Prevent Flooding on Sloped Yard with Culverts and Curtain Drains

LESLIE: Rob in Washington is on the line and is dealing with some flooding. Tell us what’s going on.

ROB: Well, I own a 1-acre lot and I’m surrounded by 58 acres of green belt. And my house sits up in the front of the lot and I have a cement driveway that runs down into a 1200-square-foot shop. And every time it rains it here in Seattle, which is every other day …

TOM: Yeah, frequently.

ROB: And at Daylight Saving, we get an extra hour of rain. But I get – my shop floods and I need to know what kind of drain system I can put in in front of my shop. The cement is maybe 14, 16 feet wide.

TOM: So basically, Rob, what is happening is the water is running down the cement driveway and into the shop. Is that the main source of the water? What you need to do is to put a culvert across the driveway.

So the way that works is you, essentially, cut the driveway in half; you slice out a gap in the driveway. And it might be 8 or 12 inches wide.

ROB: How close to the shop though?

TOM: I would go probably a few feet in front of it. I wouldn’t go too far away.

ROB: OK.

TOM: Because that just gives you more water – more sidewalk to collect sort of in front of it. So I would go fairly close to it. And then you basically cut the driveway in half and you drop this culvert in, which is sort of like a U-shaped channel. And then on the opposite end of it, it’s attached to a drain line, which would go to a curtain drain.

So the water would go down the garage, it would fall into this culvert. And you can buy these or order these at building-material supply centers that service masons. And people that do more commercial-type work can be able to find these premade. And the drain tile – the drainpipe – will connect to the culvert so the water would go out to this drain line and then you go into a curtain drain.

So the curtain drain, also known as a French drain, you’d make yourself. And again, on the downside of the property, you’d curve out an area about 12-18 inches wide and deep, fill it with stone, lay the drainpipe in there, cover it with more stone, put some filter cloth and then some topsoil or whatever you’re going to cover it with.

So, essentially, the drainage for this is invisible once it’s done but you’re intercepting that runoff down the driveway and running it around the building and into the drain tile. And that pipe that you install there must be perforated. And I would recommend using solid-PVC perforated pipe, not the flexible, black, landscaping perforated pipe.

ROB: OK. Thank you, guys.

TOM: Good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.