The problem with doing a "Goggle" search is the fact that you
will get thousands of hits ranging from absolutely uneducated
to somewhat good. Advice from "experts" is also variable and
sometimes unreliable. I've done a fair amount of research on the
subject and consider the following book to be one of the best:
Practical Drainage for Golf, Sportsturf and Horticulture
This is a $50 book, but it is available from any reasonable-sized
library system. The authors discusses many of the misconceptions
of drainage systems, such as the historical advice that course gravel
(or any gravel) is the optimal fill material. The authors are British and
have analyzed the failures of many extremely expense professional
drainage systems which were installed using conventional wisdom.
Many school fields, golf courses, and soccer fields have had
"professional" drainage systems that were major failures.
I became a believer when I saw several friends install "conventional"
French drainage systems which turned out to be such major failures.
It should be noted that the same systems installed on different terrain,
different soil composition and different grades may have turned out
to be excellent systems.
The book is about 200 pages and goes into a lot of the science and
engineering aspects of soil structure, water retention, capillary action,
capillary fringe, perched water tables, subsoil particle movement
(especially through course gravels), etc. While it is a bit technical at
times, it is still presented in a manner that the average layman should
follow easily. It should be fairly easy to do a first reading of the book
in an evening, although you are obviously going to want to go back
and re-read portions at a later time.
You can install a system the "brute force" method and avoid doing
significant research - guessing at intervals between trenches, trench
depth, fill material and so on. The system may work 50% of the time
or more, but is it worth the risk of investing so much time and materials
and winding up with a system which performs very poorly?
FYI: The authors generally suggest course washed river sand as the fill
material rather than gravel. This is discussed in detail.
FYI: Zoning codes are not universal. We can guess about whether your
system must be discharged "to daylight" or can be tied into a storm
(not sewage) system, but a quick phone call to your local zoning folks
will get you the correct answer rather than random guesses from us.
You mentioned sidewalks, which implies that you live in an urban area
with sidewalks and curbs. If you are going to discharge through a curb
cut, then this can present challenges at times depending upon the pitch
of your property toward the curb. Your curb cut is going to be just a few
inches below grade, whereas your drainage system is going to be deeper
than that. If you don't have sufficient grade running down toward the curb,
then you may have a dip in your system which can fill with any fine particles
which enter your system and should normally stay in suspension and flush
from the system.
Some localities will allow a tie-in to a subsurface drainage system, but
never into a sanitary system. A direct tie-in to the storm sewer system
is optimal, but may be not be allowed or may prove to be rather expensive.
Often, a tie-in to the gravel drainage base below your street surface may be
permitted for sump pump discharge, which has relatively clean water, but
not for field drainage systems, which may carry fine particles into the
street's gravel base and diminish its drainage capacity. Even for sump
pump discharge, most municipalities prefer discharge directly into the
curb except for extenuating circumstances such as considerable winter
street ice caused by sump pump discharge into the street.
peter wrote in message ...
What is the correct design for a french drain, should there be a layer of
filter for fine particles, e.g. a layer of weed fabric around the pipes or
outside the pebbles? This drainage system would eventually clog up, right
(all filters clog up eventually). Also, how do you prevent plant roots from
entering and damaging this drainage? Do I have to rebuild the french drain
every few years?
It is alot easier to build this french drain if I can drain the water out
the sidewalk (which eventually drain into the sewage) instead of directing
it into the sewage. Is there a code against this?