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seabright_sc 01-05-2008 01:54 PM

The Bioswale, french drain, deck, drainage dilemma (long)
 
Hello there, I'm new here and looking for a little guidance. Here's the deal....

My wife and I bought a new construction home in May07, 6000 sqft lot, house and garage has about 1500 sqft footprint.

Back yard was not landscaped... just a big space will fill dirt. Our county is trying to reclaim groundwater so instead of installing drains... new home are required to have lots graded with "bio swales"Ö just a fancy way of saying... the lot is graded so that the water travels a path about 12-18 inches wide... along the back of the house (about 3 feet away), out the side yard (where you'd expect a paved walk way instead of dirt walkway/stream bed), and to drain box that pipes to the gutter.

Well here's our problem. Summer came and my wife and I were anxious to use our back yard. So a friend suggested:

Putting in a french drain under the bio swale and leaving the grade as intented. Then building a low deck (about 12 inches in height) about 600 sq feet) free standing against the back of the house with the french drain and bioswale running the length of the deck then the back of the garage (and eventually out both side yards to the drain boxes).

We went for it. Drain was installed w/ 4 inch pvc with two rows of holes along the bottom of the pipe, gravel in base of trench, pipe wrapped in landscape fabric, a little more gravel, and then few inches of soil (clay) on top. Down spouts were extended about 3 feet to meet up with the bio swale but not directly tied into to French drain


Drain (as with the swale) is sloped, slightly, to the outlet by curb. Deck was built.

First real storm came (about 3.5 inches in 24 hours). Here's what I noticed. Water, more so than we expected, was flowing about 2-3 inches deep in the swale (above the drain), under the deck around the house, to the drain box. No way to tell how much, if any, water was percolating into the drain. I suspect not much since the soil consists of clay.

I pulled up a couple of deck boards next to the house and noticed that water was against the slab foundation. About an inch deep, but no matter how heavy the downpour (and this was a BIG storm for us), the water was not rising and WAS indeed moving out under the deck, in the swale, etc.

12 hours after the rain (about a 20 hour downpour!), water was NOT standing next to foundation and had flowed out along the swale.

Sucks... but I think that I'm going to remove about three feet in width of deck boards (about 40 feet - the entire lengths worth) along the back of the house and build up a bank of soil so that the water stays in the swale and not along the foundation. I have about 6 inches foundation between the ground and the siding). Obviously the guys who did the work did not pay attention to the grade close enough!! (but the deck came out nice).


Question # 1 Can this wait till the spring... This storm was the heaviest in years and the water along the foundation never raised more than a couple of inches and subsided completely within hours of the rain stopping). Or should I bite the bullet and start pulling up deck boards and building up soil as soon as the rain stops?

Question 2: As mentioned the swale exits from under the deck, runs along the back of the attached 2 car garage, and around the corner along the side of the house out to the drain box.

My wife and I would like to put in some kind of walkway along the side of the house and a little patio of sorts (or just continue the walkway) along the back of the garage to meet up with the deck. Problem is.... that's where the swale is (Think water path) and just a few inches below you start hitting the gravel and cloth of the french drain.

Ugh! I'm beginning to think the french drain may not have been needed! I donít even know if water is even entering the drain (I have since been told that French drains work great for rising water table which supposedly is NOT a problem in our area) If be build a patio, concrete path, flagstone path, etc, it can't be built up, or it'll obstruct the flow of water. Canít much lower we can go because the french drain. So we're looking for ideas of what to do besides just having a dirt bioswale, drainage zone-water path, in a prime walkway and patio area. Not even sure if we can plant grasses since there is so little soil above the drain. One thought was just to remove about half the French drain so that we can put in the patio and/or walk way and have the grade continue itís current path. Ugh.


Any advice? Thoughts? Next time I'm getting more than one opinion!


timber 01-05-2008 03:19 PM

Sounds like your drain is functioning fine, but having a soil buffer between the swail and the foundation would be good. During a large rain storm especially in clay soils ( we have clay where I'm from) the water runs fast and quick, so the tile is soaking water, just not quickly until the soil is saturated. After the rain stops, the perf. tile is in place so there isn't any standing water issues. Do you have a basement? I'm not sure I'd get to worked up about it if the water dissipates. Some pics would be really helpful.

seabright_sc 01-05-2008 03:37 PM

Thanks for the reply. No basement. I've heard conflicting comments. Some say if the water dissipates shortly after rain, don't worry too much if there's a little water against the slab. Others have said dont let any water against the slab. We get an average of 30 inches of rain. Majority between Dec. 1-may 1. So it's early in the season. Hopefully I'll round up a digital camera to show pics.


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