[FrenchDane]

Hi all. New to this forum, thanks in advance for any advice you can spare.

My home is on a rectangular city lot that has a negative grade from the street (about 6" lower at the back lot line). I'm blocked in on all sides by neighbors.

I get a lot of standing water in the backyard corner during and after storms and need a solution to drain that to the street. It's a 125-ft run from the back of the lot to the street. I don't know anything about drainage, and here's the options I'm considering:

Option A:Level the yard, then add a "sunken" french drain, discharging the water with an emitter

If I bring the yard to level, I've only got 6" of drop to use over 125 feet. (6" is the height of the curb at the street.) Not enough room for slope and not deep enough to bury pipe/gravel.

Instead, I'm thinking I can add a "sunken" system that terminates lower than the curb elevation, then use a 90-degree pop-up emitter to discharge the water.

I'd install about 20' of traditional perf pipe french drain in the backyard which would then connect to a solid run of pipe (~95ft) ending at the emitter. Trench floor would start at -9" underground and terminate –18" under the curb elevation. This yields a 1% slope, but the kicker is, water would need to travel vertically ~24" to exit through the emitter. Yep, the discharge is higher than the intake.

I never took a physics class so I have no idea if enough pressure can build at the back end of this system to force water out of the emitter?

This would be my preferred option since just leveling the yard would leave my house untouched.


Option B: Bring yard to level, then add a ~30ft stretch of 1% lot grade in backyard
In this option, the french drain would collect water at the base of the new grade, perpendicular to the lot, with a 1% slope. It then connects (L-shape) to a solid PVC pipe running lot-parallel for a mostly flat 95ft stretch, exiting through a curb cut. My concern here is whether there's enough pressure to push water through that long stretch of flat pipe.


Option C: Regrade the entire yard, front to back, incorporating a .25% slope.
I'm trying to add as little material as possible to my yard, in order to not bury my house in the process. This option doubles the height of the grade to 12" at the highest point in the backyard and gradually slopes down to 6" where it meets the curb, again a 125' run. Assuming a 4" diameter pipe, this give me about 5in of cover for the french drain in the back, which again would connect to a parallel solid pipe (L-shape) daylighting at the curb cut at 0" grade. Concern here is the very low % of slope.

Are any of these ideas viable, or is my approach completely wrong? Note that sump pumps are not an option.

Thanks a million in advance. Added an image with some diagrams if that helps.

 

[Nealtw]

Option A won't work.



Just to change your thinking a little.
a 4" pipe that is level has a 4" drop from one end to the other

Water will always find the low point exit

So the french drain in the back yard can be level it will take all the water you can give it, just not as fast as you might like in a downpour. Then you can work to the curb with a minimal slope.

 

[3onthetree]

A picture of the house/yard would be better for advice. Is it a soil gangway (3'-5' wide)? Is it similar on both sides of the house? How much of the water is from your downspouts? From your neighbors? How high is your concrete foundation (can you raise grade to curb level or do you have a step down on the house)? With a curb, is there a sidewalk you have to traverse a pipe under? Can you really make a curb cut (never see this allowed anymore)? Can you really dump your water to the street (ditto)? Is there a front yard?

 

[Bondo]

I've only got 6" of drop to use over 125 feet. (6" is the height of the curb at the street.)

Ayuh,...... How did you come up with yer grade numbers,..??

Was a laser transit used,..??

 

[FrenchDane]

Option A won't work.



Just to change your thinking a little.
a 4" pipe that is level has a 4" drop from one end to the other

Water will always find the low point exit

So the french drain in the back yard can be level it will take all the water you can give it, just not as fast as you might like in a downpour. Then you can work to the curb with a minimal slope.

Thanks Neal, slapped the table when I read your note. How can I get the most out of that 4" of drop inside the pipe? Do you think I can get away with a relatively level and shallow drain, over a long run?

I'm thinking something like 8" deep and as wide as needed. I could drop two pipes in it really.

 

[Nealtw]

Thanks Neal, slapped the table when I read your note. How can I get the most out of that 4" of drop inside the pipe? Do you think I can get away with a relatively level and shallow drain, over a long run?

I'm thinking something like 8" deep and as wide as needed. I could drop two pipes in it really.

I didn't do the math but I would start at the level you can get thru the curb and the bottom of the french drain pipe can be just an inch or two above that and then what does it take to hide the pipe.

 

[FrenchDane]

A picture of the house/yard would be better for advice.

Thanks 3. Attaching a drawing here. I'm in central Texas. The lot is ~6000sqft, with front yard, backyard and ~8ft wide sideyards. Soil is "Houston Black Clay" which is relatively good at draining, but retains a lot of water and stays soft a long time.

The lot is 70 years old and hasn't been improved since. There's currently nothing in terms of drainage or landscaping and I'm in the early stages of planning an overhaul. Adding a driveway, sidewalk and general landscaping.


The house is pier and beam with a 3ft crawlspace. So technically I could build up around it, but I'm trying to avoid it.

My roof is metal and currently don't have gutters. It's also gabled in a crazy way with a lot of valleys. Water is rushing fast off the roof. Part of the plan is to add 5 downspouts draining into a separate trench/pipe system to the street.

Besides that, the neighbors behind and to the south share the "low point" in the yard that collects standing water. Whatever solution I go with will affect their yards. I've checked with the city and as long as I don't direct water into their yards, I'm free to regrade as I please. If I instead keep the grade flat and have some kind of trench, I will more than likely be improving their situation.

As far as I know, curb cuts/boring curbs are city approved in my area.

 

[FrenchDane]

Ayuh,...... How did you come up with yer grade numbers,..??

Was a laser transit used,..??

Thanks Bondo. No lasers at all. Just eyeballing. I definitely know the yard is sloping negatively away from the top of the street curb (which is 6" tall).

I'll measure with a line this weekend, but when standing at the back lot, I'd say I'm a good 6-12" lower than the front.

 

[3onthetree]

So your new driveway will have to be built up too? One thing about dumping that pipe at the driveway apron, if the back is also a french drain, for a few days after the rain stops you may have to drive through a puddle at the curb.

As far as all the pipes, I don't know, because taking roof water you need good slope or you'll have backup over that length of pipe. I would probably try to dump both sides into one daylight on the street opposite the driveway (but only with good slope of pipe). But my preference is always to regrade first, then swales or small retention areas away from usable yard areas, and if you still can't accomplish drainage, then think underground, but keep it simple. If you have a greenlight on raising grade, and it doesn't affect the house, I'd tip the scale to that since you don't want the grade sloping towards the house anyway.

P.S. I think you need 6 downspouts and maybe some massaging in that dead valley.