French drains are often
required to remove excess water from low spots or excessively wet
areas of the lawn.
type of area is often located behind a house, at the base of a
slope, where excess run-off is directed to a lawn area that's nearly
level. Other times, the wet area might be along property lines where
two adjoining lots were graded separately. Whatever the case may be,
the goal is always the same: move water away from the soggy area.
Once the decision is made to install a french drain, the next step
is determining where to end the french drain, and where to send the water. In
most situations, the best place to channel the water is toward the
front street curb, if you're on the high side of the street, but this presents
other potential problems.
WHERE TO THE CHANNEL WATER
>> TO THE CURB: Piping
storm water to the curb, and dumping it into the street, is often
done with downspout connections in new building plans, especially when they can't be
tied-in to existing storm sewers. Most storm sewer systems have been
engineered for set flow rates, and it's usually difficult to get
permission to tie-in to an existing storm sewer, even though this is
the ideal solution.
The biggest problem with water dumped over the
curb, is it ices-up in northern areas with a winter
season. In freezing weather, the steady flow of underground water can create large
"ice flows" along the curb, that create a sliding hazard to pedestrians and
vehicles. In summer, water flow along a curb can create algae, as
well as a favorable environment for mosquitoes.
connecting to a storm sewer requires advance permission from your
local municipality. Therefore, if you must send water to the
curb area, check applicable local laws and ordinances first.
French drain we saw in our travels...
It was installed at the top of a slope
to intercept water runoff from above.
Water flow was piped to the curb.
>> INTO A DOWNSPOUT: Tying
your french drain into an existing downspout is another solution.
This is often done when no other solution exists. The biggest
downside to this type of arrangement is that you are sending water
back toward the foundation area of the house. It's not uncommon for
these downspout and foundation areas to already have drainage
problems that cause wet basements. Adding to that foundation water flow can
aggravate many existing problems. Often times, downspout pipes and french drain pipes around the foundation of a house become
disconnected as soil settles over the years. Therefore,
before electing to use this solution for your french drain, make
sure everything is connected properly underground so that you won't
be adding to any existing problem with wet basement walls.
>> OVER THE HILL: With a large enough building lot, it's often possible to direct french drain
water onto the surface of the lawn. In effect, this only moves the
wet area to a different part of your property, but in the right
situations, this solution works well. Remember never to direct water
onto a neighbor's property.
>> INTO A DRY WELL:
Old-timers often used a drainage solution known as a dry well. A dry
well is nothing more than a large hole in the ground, backfilled
with rocks or large gravel. Water is piped into the dry well with
the intent of it percolating out of the dry well into the
surrounding soil. In ideal situations, with soil that drains rapidly,
this solution works well. However, if the surrounding soil is heavy
clay, the dry well may only act as a bath tub, filling with water,
which then flows backwards up the french drain pipe, re-flooding the
area you are attempting to drain.
FRENCH DRAIN CONSTRUCTION
>>LOCATION: French drains should
run along the center
of the low area(s) needing drained, and end at the desired drainage
point. There should be adequate "fall" in the french drain
construction, for water to naturally run downhill, toward the drainage end.
>>BEFORE DIGGING: Before doing any digging, contact your
local utilities to have them mark buried utility lines. This can
usually be accomplished with one phone call to your state's ONE CALL
system. It usually takes 3 to 5 weekdays for all the utility lines
to be marked, so plan ahead.
>>TRENCHING: The next step is digging a narrow trench
to accommodate the perforated pipe and gravel. It's best to do your
digging during a dry spell, when soil is much easier to work. Depth of the trench
is usually 18 to 24 inches deep, depending on the application, with
the width of the trench around 12 inches or more. The "floor" of the trench
should run downhill toward the drainage end of the pipe, to encourage the natural
flow of water.
Note: You may want to first cut and remove lawn sod from the
excavation area for later replanting, after the french drain is
installed. Otherwise, you will have to reseed the disturbed lawn area.
>>INSTALLATION: First, the ditch should be lined with
landscape fabric, making a "U" shape with the fabric
laying in the trench.
Next, lay the perforated pipe in the trench. Several types of
perforated pipe are available. The flexible black pipe that comes in
100 foot rolls is easier to work with than rigid sections of
perforated pipe, but it isn't as strong. You may need to buy various
pipe couplers to fit the pipe together.
>>GRAVEL: Place 2b limestone (or equivalent) gravel
around the the sides of the pipe and cover the top of the pipe with
gravel, leaving enough room to finish off the top of the trench with
at least 6
inches of topsoil (some installers like to run gravel all the way to
the surface). Once the gravel is in place close the fabric over
top of the gravel to prevent dirt from sifting down into the
gravel and clogging it. If there isn't enough fabric to cover the
top of the gravel, cut a new length of fabric for that purpose.
>>SOIL BACKFILL: Once the fabric is in place, finish
filling the trench with topsoil. If you are seeding the area, bring
the grade even with the existing lawn. If you are using sod, leave
enough room for the thickness of the sod to bring the grade even
with the existing lawn.
>>WATERING: Be sure to water the sod or seed as you
would any newly planted lawn area, to ensure proper establishment.
>>NOTE: For best all around results, the finished
(surface) grade of the lawn should have a natural slope, to encourage
surface water to runoff when the soil and french drain are frozen.
Stone & Gravel