swale or french drain for wet basement 3

[jay2000]

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.

 

[dicksewerrat]

Steering the water away from your foundation and around the building is a better idea. you would have to remove the water from the french drain by pumping or having an open end to let the water drain away. French drains normally just let the water percolate into the soil but if you have a way to remove the water it works better. But keeping the water above the surface of the soil and steering it away will work better.

 

[jay2000]

Thanks for the advice. So I take it you consider the swale the best bet. As far as having somewhere for the water to run, I had planned on poking the drain tile out the side of the hill at the edge of my property that borders the public stret. Any advice on what would be the swale dimensions if I decide to go that way? I am worried about the apperance of the swale though. An 18 inch deep swale be quite noticable.

 

[dicksewerrat]

Do you have an idea how deep the water is as it moves over the ground toward your house? If you grade the lawn so it is 10 inches or so higher near the house and slopes away so the 'swale is 30 fet from your bldg. wall and carry ther grade around to the front, it may not be real noticable. What is on either side of you? other homes? You could make your yard a littler higher around the house and slope down till you get to a point that you are below the grade of the nieghbors then bring it back up. This will put the drainage swale away from your house but not impact the others.
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.

 

[jay2000]

Thanks for the advice again. I had entertained the grading option. The only problem with grading is that the soil around my home is already the lowest point in the yard, unfortunately I can't raise that level as the soil is up to the bottom of the basement windows, and if I raised the soil it would block the windows. I could excavate 30 feet of dirt from the rest of the yard but that would be a huge and costly operation. As far as neighbors, my home sits on an acre lot. Both neighbors are a 1/2 acre away. As I stated before I like the swale, I'm just concerned about the apperance.

 

[SirAl]

Proper lot grading about the house is one of the most neglected aspects in residential development. If in fact surface drainage is the problem, surface drainage improvement is the way to go (i.e. forget the french drain).
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.

 

[Focht3]

SirAl has given you a good recommendation regarding piezometers to check for groundwater. But I'd postpone that effort for awhile. Eliminate the surface drainage concern first - then let us know if you are still getting water into your basement. If you are, try to determine when and where the water appears first. Details are important - so be observant.

Don't go the french drain route - this can cause a lot more problems that it solves.

 

[dicksewerrat]

You could put in some window wells and gain a foot around the house. If you have bedrooms in the basement you may have to put in an egress Window for fire protection but the window wells should help.

 

[jay2000]

Thanks for the great advice everyone. All my down spouts extend 3 feet past the foundation. Okay, at this time I want to try and solve this problem with the least invasive method. Since grading isn't a good option, I was leaning towards the swale french drain option. focht3 you stated I shopuld avoid the french drain. Can you explain why?

 

[Focht3]

Sure. A poorly designed and constructed french drain can do a lot of damage. They can introduce water below grade over a broad area, creating a source of water for additional (new) leaks.

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.

 

[jay2000]

Okay the swale sounds good to me as well. My only concern is that I've read the swale should have the same pitch as a french drain 2% per foot, over 70 feet that comes out to 17.5 inches which would be quite noticable. That's why I thought a french drain, being underground would be less intrusive to the eye.

 

[Focht3]

Well, the 2% rule for swales is not as big a deal as it is for french drains. After all, if the slope is only 1%, what happens? The rainwater depth can be greater, and drainage will take longer.

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.

 

[SirAl]

I have found that less than 1% grade for drainage in sodded/landscaped areas including shallow swales is inefficient and depending upon the area of run-off catchment, often not enough to alleviate the water accumulations of a substantial rainfall in a timely manner. While lesser grades may be helpful in reducing the amount of water affecting your house, I wouldn't bank on it eliminating the water problem.

 

[PEinc]

If you build a french (freedom?) drain and it does not work well, it will be expensive to fix the drain. If you build a swale and it does not work as well as planned, it would be relatively cheap to build up or improve the swale's berm. Plus the swale's berm can be landscaped to make it less obvious. I would go with the swale; but this will help control runoff from the hillside only.

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.

 

[VAD]

This is an interesting debate on which I will provide some comments. First it appears that there is no drainage at the foundation level of the basement. Generally weeping tile is used around the footings to take away water that infiltrates the ground and avoid the problem generally of water getting into the basement. It appears that this system is not part of your house construction - assumption based on reading your information.

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.

 

[jay2000]

Okay everyone, once again thanks for all the great advice. At this time I'm prepareing to start the swale. I figured swale first, and if that dosen't help, I'll go with the frech drain. I'll keep everyone posted as to my progress. Thanks agin for the great and comprehensive advice

 

[Grouser]

J2000
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.

 

[Focht3]

That's the first I've heard of a retention requirement for residential property. Where is your practice, [blue]Grouser[/blue]?

 

[cvg]

in this area, 100-year, 2-hour retention is required for all new development. It seems to be getting fairly common in the US in order to comply with NPDES requirements. However, a permit and construction of a basin would not normally be required for a remodel / grading improvements as described here.

 

[Focht3]

That would be a pretty stiff requirement here (San Antonio), although it would certainly help. We have a much bigger problem: Public Works has been collecting "fee in lieu of" for stormwater retention for at least 5 years. Yet not a single retention project has been built with those funds, and the City Manager and Director of Public Works have refused to account for the funds (which were supposed to be kept separate from general funds.) It hasn't hit the media - yet. Given the temperament of the CM and DPW, that's the only way the issue will be addressed...

(Term limits make the elected officials essentially toothless on this issue.)

Sorry for the "off-thread" rant -