the most elegant city on earth!
But these days even Paris has succumbed to the lure of
inastalling pipes and wastewater management, and the open sewer is
just a rank memory in all but the worst of slums. Building a french
drain remain widely useful, although not for
sewage葉hey are perfect for diverting rainwater from
foundations, basements, driveways and other places you
would rather keep dry. French drains can in some cases
be installed without pipes, by laying beds of gravel down in
trenches under the topsoil, but for most building codes
and to keep the water moving right where you want it,
laying in a series of pipes makes the most sense.
Flooding occurs when the topsoil, which contains a lot
of air, becomes saturated with water. If the area isn't
level, the water will flow downhill; if there's no
slope, it will stand where it is, taking a long time to
work its way into the more compacted and often clayey
soils beneath. Water that would normally flow downhill
in a sheet of liquid topsoil finds it much easier to
move through gravel and pipe, so it will naturally find
its way into your trench.
If the slope in your yard isn't perfectly obvious,
rent a builder's level to help you find the high and low
points in the area you want to design a drain. Your yard may look
fairly flat, but sometimes, although the slope isn't
apparent to the naked eye, it's sufficient to send water
on its way downhill. A level will help you find the
lowest part of your property, which is where you'll want
your pipe to exit the ground.
You can control flooding around your house by digging
a narrow trench about 6 inches wide and about 2 feet
deep that wraps around three sides of your house and
heads downhill. Dig the trenches in a U shape around
your house, keeping the ditch between four and six feet
from the foundation of your house. Once you have your
trench dug, compact the earth in the bottom of it, and
place your drainage pipe into the trench. Make sure the
holes in the drain pipe are pointing down into the soil,
or your trench won't work because the holes will be
immediately clogged with dirt. This is really
important様ots of people doe everything right but then
screw up the pipe by putting it in upside down, so their
trenches never work. Point the holes down!
Once you have the pipe installed, cover it with 1
inch (or greater) washed, rounded gravel, filling the
trench until it's one inch from the surface of the
ground. You can then place a strip of sod or soil
planted with grass seed over the trench to make it look
nice and help keep the gravel in place. If you have
problems not just with sub-surface water but with water
standing on top of the ground as well, you can just fill
the trench all the way to the top with gravel: this will
increase your drainage. If the sight of the trench will
bother you, you can make it wider at the top and put
some curves into it when you're planning its course, so
that the gravel becomes a winding path.
You don't need tons of expensive equipment to install
a French drain system. Any time you're planning to dig
into the ground, you should start by making sure there
are no underground utility lines in the area you're
planning to trench. Buried electric cables, sewer or gas
lines can kill you if you dig into them. At the very
least, you may cut into a sewer line and make a big,
expensive mess. So, make sure you know there's nothing
else buried before you start to dig!
You can rent a ditch digger or trencher (also called
the Ditch Witch) from a place that rents building
supplies, and you can buy the perforated drainage pipe
from most hardware or home supply stores. The builder's
level is also something you can rent, and you can either
pay to have the gravel delivered, or if you have access
to a good sized truck, you can buy it much, much cheaper
if you pick it up yourself. If you're not confident in
your ability to calculate the amount of gravel you'll
need, take the measurements of your trench (6 inches
wide, 24 inches deep, 200 feet long, for example) to the
place where you buy gravel and ask someone who works
there to help you calculate the amount of gravel you
need to buy. (This is good advice if you're near a
building supply store that's not one of the huge chains:
too many of the giant home stores employ teenagers who
don't have a clue about how to help you.)
What's a Trench Drain?
You may hear the words "trench drain" and "French
drain" used interchangeably, which can be confusing when
you're contemplating at home drain repairs. "Trench
drain" means different things to different people, for
the lay person, it's a drain that's constructed by
digging a ditch or trench and either laying gravel,
pipes or both into the drain. Trenches are used in
creating French drains, which are ideal for draining
water away from houses or from land into storm sewers,
catchments or other areas where the water won't pose as
much of a problem. But to experts, trench drains may
mean large, industrial drain systems that are built with
trenches miles long and a hundred or more feet deep.
Used in road building, city sewer systems and municipal
drainage, trench drains are often the foundations on
which entire cities rest.
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