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what to do if landscape drains can't be sloped?

Posted by tress21 none (My Page) on
Fri, Aug 5, 11 at 18:02

Two sides of our home have absolutely no drainage, and during a heavy rainstorm the water collects about 4" deep against the house. So we've hired a contractor to install gutters and floor drains in the concrete around the back of our home. They removed the concrete walkway that used to get flooded, and placed PVC drain pipes leading around the house to the driveway.

The problem is, the pipes cannot be sloped with a proper 1-2% incline. There is one area of the pipe that goes through an area with other electrical lines, and the trench cannot be dug any deeper. And GC says he can't raise the other end or the drain will be higher than the floor. So portions of the run are sloped downhill, and others are either flat or even very slightly uphill.

My question is how much of a problem will this be? The contractor ran my hose into the drain and showed me that it exits the drains at my driveway. But when he turns the hose off, there's a significant residual--probably several gallons of water that are left in the pipes. Will this cause problems with mosquitos, mold, etc?

Follow-Up Postings:

RE: what to do if landscape drains can't be sloped?

Obviously this is too vague to offer a definitive answer but if the collection pipes are linked to a pit so that the water does run downhill into it and then a sump pump empties the pit to daylight problem solved.

RE: what to do if landscape drains can't be sloped?

My daycare lady has a sump pump that they use for draining an area near there garage that pools water -otherwise you won't get water to flow uphill.

RE: what to do if landscape drains can't be sloped?

Thanks inkognito and isabella. Just read up on sump pumps, as this is my first house and I'd never even seen a sump pump before.

The area where I am placing the drains is a long, narrow walkway between the house and a retaining wall. Our GC says there would be no space to dig the sump pit and put the pump. Apparently, there's also several enormous municipal drain lines that run across the area, preventing any trench from going deep.

The best option we could see would be shortening the drain line and leaving half the area without drains. I'm guessing that most of the rain is coming off the roof, so when the gutters are installed I could still bring most of the water over to the shortened drain line. That would mean having to do some very creative (and awful looking) gutter downspouting--one downspout would have to travel about 4 yards horizontally, above a door, as it came down. I suppose that's less awful than having drain pipes that run uphill and flooding my foundation. Still, I hate to be responsible for ugly construction!

RE: what to do if landscape drains can't be sloped?

Downpipes can be very elegant! They can be designed with nice curves, slopes, and junctions. Think of them as a feature, maybe use copper or something showy, or paint them the trim colour, and you won't resent them. It seems more logical to do the gutters before the drainage, but if you are at the drainage already, you could do what can be done, and then work on reducing water inflow.

Are your drain pipes going to be perforated? If so, then the residual should gradually seep out.


RE: what to do if landscape drains can't be sloped?

I assume that, besides adding gutters and downspouts, your contractor has also addressed any negative grading issues along those two foundation walls. If that has been done and you still can't get an adequate slope with the current drain leading to the street, what about inkognito's suggestion of digging a downhill pit elsewhere (?maybe in the back yard) and leading the water there instead of the street? This would be a more environmentally friendly alternative to contributing more surface runoff onto the streets. The pit could be designed to act as a cistern in times of drought, covered with vegetation to create a rain garden or simply backfilled with gravel. In the long run, whatever you do to correct the issue now will be much less expensive than dealing with a cracked foundation later...

RE: what to do if landscape drains can't be sloped?

The problem here is generally one of a very flat lot with surface water at an elevation not sufficiently high enough to be easily routed to a lower discharge point.

Since the problem is one of the water existing too low in the landscape already, it is probably a bad idea to allow the water to go from it's elevation on the surface to a lower level in a pipe.

The correct method for resolving this type drainage problem is to start by developing an accurate site map with elevations. At this time, it is premature to consider a drainage pipe of any kind.

RE: what to do if landscape drains can't be sloped?

Ideally, from what's been said, directing the ground water and the gutter runoff to a pit with a sump pump would be the best answer. Such a pit doesn't need a huge area.

From your post it sounds as though the majority of the work has been done since the GC has done a test with the garden hose. Personally, if I had to work with what was already installed, I'd choose a few gallons of water left in the drain pipe before I'd leave half the area without drainage.

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