swale or french drain for wet basement
swale or french drain for wet basement
(OP)
Hi, I’m receiving water in my basement after a heavy rain. My property borders up to a
large hill. I’ve read several places that a swale or outside French drain could help my
problem. Here are my questions?
1. Which is best swale or outside French drain?
2. I’ve read that a swale should be approximately 10 inches wide and 2 inches deep
with a 1/8 to 1/4 inch drop per linear foot. The length of area I would need to
cover is approximately 70 feet which would mean the drop would be 8.75 for the
1/8 value and 17,5 for the 1/4 inch drop, which I believe would be quite
noticeable in the yard.
3. If I decide to construct a French drain I’ve read that there is a 1 inch bed of
gravel, 4 inch drain tile and another 1 inch bed of gravel followed by a 1 inch
layer of top soil. I’m not sure if I would need some type of surface drains tied
in to the drain tile, or does the water naturally soak through the ground into the
drain tile. I’m also assuming that the ditch depth should be approx. 76 inches
deep. 1 inch for gravel, 4 inches for drain tile, 1 inch for gravel and one nch for
top soil with the same pitch as above 1/8 or 1/4 per foot.
So there’s the situation. Water in basement, swale or french drain,which is best.
Thanks ahead for any advice regarding this isssue.
large hill. I’ve read several places that a swale or outside French drain could help my
problem. Here are my questions?
1. Which is best swale or outside French drain?
2. I’ve read that a swale should be approximately 10 inches wide and 2 inches deep
with a 1/8 to 1/4 inch drop per linear foot. The length of area I would need to
cover is approximately 70 feet which would mean the drop would be 8.75 for the
1/8 value and 17,5 for the 1/4 inch drop, which I believe would be quite
noticeable in the yard.
3. If I decide to construct a French drain I’ve read that there is a 1 inch bed of
gravel, 4 inch drain tile and another 1 inch bed of gravel followed by a 1 inch
layer of top soil. I’m not sure if I would need some type of surface drains tied
in to the drain tile, or does the water naturally soak through the ground into the
drain tile. I’m also assuming that the ditch depth should be approx. 76 inches
deep. 1 inch for gravel, 4 inches for drain tile, 1 inch for gravel and one nch for
top soil with the same pitch as above 1/8 or 1/4 per foot.
So there’s the situation. Water in basement, swale or french drain,which is best.
Thanks ahead for any advice regarding this isssue.





RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
Put some lathe stakes in around your house where you think the lowest part of the drainage swale will be. Then adjust to make it as unobtrusive as you can before you do any excavtion and reshaping.
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
Maintaining a positive grade dipping away from the house, on all sides, is important. General lot grading can then be designed to direct surface runoff as required without intrusive swales. It is important that near-by neighboring properties are not affected by your drainage modifications. If in doubt, consult a municipal engineer experienced with land development.
Also, if your roof leaders discharge onto the lot surface, ensure that you have downspout extensions or other methods in place to direct the roof water well away from the house foundation. Same goes for sump discharge if applicable.
As a final comment, although it does sound like a surface drainage issue, ensure that the problem is not interflow or groundwater related by installing a couple of piezometers (i.e. 1" diameter plastic/pvc pipe with the bottom 5' slotted with a hacksaw). I would insert this into a 6" diameter (or as small as you could make it) hole, to a depth of about 10', one at the front and one at the rear of your house (ensuring that you are outside the original basement excavation). The pipe could then be backfilled with sand and sealed at the surface (top 3') with tamped clay. Measure down periodically with a tape measure to see if water is present in the pipe. This will be an indicator that you have a groundwater issue. Subsurface drains would be required if this is the case.
RE: swale or french drain for wet basement
Don't go the french drain route - this can cause a lot more problems that it solves.
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
For a properly constructed french drain, you would need a good slope (about 2%) to the trench bottom, and appropriate backfill for the soils at your site. If you put a collector pipe in it, it will need a proper filter fabric around it to keep it from clogging. This is a very cursory description of the design/construction issues - and we haven't talked about maintenance!
Swales are easy to build and maintain. And they are unlikely to cause additional damage to your structure.
In general, you should try swales first. If they don't work, then you may have to use french drains.
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
The intent of the swale is to divert the water away from the building. If you can accomplish that with a grade of less than 0.5% - great! But the flatter the slope, the more time you are likely to spend maintaining the drainage pattern.
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
Even without runoff from the big hill, you may have a problem with the ground surface adjacent to the house being the low point in the yard. Downspout discharge will not drain away from the house. It can seep down the foundation wall causing hydrostatic wall pressure, wall cracking, and leaks. In periods of extended cold weather, this moisture in the ground can freeze and exert great pressure on the foundation walls (especially along the north side of the house). In winter, when there is snow on the ground and the snow starts to melt off the roof, the snow on the ground will prevent the downspout discharge from draining away from the house. This leads to more seepage and leaks or to more freezing pressure. It is important to regrade the lawn area away from the house and/or to carry your downspout discharge much farther than 3' away from the house so that it doesn't come back to the house.
RE: swale or french drain for wet basement
The debate regarding the swale or french drain is interesting. Nothing is terribly wrong with the french drain. However it appears that everyone is basing their comments on surface water runoff that eventually percolates in the ground. Is this the only source of the water or is there ground water flow as well. SirAl has provided valuable comments.
Something is not correct or strange if this water appears in your basement and you cannot trace it as water perhaps entering from the surface.
I will provide some personal experience I had after a heavy rainfall beating against my house. The next thing I saw one day was water in a part of my basement. On examining outside the house I found that there was a possibility of rainfall water seeping down through the join of a walkway slab and the basement wall. As a temporary measure I applied some caulking at the location and also added a piece of siding (aluminiun) and used it to direct the rainfall from falling directly and accumulationg at the join area. I perceived that there was a low spot at the location and all was needed to deflect the water away from there. Since then depite heavy rains I did not get a recurrence of the problem.
I had intended to do some additional work but since the situation did not occur again I left it alone. I did not like the siding propped up by some boulders as my rain deflector arrangement but at the location it is not visible
and hence I really do not have to see it.
There are ways to construct french drains that would prevent water they transport from seeping into the ground. I presume that you would want the surface exposed to colect the water and move it downwards. That is why everyone likes the swale approach. For the French drain you can use an impermeable liner sandwiched between geotextile. If water is expected to seep underground the side facing the hill will nhave no liner but geotextile only. This system of liner geotextiel combination can be produced quite easily through your friendly geosynthetics supplier.
Hope this helps with your conviction of the french drain for aesthetic purposes, however you need to understand what the two systems do and which suits your problem best.
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
Be sure to check with your local governmental unit to find out how much storm water must be retained on your property before 'designing' your drainage system. Many jurisdictions use the first inch of rainfall. This means that one twelfth foot times your 43,560 SF acre lot equals 3,630 cubic feet of water to be stored on site!
Condider grading the 'lower' ends of the swale into 'ponds' to retain this water or fill the graded depressions with gravel and cap with backfill if appearance is important. Make sure the storage well can drain away from the house when full. The piezometer idea will help with locating the water storage(not upstream of the house).
Good luck.
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
(Term limits make the elected officials essentially toothless on this issue.)
Sorry for the "off-thread" rant -
RE: swale or french drain for wet basement
I checked with a colleague and verified the minimum 'treatment' requirement for all sites in Miami-Dade County is the first inch of rainfall. This volume cannot join any surface runoff leaving the site.
It is my understanding that project sites where less than 5 acres of soil will be disturbed are not covered by NPDES and a Storm Water Pollution Prevention Plan (SWPPP) is not required.
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
Please see FAQ731-376 by VPL for tips on how to make the best use of Eng-Tips Fora.
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
Please see FAQ731-376 by VPL for tips on how to make the best use of Eng-Tips Fora.
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
Please see FAQ731-376 by VPL for tips on how to make the best use of Eng-Tips Fora.
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement
Please see FAQ731-376 by VPL for tips on how to make the best use of Eng-Tips Fora.
RE: swale or french drain for wet basement
I recently installed a french drain at the base of the hill, approximately 20 feet from my foundation (3ft deep, 4" perforated pvc pipe wrapped with fabric sleeve, surrounded with 3/4" clean stone). The drain is working great--water has been flowing out of the outlet pipe constantly since i put it in.
One problem--my sump pump is still running just as much as it ever did. I'm talking about a lot of water--the pump is 3/4hp, 1.5" outlet pipe, runs for about 40-50 minutes every 3 hours.
My question--should I have dug my drain deeper? Do i need to take the base of the drain down to the basement floor foundation level to keep the sump pump from running so much? Should I build a new, deeper french drain parallel (closer to my house) to the first drain I dug?
Also, should I wait for the ground to dry up before I excavate again?
Also, apparently my footing drains are blocked. Is their any way to clean out the footing drains without draining my bank account?
RE: swale or french drain for wet basement
I have a similar issue with my house--sits at the base of a large hill and my back yard is very wet. My sump pump runs frequently. ...One problem--my sump pump is still running just as much as it ever did. I'm talking about a lot of water--the pump is 3/4hp, 1.5" outlet pipe, runs for about 40-50 minutes every 3 hours.
That isn't good.
I recently installed a french drain at the base of the hill, approximately 20 feet from my foundation (3ft deep, 4" perforated pvc pipe wrapped with fabric sleeve, surrounded with 3/4" clean stone). The drain is working great--water has been flowing out of the outlet pipe constantly since i put it in. ... Also, apparently my footing drains are blocked. Is their any way to clean out the footing drains without draining my bank account?
I'm glad your new french drain is working, but you should know that the stones will clog over time as the clays work their way into the voids between the stones. That's what probably happened to your footing drains. And there's no way to clean the drains - you'll have to dig them up and replace the stone. This time you should put a filter fabric between the stone and soil, too. Or use concrete sand instead of washed stone.
My question--should I have dug my drain deeper? Do i need to take the base of the drain down to the basement floor foundation level to keep the sump pump from running so much? Should I build a new, deeper french drain parallel (closer to my house) to the first drain I dug?
Are you getting water into your basement? You should hire a local geotechnical consultant to see whether a new, deeper french drain is needed. This is a problem that really needs to be seen -
Also, should I wait for the ground to dry up before I excavate again?
I would!
Please see FAQ731-376 by VPL for tips on how to make the best use of Eng-Tips Fora.
RE: swale or french drain for wet basement
RE: swale or french drain for wet basement